Point Access Blocks and Fire Life Safety

May 28

Introduction: Point Access Block Design and Single-Stair Apartment Building Code Reform

Perception: Point Access Blocks and the Perception of Safety Risks

I continue to think about the differences in the perception of safety versus the changing reality of safety. Perception is often based on time-tested measures, but with technology changing and human demographics changing so fast, time-tested is becoming an obsolete understanding.

The building and fire codes started out as insurance-based requirements, to help prevent disasters that insurance companies covered, like buildings. These initially were prompted by multi-building fires in cities. As the codes developed, they continued to evolve as reactions to further fire disasters. Shirt Waist factory, Winecoff Hotel, Copacabana and Station nightclubs, MGM Grand, and World Trade Center fires have all had impacts on the codes.

Other disasters, like Twin Parks North West, have not. Mainly because there will always be human behavior to circumvent the protections the codes can provide. But we try, placing more burden firefighters and rescue operations.

I do not want to place any more burden on them, so the perception that two stairs in larger buildings are safer than one stair in a small building needs to be broken. Our brain’s natural hesitation on any situation that involves feeling trapped needs to be rationally overcome. Reliability of protection systems and sheer probability make PABs safer, being 10x less likely to have a fire in the first place because there are 10x fewer apartments in the building.

Time-tested perceptions based on building disasters that have little in common with modern building protection measures need to be reimagined, now.

Additional protection measures that I would recommend to include to extend the allowances of International Building Code (IBC) Section 1006.3.4(1) from 4 to 6 stories would be an enlarged floor landing, 76” minimum, on the stair to accommodate those who cannot physically go down the stair, escape windows in street-facing stair, if the stair is provided with a street-facing side, supervised sprinkler system per 2024 IBC 903.4.1, 903.4.2, and National Fire Protection Association (NFPA) 72.

These measures address those that cannot physically get down the stair, those that wait to egress with firefighters present in the stair, and continued reliability of the sprinkler system. These additional items address the primary concerns that building geometry does not.

Core Argument: Point Access Blocks and Fire Safety Code Requirements for Multi-Family Housing

Small single-egress-stair apartment buildings, known as Point Access Blocks (PABs), have housed people in cities around the world for many decades. Paris, Berlin, and London have relied on this building type for the primary dwelling stock of their cities, and their codes reflect that history. The difference between those countries and the United States comes down to height. European codes permit PABs at six stories and above, often with elevators. U.S. codes currently cap them at four stories, largely on stated concerns for the life safety of occupants and firefighters. The concern centers around the single-point failure potential of access to a second means of egress.

This book examines those concerns directly and tests them against the data. It shows how modern protection systems, sprinklers, protect occupants, speed egress, and protect firefighters while they work. It analyzes historic fire tragedies alongside modern construction techniques to address the core objections: the risk of a single point of failure, firefighter access conflicting with occupant egress, and firefighters becoming trapped by fire they didn't see occurring. Building fire science, egress modeling, and NFPA incident data drive an item-by-item comparison with code-permitted two-stair buildings, and that comparison shows two-stair buildings carrying more risk, not less.

Finally, this book lays out the code pathways already available in the U.S. and Canada, and how to bring this case to city officials, building departments, and fire officials, so more communities can permit PABs. The goal is straightforward: more housing options for more people, without asking anyone to accept less safety for the families and communities we build for.

This book covers multi-family apartment buildings specifically, not other building types or occupancies. Apartment buildings have unique conditions that make PABs safer than large two-stair apartment buildings, and the chapters that follow explain exactly what those conditions are and why they matter.

Who This Book Is For: Architects, Developers, Building Officials, Fire Officials, and City Policymakers

Architects designing PABs and guiding clients through the approval process will find the technical guidance they need here. Developers evaluating the benefits and pitfalls of building a PAB will find a clear-eyed accounting of both. City officials, building department reviewers, legislators, and fire department officials will find the data and framework they need to evaluate these buildings on their merits. And anyone curious about how small single-egress-stair apartment buildings actually perform on life safety will find a straight answer, backed by evidence.

What Readers Will Take Away: A Code Compliance and Housing Policy Reform Reference

Readers will leave this book with a working understanding of building and fire science, a clear picture of what modern protection systems actually deliver, and a corrected view of a common but mistaken belief: that small single-egress-stair apartment buildings are less safe than large two-stair buildings. Readers will also leave with the data and arguments needed to make that case to state and local officials, along with examples of communities that have already approved this building type.

Executive Summary: Single-Stair Apartment Building Safety and Missing Middle Housing Policy

The question is: are small single-egress-stair apartment buildings, known as Point Access Blocks (PABs), equivalent in life safety to large two-stair apartment buildings?

The data shows they may exceed equivalency. PABs reduce both the probability that a fire ever threatens someone outside its unit of origin and the time that person spends exposed to smoke, if it does. Sprinklers and compartmentation cut the odds of a fire escaping its unit to a low single-digit percentage. This quality apply to both single and two stair buildings. 20 feet of travel distance in a corridor, against likely over 100 feet in large buildings, cuts the time a person spends exposed to whatever smoke does escape a unit fire. Multiply a lower probability by a shorter exposure window, and the result seems clear. A building type that provides both lower probability and lower exposure if it does.

That advantage applies to firefighters as well. The same short travel distance that gets a resident to safety faster also provides a crew less exposure and less distance separating them from their own way out. Firefighters face the same tenability clock occupants do; a building that shrinks that clock protects both.

Two scenarios are the exception:

1) a fire that starts inside the stairway enclosure itself. Here, a second stair provides a genuine advantage a single stair cannot fully replicate. The 2027 International Building Code (IBC) will minimize this risk in PABs by prohibiting outlets, but that won't eliminate it. That is one case where this book's equivalence claim doesn't stretch to superiority, and it's the reason for building exterior rescue balconies rather than relying on stair count alone.

2) an apartment door fails to close, allowing free flow of smoke and fire to enter the corridor. Here, as well, the second stair provides an advantage if the fire escapes the apartment, but if it is just smoke, the long corridors to the stairs will be a distinct disadvantage.

Everywhere else, the built-in geometric protection PABs offer, shorter distances, fewer occupants per exit, faster clearance, outperforms the long hallways and larger occupant loads that come standard with large two-stair buildings. PABs meet the equivalent-protection standard the code has always been chasing, and in most of the scenarios that matter, they exceed it. Cities need to allow them, not as an exception to the safety standard, but because the evidence shows they meet it, and because doing so opens more lots, more investors, and more housing to more people who need it.

Point Access Blocks: Correcting an Outdated Fire Safety Assumption

Lower Probability and Shorter Exposure

Small single-stair apartment buildings, also known as Point Access Blocks (PABs) are fundamentally safer than large two-stair apartment buildings. Bigger doesn't mean safer. The fear of being trapped by a single stair made real sense a century ago, when buildings did not have reliable active protection systems. Modern fire protection, modern construction materials, and active code enforcement have changed that equation, and the data backs it up.

You've heard the disaster scenarios. Grenfell Tower and Dykeman Street both became multi-fatality disasters in single-stair buildings, and both get cited as reasons to distrust the building type. What rarely gets discussed is why those fires turned fatal, and the reasons matter more than the stair count. It is also likely that you have not heard that modern single-egress-stair buildings have operated in New York City and Seattle for decades, because there's nothing to report. No comparable incidents have occurred there.

What Historic Apartment Fire Disasters Actually Show in PABs

Every apartment building fire disaster in the U.S. over the last decade has occurred in an older building. Dykeman Street, built in 1910, and Twin Parks Northwest, built in 1972, both fit that pattern, and both were largely preventable with proper maintenance. These fires share a common thread: aging construction, missing or disabled protection systems, and maintenance failures compounding into worst-case outcomes, not a fundamental flaw in single-stair design. Neither building had an automatic sprinkler system.

Dykeman Street was an open stair apartment building built in 1910 and the fire was started by a man flicking a cigarette butt onto cardboard boxes left in the corridor. The 6-story stair became a chimney which quickly spread fire and smoke to all floors. People escaped down the fire escape, through their windows.

Grenfell Tower and Twin Parks North West disasters came down to apartment doors not being closed, allowing smoke to easily fill corridors and stairs. Either by the failure of door closers (Grenfell) or the doors being propped open (Twin Parks), these breaches of the compartmentalization protection affect primarily the corridors people travel to the stairs. Longer corridors means longer exposure to smoke. In both of these fires, the fire did not escape an apartment, blocking access to any way out, it was all the smoke that caused to disaster.

Why Fire Containment Fails: Case Studies in Apartment Building Fire Safety Design

Apartment buildings have a structural advantage most building types don't, shared mainly with hospitals: compartmentalization. Each apartment sits inside a box formed by one-hour-rated walls and one-hour-rated floors and ceilings, built specifically to stop fire and smoke from reaching neighboring units where people may be asleep. Add a rated corridor wall and an active sprinkler system, and a fire that starts in one apartment is very likely to stay there. National Fire Protection Association (NFPA) data backs that up directly.

So why doesn't this work every time? The primary reasons fires spread beyond the unit of origin come down to two things: lack of maintenance and human behavior that defeats the fire-rated walls the code relies on. Lack of maintenance usually means a fire-rated door no longer closes and latches on its own. Human behavior usually means someone propped an apartment door open or put a hole in a wall. Either one sidesteps the entire compartmentalization strategy the code was built around.

Doors are exactly where Grenfell Tower and Twin Parks North West turned from a contained fire into a disaster. Dykeman Street was caused by the single stair being open to all corridors and apartment doors, something current code does not allow. Which is why I feel that allowing apartment doors opening directly into the stair an unsafe idea.

Dykeman Street was a six-story apartment building with a fire escape and a central stair that ran open to every hallway and every apartment door on every floor. When someone flicked a cigarette into a pile of cardboard boxes, that open, six-story stair acted like a chimney, and the fire grew and spread fast. One tenant reported opening their apartment door to leave and finding fire already there; they escaped down the fire escape instead. Most apartment fires start inside units, which is exactly why apartment doors should open into a corridor that leads to a stair door, rather than opening directly into the stair itself, even where code still allows it.

Grenfell Tower and Twin Parks North West are both high-rise apartment buildings, and both illustrate a different failure mode. At Grenfell, fire on the building's exterior broke windows and entered individual units. When apartment doors failed to close behind residents fleeing those units, smoke spread rapidly into the corridor. The fire itself didn't spread through the building; the smoke did, moving through open doors into the stair. Malfunctioning door closers caused the tragedy, not a structural failure of the compartmentalization concept.

Twin Parks North West had two stairs, and the fire never grew beyond its unit of origin, because firefighters arrived and extinguished it quickly. But the unit door had been propped open for air circulation, and so were the stair doors on multiple floors. Smoke filled the third-floor corridor, climbed the open stairs, and filled corridors many floors above the fire. That's where most of the harm happened, because propped-open doors defeated the very system meant to stop it.

Containment in modern apartment buildings focuses on two systems, fire-rated walls and floor, and sprinklers.

Opposition Point: IAFF Concern, Single Point of Failure

The International Association of Fire Fighters (IAFF)'s position statement puts it plainly: a single-stairwell building provides only one path of egress, and if that route is blocked by fire, smoke, explosion, or structural failure, occupants and fire fighters face catastrophic consequences. The statement grounds this in the Triangle Shirtwaist Factory fire of 1911, where locked exit doors and a single collapsing fire escape trapped 146 garment workers.

A blocked or compromised sole stairway is the worst-case outcome any egress system is designed to prevent. The instinct to demand a second way out has history.

But is that history still relevant in modern apartment buildings?

Three things distinguish a modern Point Access Block from Triangle Shirtwaist or Dykeman Street:

- Automatic sprinkler systems and fire alarms with smoke detection,

- The stairway is a rated, enclosed, sprinklered enclosure rather than an open shaft, and

- Every apartment door swings into a corridor rather than opening directly into the stair.

The Minnesota DLI/WJE-Crux event-tree modeling discussed previously treats a stairway compromise as the compounding failure of sprinkler control, an open unit door, and an open stairway door, all occurring together. The study finds the combined probability of that sequence a small fraction of a percent per fire event.

The IAFF's position statement makes a specific charge here: proponents of single-stair reform have not produced research on how adding floors affects egress performance, and have not analyzed the operational effect on fire department response. That data gap does exist. NFPA is actively trying to close that gap in order to properly analyze the building type.

See Appendix 1, Argument 1

Firefighter Safety in Single-Stair Apartment Buildings: Access, Egress, and Rescue Operations

Firefighter safety deserves equal weight in this argument. Firefighters are the ones who extinguish the fire, and the ones relied on to reach anyone who can't get out on their own. The heroes in any fire scenario. Apartment building design needs to let them do that job efficiently and safely, because rushing down a smoke-filled hallway toward a fire is already a leap of faith that the building's protection systems are holding.

Firefighters use a stair to connect hoses to standpipes and advance them toward the fire, and that same stair doubles as their place of retreat. They rely on a second stair for two reasons: to stage firefighting and rescue operations without impeding occupant egress, and to keep an alternate route open in case fire or debris blocks the way back to the stair. But staging operations on the fire floor can block that stair for anyone who hasn't evacuated yet or can't evacuate unassisted. Firefighters in full turnout gear and SCBA tanks take up real space on a landing, and once hoses cover the floor, getting past them becomes its own hazard. An enlarged landing at each floor alleviates this two ways at once: it gives firefighters more room to stage, and it gives anyone who can't manage the stairs without assistance, a protected place to wait, while reducing the congestion between egressing occupants and operating crews.

Being cut off matters most in large apartment buildings, where fire can spread through paths firefighters can't see. In a small single-egress-stair building, staging firefighters are never more than 20 feet from an apartment door, which sharply cuts the odds that an unseen fire traps them. That same short distance lets a hose stream reach the fire in the apartment directly from the stair, a capability larger buildings simply don't offer.

Practical Takeaway: Fire Safety Design Principles for Reduced Risk in Single-Stair Apartment Buildings

Point Access Blocks built per current codes mitigate the specific hazards that made Dykeman Street, Grenfell Tower, and Twin Parks North West deadly, open shafts and doors that didn’t close. That is true for all apartment buildings meeting code, regardless of the number of stairs. What is left after those hazards ae address is a single point of failure that has shifted, not eliminated; smoke-filling the corridor, not fire blocking it. The more time a person spends in that corridor, the more risk that person faces.

Code evolution by adding protection systems does not explain all of it. The next chapter provides information on how these systems prevent what actually kills someone in a fire, and why the answer has almost nothing to do with how many stairs a building has.

Fire Life Safety: Preventing a Fire from Affecting People

Fire Prevention Design: Sprinkler Systems and Stopping Ignition Before It Becomes a Life Safety Threat

Fire prevention starts with a simple principle: stop ignition from ever becoming a threat to the people in the building. The report the Minnesota Department of Labor and Industry commissioned from an independent fire protection engineering firm found no fatalities beyond the room of fire origin in sprinklered buildings across the incident data from Minnesota it reviewed. Fire spread and smoke spread caused zero fatalities outside the apartment where the fire started. The flipped candle, the grease fire on the stove, the cigarette on the mattress, sprinklers controlled every one of them.

NFPA incident data on sprinklered home fires backs this up. When a sprinkler system activates, a single head extinguishes or controls the fire roughly 85 percent of the time, and activating an additional head covers most of what remains, pushing control past 95 percent. Full-scale fire spread inside a sprinklered unit, the kind that would threaten a corridor or a stair, is rare enough to be the exception, not the risk that needs to be designed around.

Automatic Sprinkler Systems and Fire Code Compliance in Point Access Block Design

NFPA data on fire incidents shows sprinklers controlling fire spread in the significant majority of apartment building fires, most often with a single sprinkler head. Sprinklers don't just knock down flame. Their cooling effect also reduces how much smoke a fire can generate and spread. Smoke moves because of pressure the fire creates and the temperature difference between the fire and the surrounding air; hot air moves toward cold, and that pressure differential drives smoke into corridors and stairwells. By cooling the fire, sprinklers shrink both the pressure difference and the temperature difference driving that migration, which means less smoke gets produced and less of it spreads.

Ensuring the sprinkler system continues to be available to provide protection is the number one measure in fire/smoke events. System monitoring is a key in ensuring it remains that measure of safety.

Compartmentalization as Fire Safety Design: Code Requirements for Multi-Family Buildings

Compartmentalization means building a series of fire-rated walls and floors that separate fire from egress routes, slowing fire and smoke enough to give occupants real time to escape. Apartment buildings and hospitals both lean on this strategy to protect occupants. Each apartment unit sits inside a one-hour-rated box, except at the corridor wall, and the corridor itself sits separated from both the units and the stair. That layering forces a fire to cross two fire-rated doors before it can threaten the stair, and it puts an intermediate buffer space, the corridor, between likely fire locations and the one path everyone needs to reach.

This layered system is what actually protects occupants in an apartment building; it keeps the fire separated from the stair. Dykeman Street never had it. Propped-open doors compromised it at both Grenfell Tower and Twin Parks Northwest. And all three buildings shared one more thing in common: none of them had a sprinkler system.

Numbers to Consider for Life Safety in Point Access Block Design

Two numbers frame a key aspect of safety in PABs: 10x and 250 feet.

Code-allowed large two-stair apartment buildings, despite adding only one extra stair, produce roughly 10 times more fires affecting 10 times more people than small single-stair buildings do. This is based on 4 units and 4,000 s.f. limit for single stair buildings versus 40 units in 40,000 s.f. allowed for Type III-A construction. This does not even account for how many units are at the end of the single corridor, beyond the end stair. I have seen as many as 7 units beyond the end stair, effectively having only one means of egress. These can occur at each end of the corridor, every floor.

Long, smoke-filled hallways lead to crowded stairs in these buildings, especially once firefighters claim one stair for firefighting and rescue operations and push everyone else toward the other. That bottleneck slows egress for the entire building, not just the floor where the fire started. A National Institute of Standards and Testing (NIST) report notes that the occupant flow down the stair slows by 25% at each floor where a steady stream of people flow into the stair. Think of the bottleneck at every freeway on-ramp from merging traffic.

250 feet is the exit access travel distance the code allows in apartment buildings, measured from any point in an apartment to the closest stair. In practice, that can mean walking over a hundred feet down a smoke-filled hallway before reaching that stair, and further still if that stair is over-crowded and you want the second one. That same distance raises firefighter risk: a fire can flare up behind them, cutting them off from the stair and from each other. Small single-egress-stair buildings hold that maximum corridor travel to 20 feet, the length of your living room.

Less distance means less potential for a fire to affect you, and less exposure to smoke if it does. You can hold your breath for 20 feet.

Tech Point: Speed of Familiarity

A 2025 agent-based simulation study in Sustainability (Wang, Shi, Che, and Xie, "The Dominant Role of Exit Familiarity over Crowd Interactions and Spatial Layout in Pedestrian Evacuation Efficiency") shows familiarity should be the controlling variable, rather than one input among several. The model tested exit familiarity across three information conditions: occupants who know the exit's exact location, occupants who know only its general direction, and occupants with no exit information at all. Average evacuation time rose from roughly 300 time steps with full exit knowledge, to roughly 450 to 470 with partial knowledge, to roughly 9,500 to 9,600 with no exit information.

Moving confidently to a known stair is faster than moving toward a stair with partial knowledge, or no knowledge at all. The possibility that occupants do not know where the stair is, especially on upper floors where people primarily use the elevator, results in more time in a smoke-filled corridor, in worsening conditions. Exit signs are not enough. Airplane style lighting and distinct door color can be a significant time saver in two-stair buildings, but not needed in PABs.

See Appendix 2, Item 2

Practical Takeaway: Fire Safety Design Principles of Reduced Probability and Exposure

Point Access Blocks combine two forms of protection that most people evaluate separately. They reduce the probability that a fire ever threatens a person outside its unit of origin, through compartmentalization and sprinklers working together. And they reduce exposure when a fire does escape, through shorter travel distances and less congestion at the stair, compared to a large two-stair building with many more people and where more units can have a single point of failure at the end of a long corridor. A worse condition that is code compliant, less safe than what PABs propose as equivalency. Reduced probability and reduced exposure aren't two separate arguments. They're the same design principle applied twice, and together they make the safety case.

Prevention and containment explain most of the story, but they don't explain all of it. The next chapter turns to what happens on the rare occasion protection fails: what actually kills someone in a fire, how fast that danger closes in, and why the answer has almost nothing to do with how many stairs a building has.

Fire Safety Design and Life Safety Science: Why People Die in Apartment Building Fires

The Blunt Science

I have already asked you to switch one question for another. Instead of "how do I escape," ask "how do I prevent exposure to a fire or smoke hazard." The reframe is necessary once you understand exposure the way a fire professional does: as a function of hazard intensity, concentration, and time, not as a binary condition you either encounter or don't. This chapter builds that understanding, based on the physics.

Three variables govern whether a person in an apartment building fire lives or dies. First, what the fire and its combustion products actually do to the human body, which turns out to be more than most people assume. Second, how long a person is exposed to those products before reaching a survivable space, a function of walking speed, egress geometry, and the queuing behavior of crowds at bottlenecks. Third, whether the physical systems meant to keep smoke where it started, compartmentation working with pressure and buoyancy, actually hold. Layer a correlated timeline of fire department response on top of all three, and you get an in-depth picture of why some fires kill and most don't.

Smoke Inhalation, Not Fire, Is the Leading Cause of Death in Apartment Building Fires

Start with the most basic fact in fire science, fire doesn't usually kill people. Smoke does.

The U.S. Fire Administration's (USFA) own fatality data makes this plain. Looking at residential fire deaths where investigators recorded cause of death, smoke inhalation alone accounts for about 35 percent of fatalities. Thermal burns alone account for about 6 percent. Add the cases where both were present, and burns and smoke together explain roughly 89 percent of residential fire deaths. Cardiac arrest, mostly from the strain of trying to escape, accounts for another 4 percent.

Toxicity of Smoke

The mechanism behind that number is worth understanding, because it's what a protection strategy actually gets designed around. Structure fires today burn a fuel load dominated by synthetic polymers, polyurethane foam in furniture, PVC in wiring and finishes, engineered wood products bonded with resins, and that fuel package produces a very different smoke than the cotton and wood fires the fire service trained against a generation ago. Combustion under the oxygen-starved, under-ventilated conditions typical of a modern, tightly sealed compartment produces disproportionately more carbon monoxide and hydrogen cyanide per unit of fuel consumed than well-ventilated flaming combustion does. That matters because it's exactly the condition a closed apartment creates: door shut, fire growing, oxygen depleting, combustion becoming progressively less complete and more toxic. It's also why most fire deaths happen in or near the room of origin when a fire stays contained, a pattern the Twin Parks North West case below breaks in an instructive way.

Carbon monoxide does its damage through simple chemistry. It binds to hemoglobin with an affinity roughly 200 to 250 times greater than oxygen's, so even a modest concentration in the air steadily converts a person's blood into a transport system that can no longer carry oxygen to the brain and heart. The clinical picture tracks the percentage of hemoglobin converted to carboxyhemoglobin: a saturation of 10 to 20 percent produces headache and early impairment of judgment and coordination, 30 to 40 percent produces confusion, nausea, and marked loss of coordination, and above 50 percent, loss of consciousness becomes likely. Concentration and duration drive how fast a person moves through that progression, and in a fire atmosphere heavy with combustion byproducts, that progression can move very fast. None of it requires flame contact. It only requires breathing. According to a Cleveland Clinic report, 2-3 breaths of this will cause incapacity from coughing and lack of oxygen.

Fire protection engineers don't model toxicity as a single gas in isolation, because a real fire atmosphere is a mixture, carbon monoxide, hydrogen cyanide, depleted oxygen, elevated carbon dioxide, that acts on the body cumulatively. The standard approach, laid out in ISO 13571 and the Society of Fire Protection Engineers (SFPE) Handbook, used throughout the industry, calculates fire concentrations, or FEC and FIC: a running tally of accumulated exposure to each species relative to the dose known to incapacitate a healthy adult, added together. The fire concentration framework is additive and cumulative by design: a few minutes at a moderate concentration can cross that threshold just as certainly as a shorter exposure to a spike can, which is exactly why the duration question in the next section matters as much as the presence question in this one.

Visibility in Smoke

A visibility problem layers on top of the toxicity, and it compounds the danger rather than running alongside it. Smoke is fundamentally a suspension of solid and liquid particulate that scatters and absorbs light. Fire engineering literature, most notably Dr. Tadahisa Jin's foundational visibility research incorporated into the SFPE Handbook, characterizes the relationship between particulate density and how far a person can see through it. In a small enclosed space like a corridor, common guidance treats roughly 15 feet of visibility as the tenability limit, below which way-finding and safe egress become unreliable; in larger spaces the threshold extends further, around 30 feet, because occupants have more room to navigate by memory and light-source location. Below those thresholds, occupants routinely slow to a near stop, and unfamiliar or irritant smoke frequently makes people turn back toward where they came from rather than press forward into conditions they can't see through. Smoke laden with acrolein and formaldehyde, common combustion byproducts of synthetic materials, also irritates the eyes and respiratory tract directly, forcing involuntary blinking and tearing that degrades vision independent of the smoke's optical density.

Twin Parks North West, a high-rise in the Bronx, makes all of this concrete at once. The fire started in a bedroom, likely from a malfunctioning space heater, and firefighters knocked it down inside the apartment fairly quickly. The fire, in the narrow sense of flame and burning material, never traveled much past the unit of origin. Seventeen people died anyway. Smoke killed every one of them.

The Black Swan Scenario: When Every Layer Fails at Once

Twin Parks North West was a worse-case scenario, a black swan event, which two stairs did not prevent from occurring. We need to look at those failures and how we may be able to prevent it from occurring again.

The scenario that matters is specific, not general. It isn't "a fire happens." It's three separate failures stacking on top of each other at the same time: the sprinkler system fails to control the fire, the unit door where the fire started is left open, and the stairway door on that floor is also left open. Only when all three are true at once does a single stairway lose ground a second stairway would have held. Two of those three failures are unlikely on their own, and stacking them compounds that unlikelihood rather than adding it.

Start with the numbers already established. Sprinkler systems fail to control a fire outright in roughly 12 percent of activations, the flip side of the 88 percent observed reliability figure documented. Even folding every one of those failures into the data, NFPA field statistics on sprinklered home fires show that 96 percent of all such fires, failures included, still stay confined to the room of origin. Only about 4 percent cross into the rest of the unit. For smoke to reach the stairway at all from there, it still has to cross the unit's own rated entry door, meaning that door was left open at the moment smoke was forming, and then cross the stairway door as well, meaning that door was left open too. No single national statistic tracks how often both doors happen to be open at the same moment during an active fire, because the event is rare enough that incident reporting doesn't isolate it as its own category. But stack a low single-digit breach rate against two more conditions that both have to be true simultaneously, and the honest answer is that this scenario is uncommon enough that most single-stair buildings will operate for their entire service life without ever producing it. This did happen at Twin Parks North West, an unsprinklered building with many doors propped open. Here, the second stair did not help.

Where Protection Measures Fail

The building's built-in protection measures, sprinklers and compartmentation, can fail to protect everyone. Three versions of this scenario are worth naming specifically, because each one calls for a different kind of answer.

● The first is the scenario people picture first and worry about most: fire reaching the stairway enclosure itself, the one path everyone in the building depends on. This is also the scenario the building code defends against most directly, through the fire-rated stair enclosure, self-closing doors, elimination of a fire ignition source in the stair, and smoke alarms in common areas.

● The second is independent of the building entirely: an occupant who can't self-evacuate no matter how clear the stairway is, someone recovering from surgery, a wheelchair user, an occupant who's unconscious for reasons that have nothing to do with the fire. That person needs physical rescue even under otherwise normal conditions, which is exactly the population the area-of-refuge is intended for.

Opposition Point: Maintenance

The IAFF's position statement raises a systems-reliability objection: single-stair reform leans heavily on sprinklers, alarms, and compartmentation performing exactly as designed, over the entire life of the building, and the IAFF is explicit that it does not trust that assumption to hold.

Inspection and maintenance is the most critical component in ensuring these systems perform as designed, and the IAFF's statement notes that single-stair proponents offer no advocacy for improved inspection and enforcement to go along with the reduced egress redundancy.

sprinkler reliability sits around 88 percent, and only reaches roughly 96 percent where NFPA 25 and NFPA 72 inspection, testing, and maintenance programs are actually enforced. Where jurisdictions enforce ITM programs aggressively, sprinkler reliability data supports the equivalency claim; where they don't, it doesn't.

Two elements of data are missing and needed. First, jurisdiction-by-jurisdiction ITM compliance rate data specific to small, single-stair apartment buildings, as distinct from the broader sprinklered building stock NFPA reliability figures are drawn from; small buildings with thinner ownership and management structures.

See Appendix 1, Argument 3

Smoke Migration

The physics above explains exactly what happened. The door to the apartment of fire origin didn't close behind the people who fled it, and neither did the stairwell doors on multiple floors. Smoke, buoyant and pressurized by the heat of the fire, found an open path from a single unit into the stairwell, and from there, driven vertically by mechanisms this chapter covers next, into hallways many floors above and below the fire. People who never saw a flame, who were nowhere near the apartment where the fire started, breathed carbon monoxide and lost visibility in their own hallways and stairwells, crossed their own toxicity threshold before they reached the ground floor, and died there. That was a black swan event in every sense, and one that was preventable.

A fire that stays contained to one apartment doesn't automatically stay safe. If the smoke escapes, whether the flame spreads, becomes almost beside the point. This is exactly why the protection layers, sprinklers that limit how much smoke gets produced in the first place, and doors that actually close, matter more than the stair count ever will. Sprinkler activation doesn't just knock down flame; it cools the fire plume and reduces the buoyant pressure driving smoke through openings, which is why NFPA data shows fires with an operating sprinkler present stay confined to the room of origin about 96 percent of the time, compared to 74 percent for fires with no suppression system at all. Dykeman Street, Twin Parks North West and Grenfell Tower didn't have a working sprinkler system. Nobody has to guess whether that mattered.

Precisely the reason International Building Code (IBC) Section 903 requires sprinkler systems to be supervised (monitored), for assurance they continue to be available for fire protection. As we see from the data, this point is the most critical. And one of the primary reasons older existing apartment buildings need a way to be more easily relaced.

Tech Point: Pressure differentials

A study from the Netherlands Fire Service Academy showed that peak pressure in the fire room during the ordinary closed-door tests, Variant 1, reached 60 to 170 Pa. (0.24-0.68 inches of water column) Peak pressure in the fire room during the sealed, airtight, S200-gasketed tests, Variant 5, reached 340 to 1,010 Pa (1.36-4.05 inches of water column), roughly four to six times higher. The report states a higher pressure difference can push the same amount of smoke, or more, through a smaller remaining gap. Sealing the door more effectively did not eliminate the leak; in these tests it raised the pressure behind it.

The report shows that a closed door is fairly effective in preventing smoke migration to the corridor. It is when the door is open, by occupants or fire fighters, even for 30 seconds, that a significant amount of smoke can enter the corridor. Door closers, next to sprinklers and alarms, are the most critical fire protection system.

See Appendix 2, Item 3

Tenability, Egress Time, and Smoke Exposure: The Fire Science Behind Life Safety Design

Knowing that smoke is the danger only gets you halfway. The other half is dose, and dose is concentration multiplied by time. A little smoke for a few seconds is an inconvenience. The same smoke for three minutes can push a person past their toxicity limit. Time is the variable that turns "there was smoke in the hallway" into "someone died in the hallway."

Fire engineers call the point where a space stops being survivable the tenability limit, measured jointly by visibility, temperature, and toxic gas concentration. Modeling done for a recent Minnesota state study on small apartment buildings shows how fast that clock runs in practice. In its computational fluid dynamics simulations, visibility in a fire-floor corridor dropped below the 15-foot tenability criterion within about a minute of fire development, spread to roughly half the corridor by 300 seconds, and covered essentially the entire corridor by 600 seconds. Temperature crossed the 140°F tenability threshold in about 10 percent of the corridor at 300 seconds, growing to half the corridor by 600 seconds, with carbon monoxide following a nearly identical curve. A hallway that's walkable at second 30 can be unsurvivable by second 90, and thoroughly untenable well before the ten-minute mark most fire departments are targeting for a full first-alarm response.

Set against that clock is how fast a person can actually move, and movement speed isn't a fixed number, it's a function of population, density, and conditions. Engineering data compiled in the SFPE Handbook, drawing on Fruin's original pedestrian movement research and subsequent work by Predtechenskii and Milinskii, puts unimpeded walking speed for an alert, mobile adult on a clear, level surface at roughly 1.2 to 1.4 meters per second, call it four feet per second. That number drops fast under real fire conditions. Below the 15-foot visibility threshold, occupants typically slow markedly, feeling for walls and door frames rather than walking normally; below about 10 feet, many people effectively stop making forward progress at all. Descending a stairway is slower still than walking a level corridor under any conditions, the biomechanics of controlled downward stepping cap most adults at somewhere around 60 to 70 percent of their level walking speed, before smoke, panic, or unfamiliarity even factor in. Occupants with reduced mobility, elderly residents, people using a cane or walker, a parent moving young children, sustain even slower speeds, sometimes a third of the unimpeded rate.

Density adds a second penalty on top of individual speed, and this is where geometry and occupant load start to matter as much as raw walking ability. A stairway or doorway has a maximum specific flow, a ceiling on how many people per minute can pass through a given width of exit regardless of how fast any individual wants to move. When people arrive at a stair door faster than that discharge capacity can clear them, a queue forms and keeps growing for as long as arrivals outpace departures, the same fluid-dynamics-style bottleneck anyone who has left a stadium through one gate instead of four has already experienced. A small single-stair building with sixteen to twenty-four total occupants feeding one stair rarely generates a queue at all; arrivals spread out in time and never approach the door's capacity. A larger two-stair building, especially once fire department operations claim one stair for hose lines and staging, can put eighty, a hundred, or more occupants onto a single remaining path simultaneously. A surge of eighty occupants converging on one door doesn't clear in seconds. It queues, and every person waiting in that queue keeps accumulating exposure while waiting.

Practical Takeaway: Fire Safety Design Principles for Exposure Risk in Apartment Buildings

Fire itself rarely escapes a sprinklered unit, the data shows that. What's changed is what you are up against when it does. You face hotter, faster, more toxic smoke from synthetic materials than fire science assumed a generation ago. Point Access Blocks answer that shift directly, not by making fire less likely (sprinklers already do that) but by making the corridor short enough to cross in a single held breath.

Knowing the primary cause of death and injury in today’s fires helps us to determine ways to prevent exposure to those hazards. The next chapter turns to how PABs provide the building geometry that reduces exposure to these hazards, and it has nothing to do with the number of stairs..

Point Access Blocks: Protection Measures that Protect People

Reducing Exposures to Hazards

Time is the metric that measures our risk in a fire. The longer we stay exposed to the hazard, the less likely we are to get out. Time and risk go up together. Meaning that any means that reduces time will reduce risk to your health. There are human factors and building factors that can reduce the risk.

Human factors include confidence in exit path, which reduces hesitancy and speeds egress time. Familiarity and education are two primary means to influence huma factors in reducing risk.

Building factors include reduced distance one must travel to safer conditions, primarily the stair. Building factors also include means for different people to be able to egress at different speeds, based on their abilities, without significantly reducing the egress of others.

What a Study Showed

The same study's modeling gets more specific once you break it out by building type and door position. In the code-compliant two-exit building, with the unit door closed, the fire-floor corridor stayed tenable for roughly 10 minutes if the fire started in the unit nearest the stair, but only about 5 minutes if it started in a unit near the center of the floor, farther from the stair the corridor's own smoke has to travel to reach. Leave that unit door open, and corridor tenability barely moved, staying around 10 minutes, but the stairway itself went untenable in about 3 minutes, because the shaft was now doing the job the door was supposed to prevent. In the smaller single-exit buildings the study modeled, the equivalent unit fire reached corridor tenability in about 2.5 minutes regardless of whether the door was open or closed, and a corridor fire involving a micromobility battery, the modern e-bike and e-scooter ignition source now showing up in fire service data, reached tenability in about 30 seconds in these buildings, versus roughly 90 seconds in the larger two-exit building. Smaller volumes fill with smoke faster in absolute terms.

What that number needs paired with it is how fast people actually clear the floor, which the same study modeled separately using occupant movement software. The two-exit building took 5 to 7 minutes to clear its fire floor. The single-exit buildings the study modeled, from a 4-story code-compliant building to an 8-story prototype, cleared theirs in 30 seconds to a minute. Set movement time against tenability time for each building on its own terms, and the two-exit building has occupants moving for 5 to 7 minutes against a corridor that holds for roughly 5 to 10 minutes, a real but narrow margin. The single-exit buildings have occupants moving for well under a minute against a corridor that holds for about 2.5 minutes, a proportionally wider margin, even though their corridor fails sooner on the clock in absolute terms. Smaller isn't just faster to evacuate. It's faster to evacuate by more than it's faster to fill with smoke.

Time to Egress Matters

Grenfell Tower delivers the hard lesson in what happens when exposure time stretches instead of shrinks, through a different mechanism than queuing but the same underlying variable. The fire started outside the building, in combustible cladding on the exterior, and climbed the facade far faster than anyone expected. Official guidance at the time told residents to stay in their apartments rather than evacuate immediately, a strategy that depends entirely on the building's compartmentation holding. When it didn't, and smoke began working into stairwells and corridors, residents who had followed the guidance stayed in place for a long time, while conditions around them deteriorated far past any tenability limit measured in minutes.

You don't need a facade fire or a stay-in-place policy to see this principle at work in ordinary code minimums. A large two-stair apartment building allows up to 250 feet of travel from a place in an apartment to the nearest stair. At an unimpeded four feet per second, that's over a minute of walking under good conditions, before accounting for slowed movement in degraded visibility or a queue at the door. A small single-stair building typically holds that distance to a fraction of it; twenty feet is a five-second walk even for someone moving slowly, short enough that most people could hold their breath the entire way. Measured against a tenability clock, speed saves lives.

Tech Point: Stay or Go decisions

A more consequential effect of familiarity with the stair doors is not just on speed, but on the decision itself. An occupant who is confident of the route, because there is only one, or because the second stair is one they actually use regularly, can make the self-evacuate decision quickly once the alarm sounds. An occupant who is uncertain where the stair is, let alone a second stair, faces exactly the kind of ambiguity the Dutch report's cited behavioral literature associates with delay: people who are uncertain tend to gather more information, check on others, or default to the route they already know before committing to move, even when that route is compromised.

The decision to self-evacuate quickly is not just based on familiarity, but also the familiarity by those around them. If the neighbors are headed quickly to a stair, they will follow. An occupant who does not know, or does not trust, where the stair is, has no reason to choose to self-evacuate through a corridor that may have smoke in it over staying behind their closed door.

For a single-stair PAB, this ambiguity is structurally smaller on both counts. There is no second stair to be unfamiliar with, it is the same short, known path everyone already uses. For a two-stair building at the 40,000 sf, 200-occupant scale, the familiarity gap is a real, cited, and currently unaddressed cost against the redundancy that stair count is assumed to provide.

See Appendix 2, Item 2

Self-evacuation is the Priority

Now overlay the fire department's own timeline, because it explains why occupant self-rescue within that first survivable window matters more than most people assume. NFPA 1710, the standard career departments are measured against, sets a benchmark of roughly 80 seconds turnout time and 240 seconds travel time for the first-arriving engine, a total response time around five and a half minutes for 90 percent of calls, assuming an already-staffed career department. Getting the full first-alarm assignment on scene, the additional engines, ladder trucks, and command staff needed to simultaneously fight the fire and conduct primary search, takes a full eight minutes of travel time under the same benchmark, pushing total elapsed time from ignition detection toward the nine or ten-minute mark even in a well-resourced department. Rural and volunteer departments, which the Minnesota study specifically flagged, can run response times several multiples longer, with some remote departments needing up to thirty minutes to get even a first unit on scene.

Put that next to the tenability clock and the picture is stark. A corridor that loses visibility within sixty seconds, and becomes largely untenable to carbon monoxide within five to ten minutes, reaches that state in most jurisdictions before the full firefighting assignment has even arrived, let alone advanced a hoseline and knocked the fire down. Occupants who make it out do so almost entirely on their own effort, within the tenability window, before help arrives. That's not a criticism of the fire service, whose response times reflect physical distance and staffing constraints that building design can't fix. It's the reason building design has to do the work instead: shrink the travel distance, shrink the queue, and you shrink the portion of that unforgiving first several minutes that any given occupant has to survive.

The tenability clock highlights that safety is based on time. Protection measures like smoke detection, emphasize that point. Reducing the time to egress will help the most people most of the time.

When Fire Containment Fails: Compartmentation, Stack Effect, and Building Code Design

The first two scenarios assume something: that smoke escaped the apartment where the fire started, and that it built up enough to matter over a meaningful stretch of corridor. Neither of those things is supposed to happen, but it does. Apartment buildings are built around a specific idea called compartmentation, boxing a fire into the unit where it started, using rated walls, rated floors, and self-closing doors, so it never becomes anyone else's problem. When that system works, the first two sections barely come into play. When it fails, they become the whole story, and understanding exactly how it fails requires a bit of building physics.

A fire compartment doesn't just get hot, it pressurizes. As combustion heats the air and gases within a closed room, that gas expands, and the compartment develops a positive pressure relative to the spaces around it, concentrated near the ceiling where the hottest gases collect. Open a door connecting that compartment to a corridor, and you don't get a simple one-directional flow of smoke outward. You get a two-layer, bidirectional exchange: hot, buoyant smoke pushes out through the upper portion of the doorway opening, while cooler air is simultaneously drawn in along the floor to replace it, the two flows separated by what fire dynamics literature calls a neutral plane. That's exactly why a self-closing door matters so much more than its modest physical presence suggests. Close that opening, and the pressure-driven exchange that would otherwise fill a corridor within a minute or two collapses to whatever leaks through the door's perimeter gaps, typically modeled at well under a square foot of open area, an entirely different order of magnitude.

Field research confirms this isn't just theory. The Dutch Fire Service Academy ran nineteen full-scale fire tests inside a real residential building with internal corridors, instrumented with gas and visibility sensors throughout, and measured the effect of door position directly rather than modeling it. With the fire-room door closed, peak pressure in the fire room ran 60 to 170 pascals; sealing the compartment tighter, simulating newer, more airtight construction, pushed that peak to 340 to 1,010 pascals, confirming that a fire compartment's pressure buildup is a real, measurable, substantial force pushing against whatever opening it can find. The tests also isolated exactly how much door-open time it takes to matter: opening the fire-room door for just 30 seconds, then closing it again, produced a corridor condition nearly identical to leaving that door open for the entire test run, an impaired-escape condition within about 5 minutes either way. A door doesn't need to fail outright to compromise a corridor. It needs to be open for about half a minute at the wrong moment, which is a far lower bar than most code discussions assume.

Vertical shafts amplify that same buoyancy effect through a mechanism known as stack effect. A stairwell running the height of a building behaves like a chimney whenever a meaningful temperature difference exists between the air inside the shaft and the air outside the building, which describes most climates for most of the year. In cold weather, warm air inside the stairwell becomes more buoyant than the cold air outside, so the shaft develops a pressure gradient that pulls air in at the bottom and pushes it out at the top, the same draft that makes a fireplace flue work. Introduce smoke into that stairwell at any point below its midpoint, and stack effect actively pulls it upward through the shaft, independent of anything the fire itself is doing. The taller the building and the colder the outside air, the stronger that draft becomes.

Dykeman Street shows what happens when there's no compartmentation to interrupt either mechanism, not just a failure of one instance of it. A cigarette dropped into cardboard boxes started a fire near the base of a central stairwell that ran open, floor to floor, with no enclosure separating it from the building's hallways. No sprinkler system controlled the fire early, and no rated separation slowed either the pressure-driven flow out of the fire area or the stack-effect draft up the open shaft. The stairwell did precisely what an unenclosed vertical shaft does in a fire: it fed the buoyant plume more air the higher it climbed, accelerating combustion at the same time it accelerated smoke movement, a self-reinforcing chimney effect with nothing built into the structure to interrupt it. That building didn't have a single-stair path that failed. It had no meaningful separation between any of its parts, functioning in a fire as one continuous, connected volume from the ground floor to the roof, exactly the geometry stack effect and plume buoyancy exploit most effectively.

That comparison matters, because it's easy to hear "single stair" and picture Dykeman Street. They're not the same thing. A modern compartmented building with one well-enclosed, rated stairwell interrupts both the doorway pressure exchange and the stack-effect draft at every floor, bearing almost no resemblance, in a fire, to an open shaft with no rated separation and no sprinklers at all. The stair count was never the variable doing the work in that fire. The absence of any containment system was.

Even where the systems exist on paper, they only work if someone keeps them working, a maintenance and inspection problem more than a design problem, and a solvable one. Fire incident data on sprinkler systems shows an observed reliability, meaning the system actually flowed water when called on, of around 88 percent. The inspection and testing programs required under NFPA 25, and the parallel programs NFPA 72 requires for detection and alarm systems, push that number toward 96 percent when jurisdictions enforce them. The gap between those two figures isn't a mystery waiting on new technology. It's someone checking a valve on a schedule instead of skipping it, which is also exactly why risk modeling for the Minnesota study attributed roughly 97 percent of comparative fire risk across every building geometry tested, one stair or two, to whether the sprinkler system flowed on demand. Get that single system right, and most of the risk that modeling identified disappears, regardless of how many stairs the building has.

Practical Takeaway: Designing Apartment Buildings for Reduced Smoke Exposure, Not More Exits

Put the three points together and a single design principle emerges. Smoke is what kills you, so stop it from forming and spreading in the first place, using suppression that cools the plume and doors that interrupt the pressure-driven exchange at a door opening. Time is what turns smoke into a fatality, and that clock runs faster than most fire departments can beat, so shrink the distance and the queuing delay between a fire starting and a person reaching safety. Containment is what makes the first two points hold over the vertical extent of a building, so build systems that interrupt stack effect and buoyant flow at every floor.

None of that argues for more exits. It argues for less exposure, less smoke produced, less time spent in it, less chance that a single failure turns a contained fire into an uncontained one. It does depend on doors — closing, and staying closed — more than this book's design case sometimes implies elsewhere; that dependency doesn't go away with fewer stairs, it just gets concentrated onto fewer doors that are correspondingly easier to inspect and maintain. It also tells you exactly what to check the next time someone claims a building "only has one stair," as if that fact alone settles the question. Ask what's producing the smoke. Ask how long someone would actually be exposed to it. Ask whether the doors and the systems behind them are maintained, not just installed. Those questions get you closer to the real risk than the stair count ever will.

Understanding why people die and how fast the danger closes in explains the mechanism. It doesn't yet give you a way to make the case to the people who approve building permits. The next chapter turns this science into an argument you can actually bring into a code hearing, backed by real buildings, real response-time data, and a checklist you can use tomorrow morning.

Point Access Block Fire Safety Equivalency: The Egress System

The Argument

Chapter 1 introduced a fear: that a single stair means a single point of failure. Chapter 2 dismantled the mechanism behind that fear: smoke, not stair count, harms people; exposure duration determines whether smoke turns fatal; and reducing the probability of a fire affecting people in the first place. That's the evaluation process we have walked through so far.

Making the case for equivalent protection to large two stair buildings doesn't require winning every point, but where it matters most, the vast majority of the time. It requires three specific claims, each backed by something concrete, and a short list of design features you can point to on a set of drawings. This is how PABs get approved.

What the Numbers Show

Before we start on how many are egressing and the conditions they could face, some number on who is mostly affected by fire in any apartment building. The numbers reported by firefighters through their reporting system, primarily NFIRS, and collated by NFPA, show that most injuries and fatalities occur in the apartment where the fire occurred.

The vast majority of fires start in an apartment, typically by cooking, smoking, candles, or some other occupant initiated device. Much more rare is the electrical fire or system ignition. The data shows that the majority of injuries occur to these people, and only a percentage occur outside of the apartment of ignition.

Where Protection Measures Fail

● The third is the compounding failure chain itself: sprinkler failure, propped unit door, propped stairway door, all at once, filling the only interior stairway with smoke while people are still on upper floors. The very rare black swan event, where everything fails. Thankfully very rare, but also one the building code cannot prevent.

Fire Risk Probability and Egress Time in Single-Stair Versus Two-Stair Apartment Buildings

Risk isn't one number. It's the product of several: how likely something bad is to happen, how severe it is if it does, and how long you're exposed to it. Most redundancy arguments focus only on the middle and last terms and treat the first as fixed. A small single-stair building improves all three simultaneously, and the way it does so is worth walking through with actual probabilities rather than asserting it.

The risk-informed methodology the Minnesota study used to compare building geometries is instructive here, independent of whatever conclusions you draw from its specific numbers. It builds an event tree: given a fire ignition (treated as a certainty, probability 1.0, to isolate the performance of downstream systems), what's the conditional probability the sprinkler fails to control it, and given that failure, what's the conditional probability the unit door is also left open, and given both of those failures, what's the conditional probability the stairway door on the fire floor is also open. Only when all three failures stack does a single-stair configuration lose an advantage a two-stair configuration would have retained. This is what happened at Twin Parks North West, doors to both stairwells were propped open. With an observed sprinkler reliability around 88 percent, meaning roughly a 12 percent chance of the first failure alone, and each subsequent conditional probability in that chain smaller still, the compounded probability of the full failure sequence works out to a small fraction of a percent for any individual fire event. That's not an opinion about single-stair safety. It's what happens when you multiply probabilities that are each already small.

The exposure side compounds the same arithmetic. Fewer units per floor means fewer occupants converging on any single point of egress, which keeps arrivals at the stair door under its discharge capacity and prevents the queuing delay Chapter 2 described, which also means the stairway door is not consistently open by people passing through it.. Shorter travel distance means less time inside a corridor whose tenability clock starts running the moment smoke escapes its compartment. Multiply a low probability of exposure occurring at all by a short duration on the rare occasion it does, and the result isn't a building that got lucky. It's a building where luck stopped being the load-bearing variable.

Run that arithmetic against real modeled numbers, not just the general principle, and the gap is stark. The same Minnesota study modeled occupant movement time with egress simulation software across every building geometry it evaluated. The code-compliant two-exit building took 5 to 7 minutes to clear its fire floor and 11-16 minutes to fully discharge every occupant in the building. Every single-exit configuration the study modeled, from a modest 4-story building to an 8-story prototype with twice the floor area, cleared its fire floor in 30 seconds to a minute, and fully discharged in 2.5 to 5 minutes. Widening the single-exit stair from 44 inches to 48 inches, a real cost difference in construction, made no measurable difference to any of these times, evidence that stair width past the code minimum isn't where the exposure-time advantage comes from. Geometry is. Fewer units, shorter halls, and a stair every occupant already walks past daily turn a fire-floor clearance time measured in minutes into one measured in seconds.

What Historic Building Fire Data Shows, and Doesn't Show

New York City has permitted small multiple-dwelling buildings served by a single stair for years, under specific conditions: dwelling units per floor, sprinkler coverage, construction type. These buildings exist across the five boroughs, and they operate today under active fire code enforcement. If a fundamental defect in the single-stair concept were producing a steady pattern of fires that outgrew their protection systems, they would have surfaced by now.

Seattle's building code has permitted single-stair apartment buildings up to six stories for nearly 50 years now, under its own set of conditions: sprinklers, pressurization to counteract exactly the stack-effect draft Chapter 2 described, and unit limits per floor. Two different cities, two different climates, two different code administrations, and the same underlying answer: when the protection systems are in place, enforced, and the occupant loads stay within the geometry's intended capacity, the stair count stops being the variable anyone worries about a few years in.

What the evidence does not show, across all apartment buildings, is the number of rescues required. This is where firefighters become concerned. In apartments, where more people are living in the same space, and more people are increasingly aging, or being physically limited, rescues are becoming an increasing hazardous position for firefighters. This is a major concern, for all apartment buildings, one-stair or two. The question then becomes, what can truly help people and firefighters in a fire, or other natural disaster?

Opposition Point: Contra-flow

The IAFF frames this as a collision of two groups moving in opposite directions through the only available path: residents evacuating down while fire fighters advance up, each group slowing the other exactly when speed matters most. Connecticut's Uniformed Professional Fire Fighters Association put it in operational terms when opposing that state's single-stair proposal: fire fighters and residents moving in opposite directions on the same stairs is inherently hazardous, and would require heavier reliance on aerial ladders and window rescues to compensate.

Every fire fighter who has staged on a landing while residents are still coming down knows this isn't theoretical. Turnout gear and an SCBA tank roughly double the floor area a person occupies, hoselines cover the stair once charged, and a single shared path means every one of those obstacles sits directly in the way of anyone who hasn't gotten out yet. In a large two-stair building, the second stair gives responders a dedicated route that doesn't cross occupant flow. A single-stair building has no such option by design.

In theory this works great. But when firefighters arrive, people are naturally using both stairs. Both stairways are full of people evacuating. Once firefighters choose a stair to use for their operations, they now need to clear the stair. In a large apartment building, there would likely be 4x-5x the number of people using that stair (20 occupants/floor vs. 200 occupants/floor, 100 per stair).

The geometry that makes single-stair buildings fast to clear in the first place, few units per floor and a short corridor, is the same geometry that limits how much the cross-flow conflict exists.

See Appendix 1, Argument 2

Firefighter Response Time and Occupant Egress Timeline: A Combined Life Safety Analysis

Occupant safety gets most of the attention in this argument, but the same geometry that helps residents helps the people running into the building to save them. Firefighters face the identical tenability physics Chapter 2 described, just with a delayed start time and a longer exposure window built into the job itself.

Overlay the two timelines and the relationship becomes clear. A corridor's visibility typically drops below the 15-foot tenability threshold within about sixty seconds of a fire escaping its compartment, and conditions in an unsprinklered or under-suppressed space keep deteriorating from there. Against that, NFPA 1710 benchmarks a fire department's first-arriving engine at roughly 80 seconds of turnout time plus 240 seconds of travel time, about five and a half minutes of total response time including call processing, for 90 percent of incidents. The full first-alarm assignment, the additional companies needed to simultaneously attack the fire and conduct primary search, takes eight minutes of travel time alone under that same benchmark, pushing total elapsed time toward nine or ten minutes in a well-resourced career department, and considerably longer in the volunteer and rural departments that cover most of the country's land area. Even after that assignment arrives, crews still need time to size up the structure, stretch and charge a hoseline, force entry if needed, and begin an interior attack, commonly adding another one to three minutes before water actually reaches the fire.

Firefighter Timeline vs. Occupant Egress Timeline: Elapsed Time from Ignition

That timeline makes the case for shorter travel distances in a different register than previously noted. Most occupants who make it out do so on their own effort, before the fire department has even arrived. The tenability clock closes faster than most response times, however well resourced. Firefighters entering the building at minute five, six, or seven are walking into conditions that have already deteriorated past the point an occupant could safely cross them, which is exactly why their own travel distance to the fire floor, and their own path back to the stair, matters as much to their survival as it does to anyone still inside.

A second, less dramatic version of this same benefit shows at every building, not just the ones that make the news. Firefighters stage equipment, hoselines, tools, etc., on the stair landings, and each firefighter in full turnout gear and an air pack occupies roughly double the floor area an unequipped civilian does. In a large building, that staging point can sit a hundred feet or more from the apartment door. A stair twenty feet from the fire floor's farthest door isn't just a safer place to retreat to. It shortens the hose stretch and cuts the time a crew spends moving instead of fighting the fire, exactly when every minute gets measured against a clock that has already started running out for anyone still exposed.

One objection that still needs to be answered is, that a single stair forces firefighters and fleeing occupants into the same narrow space at the same time. The Minnesota study modeled this. It modeled cross-flow explicitly: occupants egressing down the single stair at the exact same moment firefighters begin advancing up it, the most conservative version of the scenario, with no allowance for the two groups timing their movement to avoid each other. Even under that condition, full building discharge for the two single-exit prototype buildings took 5 to 7.5 minutes, worse than the 2.5-to-5-minute discharge time without firefighters in the stair, but still inside the survivable window this chapter's timeline lays out, and still faster than the two-exit building's 16-minute discharge time with no firefighters in the way at all. The objection is real, but it is manageable, not a disqualifying flaw, especially when you consider the arrival time of firefighters to a building in about 5 minutes.

Point Access Block Fire Safety Equivalency: Additional Means of Safety

Provided the demographics of our communities, more and more people having health issues that affect how well people are able to self-evacuate, a consideration of how safety can be provided with a restricted means of rescue and increased demand for rescue.

There are two primary means of rescue firefighters perform, ladder or aerial apparatus rescue, through a window typically; and assist down the stair rescue. A primary factor being the further from the ground, the more likely the aerial apparatus rescue is needed.

Which brings up two primary scenarios of concern:

· The non-street facing units on upper floors, where tall ladders and aerial apparatus use is not possible

· Rescuing people down the stairs when firefighter operations are occupying the stair, with a stair door that may be letting smoke into the stair

Egress Design: Are Second Stairs Always the Answer

A second stairway can help in the first scenario mentioned above, where smoke gets into the stair. Hopefully the failure does not occur to both stairs. A second stair does nothing for the second scenario at all. and it's redundant with the third, since a fire that has already breached one rated stair enclosure has usually breached the building's compartmentation broadly enough that a second enclosure is reachable down the hall.

All three scenarios though can be helped by what is called a defend-in-place strategy. It is the strategy hospitals use, but would look different in apartment buildings. And the historic examples we have, would help.

Personal Emergency Evacuation Plan (PEEP)

Lets start with what everyone should know about their own safety. Education is the first key in occupant safety and this needs to be a part of the overall plan, for all multi-family dwelling residents. Not just a sticker on the back of the door, a personal plan.

The education component that everyone needs to have, no matter the building type, is a simple PEEP. Whether they evacuate or stay, some actions to take. When seconds count, and with self-evacuation the priority, a PEEP is a simple and effective way for more to get to safety.

Not everyone will read it, or remember it when the alarm goes off. But their neighbors may have read it, and remember it. And studies show that people will follow a neighbor if they seem to know what they are doing. Which means they act decisively.

Everyone should be provided a PEEP when they move in. The figure below is just one example.

Egress Design Options: Places to Wait, Not Just a Place to Run

What can help that person is a place to wait that is separated from the fire, separated from the smoke, and is where rescuers know to look. That is what an exterior balcony does, provide a space to stand without having to venture out of the apartment. That's what an area of refuge is, a fire-rated space, usually an enlarged stair landing, that can be reached quickly.

They both separate people from smoke and heat out long enough, until help arrives, instead of forcing them into a race against a clock they can't win. These can be built into the protection measure system of the building, the building geometry, that enhances protection.

Exterior Balconies for Occupants Who Cannot Self-Evacuate Safely

Exterior rescue balconies answer the first scenario above directly, where the short path to the stair is blocked. They are being studied in cities working through single-stair code reform right now. Chicago and San Francisco are both in active discussions, as part of their broader single-stair ordinance work, over requiring a small exterior balcony with an emergency escape and rescue opening at each unit, sized and located so a fire department aerial ladder or ground ladder can reach it without needing the interior stairway at all. California's building code already ties single-exit permission for sprinklered apartment buildings to an emergency escape and rescue opening as a condition of the reduced-egress allowance.

An exterior balcony provides better protection than an escape window: it gives an occupant a space with fresh air, physical separation from the smoke-filled interior, and visibility to arriving crews, all without depending on the interior stairway staying clear. It's a second way out that doesn't require a second full stairway, doesn't consume the floor area a second stair would, and directly answers the specific failure mode, smoke filling the only interior path, that the first and third scenario above describes.

Exterior balconies have been part of the protection measures countries around the world use in single stair apartment buildings. Whether street facing or at the rear of the building, in the required setback, these act as spaces where people can escape the smoke and be seen quickly. That is part of it, the race against the clock.

Areas of Refuge and Accessible Egress for Occupants Who Cannot Self-Evacuate

Not everyone in a building can move at the walking speeds Chapter 2 described. Someone recovering from surgery, a resident using a wheelchair, a parent with three kids under six, none of them will clear a stairwell at the 1.2 to 1.4 meters per second baseline the egress literature assumes for an unimpeded adult, and several will move at well under half of it. The redundancy argument tends to skip this group entirely, as if a second stair automatically solves their problem. In some building types it can. In apartment buildings, with their long, narrow corridors, it can't. A second stair fifty feet farther away isn't meaningfully more useful to someone who can't reach the first one quickly either, and it does nothing for the queuing delay if that second stair is also where a large share of the building's other occupants are converging.

Small buildings can build this in for people to reach quickly. The current building code does not require them in buildings with full sprinkler systems. This shows the building code’s trust in sprinkler systems for occupants unable to rescue themselves. An enlarged stair landing on each floor, rated the same as the stair enclosure itself, provides the protection for those unable to self-evacuate, those physically unable to go down the stairs un-aided. Building and fire codes already have a name and a set of requirements for this. In a four-unit-per-floor building with one stair, enlarging one landing, once per floor, in a building that's already compact, does the job, and it's the same landing firefighters will use for staging equipment when they arrive.

Areas of refuge, described above, answer the second scenario directly and the first scenario partially. An enlarged, rated stair landing gives someone who can't move fast, or can't move at all, a place to wait that isn't the fire, isn't the smoke, and is exactly where a firefighter conducting a primary search will check first. It buys time without requiring the occupant to win a race they were never going to win. The spaces have long been advocated for by accessibility experts as a means to help those who cannot go down the stair. In taller buildings, protected elevator lobbies provide the space. In mid-rise buildings, the protection is still needed.

Why Not Just Have a Second Stair

Areas of refuge and exterior rescue balconies cover the two scenarios that a second stairway only partially addresses, because long smoke-filled corridors are their own concern.

The Winecoff Hotel fire in Atlanta in 1946 was one the the events in this time period that prompted second stair requirements. More important than the second stair, was the requirement for not having the stair be open to all floors, requiring a stair enclosure. Providing a space of safety on every floor. The protection measures stair shafts have today are the prime measure we have in our buildings. They are the last chance place of safety, not the only one in apartment buildings.

Layered protection measures, sprinklers, compartmentation, quick access to stair; provide layers of protection that are effective over 95% of the time. And when they are not, the long corridor to the stairs have not always been the answer either. The sad truth is, the code is not built to prevent all fires from harming people, even if it were possible.

Time of exposure is the one constant in what causes harm to people, the less time it takes to get away from the smoke, and out of the building, the better.

It is Equivalent, Not an Exception

The building type achieves the same protection goals the code is actually after, through a different but demonstrated combination of features, backed by the same event-tree logic and tenability data the fire engineering profession already uses to evaluate any other building. This is equivalency. The number of stairs is not the goal. It is a means to an end, and the end is keeping people alive long enough to get out or be reached, on a timeline the numbers make explicit rather than implicit. Show that the end is met, and the specific means stops being an argument.

The Affordable Housing Case for Point Access Block and Single-Stair Development

None of this is just a fire-code argument. A building that can go up on a single urban lot doesn't require a developer to assemble and finance several adjoining parcels before construction can even be discussed, a process that's slow, expensive, and often impossible in neighborhoods where the land is already spoken for one lot at a time. Small buildings open the door to smaller, more local investors, people building in the neighborhood they live in, not just the ones who can carry a multi-parcel assembly on their balance sheet. That's not a side benefit to the safety case. It's the reason the safety case matters to more than just building officials. Every lot this approach unlocks is housing that otherwise wouldn't get built at all.

Focus is on urban lots, because zoning has a bigger part to play in suburban and small community lots

Practical Takeaway: A Code Compliance Checklist for Single-Stair Apartment Building Design

None of these are a menu to check off in full. They're a toolkit for closing the two gaps that are real, a fire in the stair enclosure itself, and a door that doesn't close. Without adding a second full stairway to do it. Match the tool to the gap: exterior rescue balconies and areas of refuge answer the occupant who can't self-evacuate; a full one-hour corridor rating and a maintained closer answer the door that doesn't close. A code official evaluating a PAB proposal should be asking which of these the design uses to cover which concession, not whether it has a second stair.

There are solutions. An exterior stairway, open to the air rather than enclosed, gives occupants and firefighters a path that never accumulates the buoyant smoke layer an interior route can, because there's no ceiling to trap it against. Exterior balconies serve a similar purpose on a smaller scale, letting someone move away from a fire, to fresher air, without ever entering a hallway or crossing a doorway's pressure-driven exchange zone. On some lots, a simple access tunnel to the rear yard with a fixed ladder gets an occupant out through a path nobody assumed the building had.

Look at what buys time for people. An area of refuge, the enlarged, protected landing described above, gives someone who can't move fast a place to wait. A corridor wall built to a full one-hour rating, not the reduced rating some codes allow for sprinklered buildings, adds a margin against the failure mode of compartment breach. Exterior balconies, the adopted method of Japan, for getting out of the smoke and being seen by firefighters.

Conclusion: Point Access Blocks as Equivalent Protection Under Fire and Building Code

Chapter 1 asked a simple question: stop asking "how do I escape," and start asking "how do I prevent exposure to the hazard in the first place." This question has been answered with physics and numbers. Smoke is the hazard, so control what produces it and interrupt the pressure and buoyancy that spread it. Time is what turns exposure into harm, measured now against an actual tenability clock you can compare to an actual fire department response curve, so shorten the distance between danger and safety. Firefighters face the same clock occupants do, arriving after it has already started running, so give them the same short paths. And for the people who can't move as fast as the model assumes, build them somewhere safe to wait instead of pretending a second stairwell fifty feet away solves their problem for them.

The goal has always been to demonstrate equivalent, or better, life safety protection, and building geometry does most of that work by keeping people safe long enough to reach safety. That's not a workaround. It's protection that holds up to the same standard the code is always intending, and in several respects, exceeds it.

Fire Protection Measures for Apartment Building Design: A Code Reference for Architects and Fire Officials

Protection Measure Options for point Access Blocks

In a situation where more and more people are living in the same space and where more and more people are physically limited in being able to self-evacuate. What are the elements in building safety that can help both occupants and firefighters.

The goal is to better help people get to a position of safety, and try to lessen the burden of firefighters to rescue, or at least not be in conditions that put their lives in danger as they perform rescues. The ideal is that everyone leaves the building quickly, allowing firefighters to get in and focus on getting the fire out.

What follows is a fire engineering inventory, not an argument: a survey of protection measures available to any small-to-mid-rise apartment building, single stair or otherwise, along with what each one actually does, who it helps most, and what it costs to provide. An architect, developer, or code official evaluating a specific building on a specific lot in a specific jurisdiction needs this information regardless of which side of the stair-count question they land on, and presenting it as a menu rather than a recommendation is deliberate. The right combination for a six-story building on a tight urban lot in a cold climate is not the right combination for a four-story building on a suburban lot in a mild one.

Although there is a national building code, it does not address all the concerns of urban and rural communities, and ones with differing weather and geologic conditions. Temperature and wind play a major part in smoke migration/evacuation and local effects can change what works best.

Stairs: Egress Design Options

Protection starts with the one stair. There are two options for the stair, interior and exterior. Each one has different benefits and concerns. Some of the benefits/concerns are based on environmental conditions, while others have fire life safety implications.

Interior stairs are protected stair shafts that have a 2-hour-fire-resistance rating. They are considered sacrosanct spaces with no elements that do not have anything to do with its use as a means of egress. They also contain the fire water standpipe, which firefighters connect their hoses to for fighting the fire.

These highly protected spaces are also the goal for people to reach, for separation from fire and smoke. They serve as staging locations for firefighters and a place where people will wait until they can get assistance to exit the building. They are busy places.

Exterior stairs have the advantage of being open to the sky, so will not typically contain smoke and toxic gases. There are conditions, cold, damp air, that will not want to let the smoke escape. These stairs may also not be protected from fire and smoke from a fire in the adjacent building, if it is not street-facing.

Exterior stairs will be protected from the dwelling units with the same 2-hour-rated protection as interior stairs and have a standpipe. One advantage, and disadvantage, is that since these spaces are exterior, they may be a little larger, and therefore less congested with firefighters and people waiting to get assistance.

Smoke Detection and Emergency Voice Alarm Systems: Fire Code Options for Apartment Buildings

The first principle is that people need to learn and be aware, at the earliest possible time, that there is an issue they need to pay attention to. How a fire/smoke event is detected and people are notified is key to starting the clock on tenability. In places where people sleep and can be groggy or mentally impaired, early alert and clear directions saves lives.

The earliest possible warning is also the cheapest protection measure on this list, which is part of why it comes first. Interconnected smoke detection that covers corridors, stairs, and common areas, not just individual units, gives every occupant in the building the same warning at close to the same moment, rather than waiting for smoke to reach their own unit's detector. In a building where the tenability clock in a fire-floor corridor can run out in a matter of minutes, shaving even thirty or sixty seconds off the time between ignition and occupant awareness is a meaningful, low-cost gain.

Currently in apartment buildings, the full building fire alarm system activates upon sprinkler flow. Smoke detectors in the corridors and common areas will, most of the time, activate the building-wide alarm faster. A side-effect is the possibility of nuisance alarms and apathy on evacuation. The alarm will at least wake people up and alert them that there is a possible threat, even if they have the apathy on movement.

Emergency voice/alarm communication systems, covered under NFPA 72's emergency communications provisions, go a step further by replacing a generic tone with spoken instructions, evacuate, relocate to a specific area, or shelter in place, delivered to specific zones rather than the whole building at once. A resident on the top floor of a five-story building doesn't need the same instruction as a resident on the floor where the fire started, and a voice system can say so directly, which a horn and strobe cannot. Code requires these systems only in high-rise buildings and a handful of other high-occupancy classifications, well above the size of any building covered here, but nothing prevents a smaller building from installing one voluntarily. The tradeoff is straightforward: a voice system costs more to install and requires periodic intelligibility testing, NFPA 72 sets a minimum speech transmission index for exactly this reason, in exchange for occupant instructions a plain alarm tone cannot deliver, an advantage that matters most in buildings with a wide range of occupant ages, abilities, and first languages.

This is clearly shown in evacuation tests. In a study lead by David Purser, pre-movement time was shown in decrease from 11 minutes to 4 minutes in familiar settings, and the reaction rate increased from 13% of the people began moving when the horn/strobes initiated, versus 40%-45% of the people moving toward the exit with voice annunciation. People naturally respond better to a human voice telling them what is happening and what to do.

The cost of such a system, for a small building, is about 30%-50% more. About $15,000 more, or about $1,000 per unit for a 4-story apartment building.

Egress Geometry and Areas of Refuge

Four measures address the same underlying problem, keeping a stairway or an alternate path clear of smoke, through different mechanisms, and the right choice depends heavily on climate, height, and site.

Exterior, open-air stairs sidestep the problem differently: there's no enclosed shaft for smoke to accumulate in, because there's no enclosure. These stairs would serve primarily the non-street facing units and be secondary stairs. This is a low-to-moderate-cost solution structurally, but it comes with climate exposure, a real consideration in regions with heavy snow or ice, and in some jurisdictions, aesthetic or zoning friction that an interior stair doesn't face. Two keys to making these work on the non-street facing units is that the stairs be able to be built within required setbacks and that there is a fire-protected path from the back to the street, for occupant egress and firefighter access. This can be as simple as a 3-foot-wide passageway that is lockable from the street by everyone but firefighters, for security.

Egress or rescue balconies give an occupant a protected space with outside air, physical separation from interior smoke, and a location visible and reachable by a ground or aerial ladder, all without requiring the interior stair to stay clear. Chicago and San Francisco are both actively working through code language for a feature along these lines as part of broader single-stair reform efforts, though neither has finalized a specific requirement as of this writing. These require the ability to be built within rear setbacks, have a passage to the street, and be able to be reached by a fire ladder, something a 6th floor balcony is too high for.

Areas of refuge, enlarged stair landings, gives an occupant who cannot descend quickly a protected place to wait for rescue. The IBC exempts fully sprinklered buildings from the area-of-refuge requirement entirely, so including one in a sprinklered small apartment building is an above-code measure. Increasing the landing depth from the 44” minimum to at least 74” adds about 20 s.f. to the stair size, or about 5 s.f. less per unit. The required communication device for areas of refuge in the building code is an option in this scenario, as firefighters will be in the one stair, and therefore no one will be unseen.

Requiring the stair to be on the street-facing side of the building, with an exterior window, for easier firefighter rescue access. Preferably larger than code-prescribed escape window of 5.7 s.f., these windows can be reached by an aerial apparatus truck ladder for simplified rescue from any floor, without requiring firefighters to carry to occupant down the stairs. Lessens congestion in the stair and gets people out of the building faster.

A cost comparison of these elements are:

● Exterior Stair – About $6,000 to $10,000 per story

● Exterior balcony – Varies widely depending on size, about $5,000 to $8,000 per unit

● Area of refuge – 20 s.f. min. at $300/s.f. cost, about $6,000 per story.

● Window in stair – Less than $1,000 per story, limits stair location in building design

Egress Design Options: Pressurized Stairs and Smoke Evacuation Methods

Passive smoke venting, roof-mounted smoke hatches or operable vents at the top of a stairway, relies on the same buoyancy this book has described throughout: hot smoke rises, so a vent at the top of the shaft gives it somewhere to go besides the corridor. It requires no mechanical power and no ongoing fan maintenance, which makes it attractive in budget-constrained projects, but its performance depends on a clear, unobstructed path to the exterior and can be affected by wind and temperature conditions a pressurized system isn't as sensitive to. Wind can actually stuff the smoke back into the stair and heavy, cool/moist air can prevent smoke from escaping.

Active smoke venting, by either a fan at the top of the stair, sucking smoke out, of a combination system with a fan blowing into the stair at the bottom and an open smoke vent at the top, is a system based on air changes, the manner atrium smoke evacuation systems used to be based. The free flow of air creates minimal pressure on egress doors and prevents smoke from accumulating in the stair, lessening environmental effects on smoke evacuation out the smoke vent on the roof. Fan and smoke vent sizes based on air changes per hour of air volume in stair. Connecting the fan directly to municipal power rather than a generator reduces cost.

Stairwell pressurization uses a fan system to hold the stair enclosure at a slightly higher air pressure than the surrounding floors, so smoke attempting to enter through door gaps or during door openings gets pushed back rather than drawn in. It's most valuable in taller buildings and colder climates, where that draft runs strongest. It's an engineered system and also the most expensive measure on this list to install and maintain: a dedicated fan system, ductwork, periodic testing, and in many designs a backup power source to keep the fans running if normal power fails. Here as well, the fans can be directly connected to reliable municipal power rather than a generator. Seattle uses this system. But may not be suitable in rural areas.

A cost comparison of these systems are:

● Passive smoke venting – About $2,500 with smoke detector activation

● Active air changing – About $5,000 - $9,000, plus fire alarm connection

● Active stair pressurization – Systems start at $50,000, not including engineering and method of backup power.

Occupant Evacuation Elevators and Fire Service Elevators: Code Requirements for Mid-Rise Buildings

Fire service and occupant-evacuation elevator features, standby power, protected lobbies, water-resistant hoistway components, are mandatory under the IBC only in buildings with occupied floors more than 120 feet above grade, and the broader high-rise elevator provisions apply only above 75 feet, both thresholds well above anything in the four-to-six-story range discussed here. An elevator in a building that if 5 stories or more will be required to be an accessible means of egress elevator, for occupants on upper floors who cannot use the stairs. Providing that means high-rise-grade protection in a low-rise building: standby power sized to the elevator load, a protected and communication-equipped lobby, and ongoing Phase I and Phase II testing. It's among the highest-cost measures relative to the size of a small building, and its value concentrates almost entirely on the accessibility side of the ledger, since able-bodied occupants in a small building can typically clear the stair faster than an elevator recall-and-Phase-II sequence would get them out anyway. Fire service tactical guidance reinforces this framing from the operations side: in buildings of four or five stories, fire service literature generally advises against using elevators for the initial attack crew at all, reserving them instead for moving equipment once conditions are confirmed safe, a materially different role than the one elevators play in a genuine high-rise. Cost can be lessened by not providing a generator, providing reliable municipal power instead, but not allowed in elevator codes. Being stuck in an elevator were smoke can reach is a bad condition to allow.

Fire Apparatus Access and Aerial Truck Requirements: Site Planning for Building and Fire Officials

Every protection measure inside the building assumes the fire department can actually reach it, and that assumption depends on decisions made at the site plan stage, often well before anyone is thinking about stair count.

The International Fire Code's Appendix D requires an aerial fire apparatus access road, not just a standard fire lane, wherever a building's highest roof surface sits more than 30 feet above grade, which covers every building in the four-to-six-story range. That access road has to be at least 26 feet wide, positioned between 15 and 30 feet from the building in most jurisdictions, running parallel to one full side of the building, with a minimum vertical clearance of 13 feet 6 inches, many departments prefer 14 feet in snow-prone regions, short vegetation along the sidewalk, and no overhead utility or power lines crossing the road or the space between the road and the building.

Site conditions that have nothing to do with the building itself, mature street trees, existing overhead utility lines, permitted on-street parking, can quietly compromise a fire department's ability to use an aerial device at all, regardless of how the building itself is protected. A code official evaluating a site plan gains real information by asking where the aerial apparatus road actually goes, not just whether one exists on paper, and a design team benefits from confirming utility and tree locations against this requirement early, since relocating a mature street tree or an overhead line after design is a far more expensive conversation than accounting for it up front. Some jurisdictions, under the same IFC appendix, will modify the standard setback for residential buildings under five stories where additional fire protection measures are provided, a mechanism worth understanding if a lot's dimensions make the standard range difficult to achieve.

Rear Yard Access and Fire Department Rescue for Non-Street-Facing Apartment Units

Aerial apparatus access addresses the street-facing side of a building. The units that don't face the street present a separate problem, and the solution depends heavily on whether the lot has a usable rear yard.

Where a rear yard exists, ground ladder access from that yard is often sufficient for a building in this height range: a portable ground ladder reaches a fourth or fifth floor window without requiring the vehicle access an aerial device needs, provided the yard is wide enough and clear enough of obstructions, fences, sheds, mature landscaping, to actually position a ladder. An exterior stair or a rear-facing egress balcony, discussed above, can also terminate in a rear yard, giving both occupants and firefighters a second usable path independent of the street frontage entirely.

Where no rear yard exists, a common condition on narrow, zero-lot-line urban infill sites or buildings built to a rear alley with minimal setback, the options narrow considerably. Ground ladder positioning may not be physically possible if there's no clear ground space to place it. An alley, where one exists, can sometimes substitute for a rear yard if it's wide enough for apparatus or ladder positioning, but alley width and clearance vary enormously by jurisdiction and are often controlled by an entity other than the building's owner. In this condition, the interior protection measures in this chapter, detection, notification, refuge, and the stairway itself, carry proportionally more of the life-safety burden, because the building genuinely has fewer exterior rescue options to fall back on. Site conditions, not the building's stair count, may be the binding constraint on what's achievable here, and it's worth evaluating before assuming any particular protection package will translate identically from one lot to the next.

Occupied Roof Deck Fire Code Requirements: Egress and Firefighter Access

An amenity deck, rooftop lounge, or shared outdoor space on the roof of a small apartment building introduces considerations distinct from anything else in this chapter, because current code treats an occupied roof as functionally equivalent to a story of the building for means-of-egress purposes, whether or not it technically counts as one for height and area calculations.

That equivalence carries real consequences. An occupied roof needs the same number of exits, based on the same occupant-load calculation, as any other floor, and current code requires free egress from an occupied roof back into the building, meaning the access door cannot simply be locked or keyed for fire-department-only use the way an unoccupied roof's access commonly is. Any wall, screen, or trellis structure enclosing part of the occupied roof is capped at 48 inches in height under the IBC specifically because taller enclosures create two hazards at once: they can trap smoke and heat at head height in exactly the space occupants are trying to move through, and they interfere with the sightlines and physical access firefighters need for rooftop ventilation operations, which remains one of the more common tactical uses of a roof during a fire regardless of whether anyone can be up there.

Rooftop mechanical equipment and, increasingly, rooftop solar arrays add a further layer: fire code requires clear pathways of a minimum width across a photovoltaic roof array specifically so responders can move across and ventilate the roof without an unbroken field of panels blocking them, a requirement that has to be coordinated with amenity space layout rather than treated as an afterthought once the deck design is finished.

Finally, if the only amenity space in the building, a pool, a lounge, a shared roof deck, exists exclusively on the roof, that can trigger an accessible-route requirement that a building otherwise exempt from providing an elevator would not have needed to meet, an interaction worth flagging early in design rather than discovering during plan review.

Occupied roofs create an egress hazard with a large occupant load at the highest floor in the building. Meaning that potentially there are a lot of people who may be impaired and not wanting to leave. A situation that could require a lot of rescues and be a large casualty event. A small deck with a steel trellis that is at least 70% open to the sky (interpretation of NFPA 13) is a possibility in some conditions.

Comparing the Measures

Bike Rooms and Smoke Vestibules: How They Protect People

There are two other types of spaces that can provide protection to buildings. These are not just for single stair buildings, but all buildings. The core reason they are good spaces to have in a building is based on the toxicity of smoke in battery and furnishing fires, two of the leading causes of fires today.

The first space addresses the newest concern for building fires, micro-mobility devices, e-bikes, e-scooters, and all things battery powered. Bike rooms are already required in most urban zoning codes, to provide a place on the ground floor for people to park bikes and other mobility devices. The storage occupancy type can require these rooms to be fire-rated, but not always.

PABs should have these rooms on the ground floor, not just for convenience, but also to keep the potential for battery fires out of the rest of the building. These rooms need to be at least one-hour rated, with a 2-hour rating providing additional protection for these types of fires. These fires are difficult to put out and emit toxic smoke, therefore should not have any doors that open into the stair.

The second space is a smoke vestibule in front of the stair door. A smoke vestibule can act as a second layer to prevent smoke from entering a stair. Some codes require them in lieu of pressurizing a stair, though they also need a fan to help keep smoke out. The fan may not be needed, relying on a fire rated door between the unit door and the stair door to help prevent smoke into the stair, as an extension of the stair protection.

PABs are designed to maximize apartment area and providing a vestibule that has to be at least 7' long, to accommodate doors in a series requirements, may be too much for most designs. Unit doors cannot open into this vestibule or the stair, meaning that the minimum 28 square foot vestibule impacts unit design. Combining areas of refuge in stairs with smoke vestibules would take up over 10% of the available floor area per floor.

Practical Takeaway: Selecting Fire Protection Measures for Building Design and Code Review

None of the measures above are presented as a required package, and stacking all of them onto a single building is neither necessary nor, in most cases, a good use of a limited construction budget. The measures that matter most for a given project depend on a small number of site-specific and climate-specific questions. How tall is the building, and does its height make stack effect or elevator accessibility the more pressing concern? What's the local climate, and does it favor a mechanical solution like pressurization or a passive one like venting and exterior stairs? What does the lot actually offer, a rear yard, alley access, generous setbacks, or none of the above, and how much of the life-safety burden does that leave for the building's interior systems to carry? Who is expected to occupy the building, and does that population's mix of ages and mobility levels make an area of refuge or an accessible elevator path more or less of a priority than it would be in a different building?

A code official, architect, or developer who works through these questions before reaching for a specific protection measure will generally land on a smaller, more targeted set of choices than a checklist approach would produce, and a smaller, well-matched set of protections is very often the more defensible one, both on cost grounds and on the engineering logic each measure is actually built on.

Zoning Regulations and Elevator Codes: Policy Barriers to Missing Middle Housing Development

What other actions need to happen

Well-protected small single-stair apartment building meets or exceeds the life safety performance of a large two-stair building. If that argument holds, and the data on equivalence says it does, then something other than fire safety are reasons these buildings aren't going up on more lots, in more American cities. Two things, specifically. Neither one is a building official's decision, and neither one will be solved by life safety protection measures. This chapter names them directly.

Elevator Cost Comparison: United States Versus Europe Elevator Codes and Construction Costs

Start with a number that has nothing to do with sprinklers or stair count. Installing an elevator in a new mid-rise building costs roughly three to four times as much in the United States and Canada as it does in Western Europe or East Asia. Research from the Center for Building in North America, the same research community behind the Pew Charitable Trusts' single-stairway safety study, puts a typical U.S. or Canadian installation at $150,000 or more, against roughly $50,000 in several high-income peer countries. One frequently cited comparison makes the gap concrete rather than abstract: a Schindler MRL electric traction elevator installed in Vaud, Switzerland in 2020 cost $35,348. A comparable Kone MRL electric traction model installed in New York City cost $157,856, more than four times as much for functionally similar equipment.

That gap isn't explained by labor costs alone, construction complexity, or anything resembling a genuine safety improvement. Three specific, identifiable causes account for nearly all of it. First, cabin size: U.S. and Canadian code requires an elevator car large enough to carry a fully reclined seven-foot stretcher, producing a car roughly twice the size of the wheelchair-and-stretcher-accommodating cars standard in Western Europe. The irony is worth stating plainly: the American car, more square than the narrow, deep European car built for the same purpose, frequently doesn't reliably fit a fully reclined stretcher either, despite costing far more and consuming far more floor area to install. Second, technical standards: the United States and Canada are among the only developed markets in the world that haven't harmonized with the EN 81 standard used across the European Union, walling off American developers from a global parts and component market that keeps European equipment cheap and widely serviceable. Third, labor: elevator installation and maintenance in North America runs through a licensure and training structure that restricts the supply of qualified workers far more tightly than the government-sponsored technical education pipelines common in the European countries this comparison is drawn against.

How a Lack of Elevators Impacts People

The downstream effect on building design is direct and well documented. In Western Europe, a small point access block of ten to twelve units routinely includes its own small elevator, because that elevator is affordable enough to fit the project's budget at that scale. In the United States, the same building either skips the elevator entirely and stops at three stories, the practical ceiling for a walk-up, or shares a single expensive elevator across fifty to a hundred units to spread the cost, a design choice that increases how heavily that elevator gets used and, with it, how often it breaks down.

This is a minor fire-safety trade-off, but a large accessibility impact. It's a regulatory and market-structure problem that happens to land directly on top of this exact building type. Trying to build more housing for more people must include the means for the physically impaired to have access to more housing as well.

How Elevators Need to Meet Fire Safety Needs

Elevators have operational as well as fire safety elements that impact life safety. Elevators for the 5th story and above can be used by firefighters to reach building floors, but they are also shafts where smoke can migrate between floors.

Where elevators are provided in apartment buildings, elevators that serve the 5th floor and above are required to meet the provisions as an accessible means of egress elevator. This includes a communication device adjacent to the elevator, specific controls that allows firefighters to use the elevator to assist people to the ground floor, and most costly, standby power. The building’s power is shut off during a fire, so a generator or other means needs to be provided to allow the elevator to operate.

These elevators can assist firefighters in other ways, sometimes used by firefighters reach upper floors for clean-up operations, plus they can be an efficient means to get extra SCBA tanks and other equipment to the upper floors.

Elevators do have a key weakness when it comes to smoke migration, the doors do not seal tightly. They allow smoke, especially when it is pressurized by a fire, to enter the elevator shaft and migrate to other floors.

To prevent this from impacting egress on other floors, elevator lobbies are required in high-rises, with smoke draft curtains or doors provided to cover and seal elevator shaft doors in low and mid-rise buildings. For a six-story apartment building, these run about $7,000 per elevator door or a little over $1,500 per unit on that floor. Not a small impact.

Zoning Height Limits and the Fair Housing Act: Why U.S. Zoning Caps Buildings at Three Stories

The second obstacle sits in zoning and accessibility law rather than the elevator code, and it compounds the first one rather than operating independently of it.

A large share of U.S. residential land is zoned in ways that cap buildings at two or three stories regardless of what the fire code would otherwise permit, through height limits commonly in the 25-to-35-foot range, minimum lot sizes, and setback requirements that together lock a neighborhood into a low-rise, low-density form by design. Even where a city has done the harder work of adopting single-stair provisions, as New York and Seattle have, an independent zoning ceiling can still cap most buildings well below the five-or-six-story range where the safety case has the most room to operate.

The three-story number isn't arbitrary, and understanding why sharpens the case for changing it. The Fair Housing Act requires every unit in a building with an elevator to be built as an accessible, adaptable unit. A building without an elevator only needs its ground-floor units to meet that standard. Layer the IBC's own single-stair threshold on top, most versions of the code cap a single-stair floor at four units before requiring a second stair and a rated corridor sized to the building's diagonal, and a developer working the numbers lands on the same answer from two different directions: stop at three stories, four units per floor, no elevator, and avoid both the elevator's direct cost and the accessibility retrofit cost that comes bundled with it.

That's not a builder cutting corners. It's a rational response to a code structure that makes going one story taller disproportionately expensive compared to the two stories before it.

The building types this produces are recognizable by name in most American cities: the three-story garden apartment walk-up, the West Coast dingbat, the small multiplex that stops just short of needing an elevator. Reform efforts aimed at this pattern, loosely grouped under the term "missing middle housing," have shown the ceiling can move. Minneapolis eliminated single-family-only zoning citywide in 2018. Oregon's House Bill 2001, passed in 2019, did the same at the state level for its larger cities. California's SB9, effective in 2021, opened most single-family lots in the state to duplexes.

Zoning Density: Why the U.S. Zoning Prefers Houses to Housing

Since World War II ended in 1945 and the development of Levittown on Long island starting in 1947, the U.S. has focused on The American Dream, owning a house. The GI Bill, FHA loans, and 30-year fixed mortgages cemented home ownership as a path to personal stability, adulthood, and middle-class wealth building. Policies cemented home ownership as the vehicle for personal freedom and investment in the community.

These policies and political pronouncements on the American Dream have resulted in suburban sprawl as populations grew. These policies now extend sprawl based on affordability on cheaper land, which has lead to 2-3 more deaths per capita occurring in houses without proper alarms and sprinkler systems.

These policies and personal freedom mindsets have lead to NIMBYism as policy makers attempt to change zoning regulations to allow more dense housing options. It is a fight at every block, but a fight that needs to occur and home prices go up and populations continue to grow.

None of these changes touched a fire code. They touched the zoning and land-use rules sitting in front of it, and they show that a ceiling built by policy can be raised by policy. More efforts across the country are needed.

Elevator Code Reform and Zoning Policy Change for City Planners and Legislators

Fixing either barrier is a different project than the one the fire life safety concerns bring up, and it needs a different audience.

State elevator boards and the committees that maintain the ASME A17.1 standard can open a harmonization path for cabin sizes and technical provisions suited to low-rise buildings, rather than requiring every installation to meet a specification built around the tallest, most complex buildings in the country. A few states have already begun exactly this kind of variance process; more doing the same would widen the market for smaller, more affordable equipment faster than any single project can on its own.

State legislatures and licensing bodies can expand the technical training pipeline for elevator installation and maintenance, following the model of the government-sponsored programs that keep the labor market for this work larger, and the price of that labor lower, throughout Western Europe.

City councils and zoning boards can raise by-right height limits to match the building safety case actually covers, particularly in cities that have already done the harder work of permitting single-stair construction. A fire code reform that stops delivering more housing at the zoning line isn't finished, it's half done.

Minneapolis, Oregon, and California have already shown that a zoning ceiling set by policy can be moved by policy; the next round of reform doesn't need to invent that playbook; it needs to run it again, aimed specifically at the height where an elevator, a single stair, and real housing supply all start to pencil out together.

And architects, developers, and others have a role that doesn't require waiting on any of the above. Document what an elevator actually costs on your own next project, and where. Bring that number to your own city council or zoning board, the same way this book has asked you to bring the fire science to your own code hearing.

A stair count argument backed by data changed the conversation in New York and Seattle. A cost argument backed by data can do the same for the zoning line sitting above it.

Practical Takeaway: Elevator Cost and Zoning Data for City Planners and Policymakers

Two figures travel well into a room that has never thought about elevators or zoning as fire-safety adjacent issues at all.

First, the elevator cost gap: three to four times more expensive in the U.S. and Canada than in Western Europe or East Asia, driven by cabin size, technical standards, and labor supply, not by any genuine safety advantage.

Second, the three-story ceiling: a height cap that traces directly to the Fair Housing Act's accessibility trigger and the IBC's single-stair unit-count threshold, both of which reward stopping one story short of an elevator rather than building the story that would actually make one affordable to include.

Neither number belongs to the fire marshal. Both belong to the state elevator board, the zoning board, and the legislature, which means both are exactly as fixable as the fire code equivalence case this book has already made, provided the right audience hears them.

Conclusion: A Call to Action: Building More Missing Middle Housing Through Code and Zoning Reform

A Call to Build

The discussion in this book points toward one conclusion: small single-egress-stair apartment buildings meet, and in key respects exceed, the safety standard two-stair buildings are held to. The data holds up. The physics holds up. The building stock already standing in New York, Seattle, and cities across Europe holds up. What's left isn't a safety question. It's a decision.

Architects, this is the case to bring your next client. Developers, this is the lot you passed on because assembling five parcels never penciled out; a single lot might. Building and fire officials, this is the equivalence argument to weigh on its evidence, not on a stair count written into code before sprinklers, modern detection, and compartmentation existed to do the job redundancy was meant to do. Policy researchers and legislators, this is the code pathway other jurisdictions have already proven out, waiting for the next one to follow.

None of this argues for lowering the bar on safety. It argues for meeting that bar through means the data supports, on lots the housing market actually has available, at a scale that lets more builders, not just the largest ones, bring more homes to more people. Every jurisdiction that makes this shift adds housing stock that would otherwise never get built, on the same terms of safety as larger apartment buildings.

The people who need this housing are already living in your community, waiting for it to exist. Build them somewhere safe to live, and build enough of it to matter.

My Recommended Path Forward: Logical Code Changes to Build More Housing

The 2027 International Building Code (IBC) Section 1006.3.4(1) will allow 4 story R-2 apartment buildings, limited to 4,000 s.f. and 4 dwelling units per floor. Additional protection measures include smoke detectors connected to the building-wide fire alarm system and a noted restriction on electrical outlets in the stair, where they should already be banned.

Additional protection measures that I would recommend to include to extend the allowances of IBC Section 1006.3.4(1) would be enlarged floor landing, 66” minimum, on the stair to accommodate those who cannot physically go down the stair, escape windows in street-facing stair, if the stair is provided with a street-facing side, and provide a supervised sprinkler system per 2024 IBC 903.4.1, 903.4.2, and NFPA 72.

Because this may be a leap of faith for many to accept, until time shows the safety these small buildings contain versus code-compliant large apartment buildings, two further protection measures can be implemented, a fire-rated bike room and small exterior balconies in the rear yard setback. These items address the concern over battery fires in e-bikes and scooters, and provides a place for people to get out of the smoke if the corridor becomes too smoky. Though the bike room may mean the loss of a dwelling unit, it does help to remove a serious fire threat from apartments.

That’s it, no more protection measures needed to provide equivalence to what is allowed in large two-stair buildings, and that is the standard the building and fire codes are based. As much as we would like, we cannot prevent all fires and all fire injuries. These measures, to me, provide people the protections they need to escape a fire, and firefighters the means to conduct their life-saving operations without too much impairment from occupants continuing to need to be rescued or egressing late.

APPENDIX 1

Opposition Point: The case against Point Access Blocks

An appendix on based on International Association of Fire Fighters points against single exit stair buildings, compiled in support of the Point Access Block life-safety argument

Executive Summary

This appendix provides the primary opposition to Point Access Blocks, it doesn't come from NIMBY zoning boards or risk-averse insurers. It comes from the people who run into burning buildings for a living. The International Association of Fire Fighters (IAFF), joined by the International Association of Fire Chiefs' Metropolitan Fire Chiefs Association, has issued formal position statements opposing single-exit residential buildings in the United States and Canada.

I do not want to dismiss those arguments.

Taking the IAFF's case seriously, on its own terms, comes down to three arguments that carry the most weight. Relying on data on modern buildings and where that data runs out addresses the IAFF's specific objection that proponents of single-stair reform have not produced adequate egress research of their own, because that criticism is fair and I do not pretend otherwise.

Three Arguments Against Point Access Blocks

Argument One: The Single Point of Failure

The IAFF's position statement puts it plainly: a single-stairwell building provides only one path of egress, and if that route is blocked by fire, smoke, explosion, or structural failure, occupants and fire fighters face catastrophic consequences. The statement grounds this in the Triangle Shirtwaist Factory fire of 1911, where locked exit doors and a single collapsing fire escape trapped 146 garment workers.

Why the concern exists

A blocked or compromised sole stairway is the worst-case outcome any egress system is designed to prevent. We already walked through why Dykeman Street, Grenfell Tower, and Twin Parks Northwest turned fatal, and in each case the single or shared path to the outside is exactly where the deaths occurred. These events will overshadow any event-tree probability. The instinct to demand a second way out is earned, and there is no use in trying to argue it away.

What the data on new buildings shows

Three things distinguish a modern Point Access Block from Triangle Shirtwaist or Dykeman Street:

1) Automatic sprinkler systems and fire alarms with smoke detection,

2) the stairway is a rated, enclosed, sprinklered enclosure rather than an open shaft, and

3) every apartment door swings into a corridor rather than opening directly into it.

New York City and Seattle's decades-long track record with permitted single-stair construction, has not produced a documented pattern of stairway-compromise fatalities in buildings built to those standards.

What additional data is needed

The event-tree modeling this book relies on is a risk model, not a record of lived outcomes across a large, aging building stock. What's missing is longitudinal, incident-level data tracking stairway-compromise events specifically in code-compliant single-stair buildings as that stock ages past 20 and 30 years, the point at which deferred maintenance and system degradation are most likely to show up.

That data does not yet exist in usable form, for two reasons: New York and Seattle have not tracked their incident reports thoroughly enough to make data usable, and nearly all other buildings are too new.

There are many international buildings that would provide the historical data, but differences in construction standards, sprinklers, and alarms make that data unusable as a form of comparison.

Counter-argument

Looking at the scenarios where fire, smoke, explosion, or structural failure blocks the exit path to the stair

· Fire breach of an apartment will have made the corridor so filled with smoke that egress in it is untenable, unless you know exactly where the stair door is and can hold your breath to get there.

· Smoke-filling studies show that there is a time difference of a few minutes where the corridor becomes untenable for egress, longer corridor stays tenable for longer. That difference is countered by the time someone has to stay in the smoke. In a PAB, you can hold your breath to the stair. In a longer corridor, any smoke will slow you down, with burning eyes and coughing. You cannot hold your breath the whole way. The Cleveland Clinic states that two breaths of smoke is enough to incapacitate someone.

· Explosion and structural collapse will likely affect the entire building of a PAB. In a PAB, these events also can only affect 10% of the possible occupants of a large two-stair building. In a two-stair building, those unaffected can use the other stair, but the number affected people can be significantly more.

Argument Two: Fire Fighters and Occupants in the Same Stairwell

Why the concern exists

In a large apartment building, there would likely be 4x-5x the number of people using that stair (20 occupants/floor vs. 200 occupants/floor, 100 per stair). The argument seems to hold true after about 10 minutes after the fire has started. While 10 minute evacuation times are not uncommon in large buildings, in small buildings with less people and faster egress speed due to less congestion (think freeway flow), there are few people left in the building.

What the data on new buildings shows

The Minnesota study modeled this scenario directly: occupants egressing down the single stair at the same moment fire fighters begin advancing up it, the most conservative version of the conflict, with no coordination between the two groups.

Even under that condition, full building discharge for the single-exit prototypes took 5 to 7.5 minutes, worse than the 2.5-to-5-minute discharge without fire fighters present. Given firefighter response times to arrive at the fire, deploy, and start up the stair, 5-7 minutes after alarm, most everyone is out. Those left are probably not self-evacuating.

This is still faster than the two-exit building's modeled 16-minute full discharge.

The geometry that makes single-stair buildings fast to clear in the first place, few units per floor and a short corridor, is the same geometry that limits how much the cross-flow conflict exists.

What additional data is needed

That result is a simulation, not a measurement. No dataset yet exists tracking actual fire fighter operational tempo, injury rates, or delay in real single-stair apartment fires with residents still egressing, because the modern stock of these buildings has not generated enough working structure fires with fire fighters present during active evacuation to build one.

The right source for that data going forward is standardized post-incident reporting that specifically flags egress-and-attack path conflict as a coded variable, tied to building type. That level of detail does not exist yet in a usable historical dataset.

Whether this is due to a lack of incidents even occurring (a good thing), or lack of data collection (fixable), is still to be determined.

Counter-argument

Speed of egress means less people in the stair by the time the firefighters arrive to deploy up them. This is different in two-stair buildings where people are still largely egressing down crowded stairs when firefighters deploy up them, directing them to move to the other stair as they move upward. The second stair is not empty when they arrive, a similar effort, if not worse, going up a more crowded stair before directing them to the other stair.

Argument Three: Reliance on Building Systems That Must Be Maintained

The IAFF's position statement raises a systems-reliability objection that deserves more weight than either side usually gives it: proponents of single-stair reform lean heavily on sprinklers, alarms, and compartmentation performing exactly as designed, over the entire life of the building, and the IAFF is explicit that it does not trust that assumption to hold.

The statement cites an independent risk assessment commissioned by British Columbia from Jensen Hughes, which scored the probability and severity of failure across egress-related building systems. Fire-rated construction integrity was rated a probability of failure with Catastrophic potential severity, a Risk Score of 16, in the assessment's own unacceptable range. Inspection and maintenance practices scored a probability of failure with Critical severity, a Risk Score of 12, also unacceptable.

The report's own language is worth repeating: inspection and maintenance is the most critical component in ensuring these systems perform as designed, and the IAFF's statement notes that single-stair proponents offer no advocacy for improved inspection and enforcement to go along with the reduced egress redundancy.

Why the concern exists

The data supports the IAFF's worry more than it undercuts it. It is well established that observed sprinkler reliability sits around 88 percent, and only reaches roughly 96 percent where NFPA 25 and NFPA 72 inspection, testing, and maintenance programs are actually enforced. That eight-point gap is real. It is, by the Minnesota study's own risk modeling, responsible for the large majority of the comparative fire risk across every building geometry tested.

What is left unsaid, is that two-stair buildings have the same issues on maintenance. With many more occupants per floor, the failure of the sprinkler, alarm, or rating integrity is multiplied in its impact.

A single-stair building has removed the one piece of redundancy, a second physical path, that does not depend on anyone showing up to service it. Everything the PAB equivalency argument substitutes in its place, sprinklers, detection, self-closing doors, does depend on that. The IAFF is not wrong to name that trade-off directly.

What the data on new buildings shows

Where jurisdictions enforce ITM programs aggressively, sprinkler reliability data supports the equivalency claim; where they don't, it doesn't. New York City and Seattle's decades of operating experience with single-stair buildings both come from cities with active, resourced fire code enforcement, which is not incidental to why those buildings haven't produced a documented pattern of failures.

That is a point in favor of the equivalency argument, but it is a conditional one: it holds where enforcement holds, and it says nothing about what happens in a jurisdiction that adopts single-stair permissions without the enforcement capacity to back them.

What additional data is needed

Two things are missing. First, jurisdiction-by-jurisdiction ITM compliance rate data specific to small, single-stair apartment buildings, as distinct from the broader sprinklered building stock NFPA reliability figures are drawn from; small buildings with thinner ownership and management structures may inspect and maintain systems differently than large professionally managed properties, and nobody has published a study isolating that variable. Second, a longitudinal failure-rate study following single-stair buildings specifically past the 20-year and 30-year maintenance-deferral risk points the Jensen Hughes assessment flags. Neither dataset currently exists.

The need for the data exists. The equivalency risk assessment is whether the data will show a distinct difference in failures due to lack of maintenance in the two building types.

The question comes down to whether a fire-rated construction integrity failure would exist in the stair containment or in the corridor containment. The likelihood is in the corridor rating, which has a higher impact, and higher likelihood, in a building with more occupants and more corridor wall.

Same can be said on maintenance concerns, the possibility and impact of failure of a system is much higher in larger buildings.

Maintenance of Life Safety Systems and the Case for Simplicity

The IAFF's maintenance objection points at a real vulnerability in any protection strategy that depends on active systems. But it also points, unintentionally, at the strongest argument for why a Point Access Block's approach to that vulnerability is more defensible than a large two-stair building's, not less.

Every additional life-safety system a building carries is one more component someone has to inspect, test, and repair correctly, on schedule, for the life of the building, and one more component that can be skipped when a maintenance budget gets tight. A large two-stair apartment building built to the code minimum typically carries a second stairwell enclosure, a stairwell pressurization system in taller configurations, an accessible-egress elevator with standby power and firefighter recall controls, elevator lobby smoke curtains or pressurized lobbies, and the same sprinkler, alarm, and compartmentation systems a PAB carries. Every one of those additional systems is a separate maintenance obligation, a separate inspection line item, and a separate point where deferred maintenance or an undertrained technician can quietly turn a paper compliance record into a real-world failure nobody discovers until a fire finds it.

This is Occam's razor applied to fire protection: the system most likely to still be working correctly in year twenty is the one with the fewest moving parts someone has to remember to service. A PAB's protection strategy deliberately concentrates its redundancy budget into a small number of systems, sprinklers, detection, and self-closing rated doors, that building owners and fire marshals already inspect as a matter of routine code compliance, rather than distributing that budget across additional mechanical systems, standby power infrastructure, and pressurization equipment that require their own specialized maintenance contracts and are easier to let slide. Fewer systems to maintain is not a shortcut. It is a maintenance strategy, and a defensible one, precisely because the data in the previous section shows that maintenance, not design, is where the real risk lives.

This does not answer the IAFF's objection outright. It reframes the objection: the question is not single-stair versus two-stair, it's which set of systems is more likely to actually be maintained twenty years from now, by the kind of ownership that a small, single-lot apartment building attracts. That is an empirical question, and it is one more reason the additional ITM compliance data called for above matters as much as it does.

What NFPA, NFIRS/NERIS, and FBI Data Show About Modern Apartment Buildings

The national data on apartment fires is worth stating plainly, both because it supports parts of this book's argument and because it exposes exactly the gap the IAFF is pointing at.

NFPA: the trend is real, but the resolution is too coarse

NFPA's 2024 fire experience survey recorded roughly 76,000 apartment or multifamily housing structure fires, about 5 percent of all reported fires that year, resulting in 340 civilian deaths, 9 percent of the national total, 2,290 civilian injuries, 19 percent of the total, and roughly $2.0 billion in direct property damage. Apartment fire deaths have declined substantially since the 1980s, when they averaged roughly 840 a year, a trend most fire protection engineers credit to the spread of required sprinkler systems, smoke alarms, and compartmentation, the same systems this book's equivalency case leans on.

What that national trend line cannot do is answer the specific question this chapter is about: whether single-stair apartment buildings perform differently than two-stair buildings once built. NFPA's structure fire data is not broken out by number of means of egress, and no national dataset currently ties fire outcomes to that specific design variable at the building-stock level. That absence is not a flaw in NFPA's data collection. It's a reflection of the fact that nobody has built the linkage yet.

NFIRS to NERIS: the data infrastructure this book needs is only months old

This is the most important data-availability fact in this chapter, and it belongs in the manuscript explicitly. The National Fire Incident Reporting System, the federal incident-reporting backbone fire departments have used since 1976, was formally decommissioned as of February 2026, replaced by the newly launched National Emergency Response Information System, or NERIS. NERIS began onboarding departments in November 2024, with reporting becoming mandatory and exclusive as of January 2026. It is a genuinely more capable system, cloud-based, real-time, and built to support the kind of granular, cross-referenced incident analysis, including newer fields like lithium-ion battery involvement, that NFIRS's 1970s-era architecture could never support well.

The practical consequence for this book's argument is that the tool capable of producing the exact dataset this chapter calls for, incident-level records tied to building egress configuration, ITM compliance history, and fire fighter operational outcomes, has existed in national deployment for barely a year at the time of this writing. There is no multi-year NERIS trend line yet, because there hasn't been time to generate one. This is not a reason to abandon the equivalency argument. It is a reason to say directly, in this book, that the single best answer to the IAFF's own demand for egress research is now technically possible in a way it wasn't five years ago, and that fire service organizations and single-stair advocates have a shared interest in specifying exactly what NERIS should track on this question before another decade of buildings gets built without it.

FBI arson data: enforcement and occupancy status matter more than stair count

FBI Uniform Crime Reporting arson data has historically broken out structure fires by property type, with residential structures other than single-family homes, the closest available category to apartment buildings, accounting for roughly 7 to 8 percent of all reported arson offenses in recent reporting years, at an average dollar loss in the high five figures per incident.

Two details in that data are more relevant to this chapter's argument than the raw share: a disproportionate share of arsons in that category occur in structures reported as not in use, and reported arson totals nationally have trended downward over the past decade even as total fire counts have not. Both details point toward the same conclusion the IAFF's own maintenance objection points toward: enforcement, occupancy oversight, and building management quality predict fire outcomes more directly than the number of stairwells does.

That's a data point that cuts both ways, since it also means a single-stair building and two-stair building in a poorly managed, poorly inspected portfolio carries exactly the compounded risk the IAFF is warning about. The impact in a larger two-stair building is higher, with more people able to be impacted.

Where This Leaves the Argument

None of the three arguments against Point Access Blocks examined in this chapter are bad-faith or ignorant of fire science. Each is grounded in a real fire, a real physical vulnerability, and a real professional's direct experience with what happens when a building's protection systems don't hold. The honest response that the IAFF’s concerns need further research.

The question becomes, what is the real difference in impact on occupant and firefighter safety in single-stair vs. two-stair buildings?

- A single point of failure has more impact in larger buildings because it is the smoke in the corridor that has the most impact in preventing people from being able to reach a stair.

- Contra-flow is worse in larger buildings with more occupants as clearing a stair of more people slows access to the fire floor more than with less people.

- System failures due to lack of testing and maintenance is compounded in larger buildings with more elements that can fail, disabling the system for more people.

We respect the fire service objections and hesitancy; this is a real concern.

What is needed is a joint research agenda: NERIS-coded tracking of egress configuration against incident outcomes, jurisdiction-level ITM compliance data specific to small multifamily buildings, and post-incident reporting that captures fire fighter and occupant path conflict as a variable rather than an anecdote.

Two things are needed to ensure the point access blocks remain as safe for occupants and firefighters as the perception of two-stair building remains, training and education.

Training for fire fighters in how to best operate in these buildings. There are examples internationally, but the training programs and sessions need to be implemented to ensure firefighters know best procedures for their safety.

Education for the public so they know what to do in case of a fire. After Twin Parks North West there was consideration of educating occupants on a defend-in-place strategy. A similar debate that has occurred in England since the Grenfell Tower fire. For point access blocks signage and education needs to be implemented to ensure occupants know what to do when the fire alarm sounds. Education is key to faster reactions, therefore faster times to safety.

Once again, speed is the key factor here, speed of firefighter operations to control the fire and rescue those that need it, and speed of occupant reaction and egress.

APPENDIX 2

Corridors: Smoke-filling, Door Gaskets, and Pressure Differentials

A data appendix on the corridor, door gaskets, pressures in a fire, compiled in support of the Point Access Block life-safety argument

Executive Summary

This appendix asks three questions:

· what actually happens to smoke in a corridor,

· whether a smoke gasket protects the occupant who stays behind a closed door,

· what tight modern construction does to the pressure differentials that push smoke where it goes.

Two field-grade sources answer them: 19 live-fire tests run by the Dutch Fire Service Academy in an occupied residential building, and the Minnesota DLI/WJE-Crux single-exit stairway risk analysis.

None of the findings are comfortable for a pure PAB advocacy case. Corridor length does not meaningfully delay when smoke arrives; a ceiling-level smoke front crossed a 19-metre (62 feet) corridor in 10 seconds once a fire-room door was opened, and the Minnesota report separately concluded a short PAB corridor fills fast enough that a second stairway shaft would buy little. Smoke gaskets built to the S200 standard performed almost identically to an ordinary closed door once that door was opened for just 30 seconds, and the same airtight construction that gaskets depend on drove fire-room pressure up to 1,010 Pascal (4 inches of water column), roughly forty times higher than the pressure current smoke-seal certification testing actually covers. A tighter exterior envelope does not reduce smoke migration into the building; it relocates it, forcing pressure through interior partitions instead of outward through the skin.

This appendix’s other finding cuts against the two-stair building instead. Occupant familiarity with a stairway's location, not its rated capacity, determines whether it gets used. Three independent studies, a building survey, a controlled virtual-reality experiment, and an agent-based simulation, converge on the same conclusion: an emergency-only stair is recognized by a small fraction of the population that recognizes the stair used daily, and the resulting delay compounds as occupant load grows, potentially eroding much of the redundancy a second stair is credited with on paper.

This appendix closes with a concrete infographic, split by whether an occupant can self-evacuate or must defend in place, built directly on the finding that carries the most weight across every test and study reviewed here: the decision made at the door, not the hardware on it, determines the outcome.

Corridor Smoke Filling: Length Changes Less Than Assumed

The Dutch field tests were run in a fixed 19-metre by 1.8-metre corridor, and the report is explicit that corridor length was not the variable under study. Its own conclusion states plainly that smoke production at the source and the opening of the fire-room door were the decisive factors, and that corridor size was, at most, secondary. That's worth stating in this book directly, because it means the field data does not prove that a short PAB corridor outperforms a long two-stair corridor on smoke filling. It proves something more specific, and more useful.

Before the fire-room door was ever opened, smoke leaking through the gap under and around a closed door reached the corridor within 2 to 2.5 minutes of ignition, but never dropped visibility below 5 metres. That leak is slow and self-limiting, because it depends on gap size, not corridor length. Once the door was opened, at the 5-minute mark in the test protocol, the smoke reached the full 19-metre length of the corridor in 10 seconds, moving in both directions from the doorway as a ceiling-level gravity current. That is the number this book should use, and it should be used carefully: 10 seconds to traverse 19 metres is roughly 1.9 metres per second, fast enough that a longer corridor does not meaningfully delay the smoke's arrival at the far end. What a longer corridor does change is how long it takes the layer to descend from the ceiling to breathing height once it arrives, since that depends on the volume of air available to absorb the same mass of smoke. A short corridor has less volume, so the layer at head height collapses sooner near the source. A long corridor has more volume to work with, but also more distance for an occupant to cover before reaching a stair, once that layer starts descending everywhere at once.

The Minnesota TAG report reaches the same conclusion from the opposite direction, and states it as a limitation on the value of a second stairway rather than a virtue of a short one. In assessing whether scissor stairways would meaningfully improve the risk profile of the 4,000 sf single-exit prototype, the Consultants concluded that the benefit would be small, in part because the corridor serving that prototype "is so small that it will quickly fill up with smoke and obscure the access to either exit." That is a direct, citable statement that a short corridor's speed advantage and its smoke-filling risk are the same physical fact viewed from two directions: less volume means less exposure distance to cover, but it also means less capacity to buffer smoke before the whole corridor, including access to both exits in a two-exit design, is affected. This book should present the finding this way rather than as an unqualified point in the PAB's favor: the corridor's short length reduces total exposure time for occupants who move immediately, and it does not meaningfully slow smoke arrival at any point along its length.

Familiarity with the Stair Door: Speed and the Decision Itself

Neither field report treats occupant familiarity with the stair as a measured variable, but both touch it directly enough, and the wider egress literature is specific enough, that this book should not skip it. Familiarity affects two separate things that this chapter has otherwise treated as one: how fast an occupant who has already decided to evacuate can move, and which decision, evacuate or defend in place, an occupant makes at all.

Familiarity and movement speed

The Dutch report's own human-behavior section states the relevant finding directly: "when people try to escape, they will be inclined to choose a route they know, even if it is full of smoke." That is not a hypothesis; it is cited as an established behavioral pattern (Kuligowski, 2016), and it matters differently for the two building types this book compares. A single-stair Point Access Block removes the choice entirely. There is one stair, occupants use it to get their mail, and there is no wrong turn to make under stress because there is no alternative to weigh. A two-stair building does not get this benefit automatically, and may not get it at all, because the redundancy the code credits it with depends on occupants actually knowing where the second stair is and being willing to use it.

Song, Park, Bang, Agnew, and Charter's 2019 study in Fire Technology ("Spatial Familiarity and Exit Route Selection in Emergency Egress," Fire Technology, vol. 55, pp. 2269-2287) surveyed 69 occupants of a six-story library building on the location of stairways, restrooms, and elevators, scored against their actual positions. The study's central finding is that building familiarity and exit familiarity are not the same thing and should not be treated as interchangeable in fire engineering: an occupant can know a building well in general and still not know where its emergency-only exit is. On the specific question this book is built around, an occupant's location of a stairway used for daily, non-emergency circulation was correctly identified by 33 of the 69 respondents; the same occupants correctly located an emergency-only stairway only 8 times out of 69, a rate the authors describe as low as 20 percent of the regularly used stair. The study also found that once occupants have good general building familiarity, they orient toward a known destination by direction rather than by identifying the nearest available exit, which is a second, independent reason the closest stair is not necessarily the one an occupant under stress will choose.

Kinateder, Comunale, and Warren tested this directly in a controlled experiment rather than a survey, using an ambulatory virtual-reality museum ("Exit choice in an emergency evacuation scenario is influenced by exit familiarity and neighbor behavior"). Participants entered the virtual space through a "familiar" door, then were told to evacuate as they normally would when a fire alarm sounded, with a second, unfamiliar exit equally available. They were significantly more likely to leave through the familiar door than the unfamiliar one, confirming under controlled conditions what post-incident interviews have long described as "movement to the familiar." The study adds a variable this book has not yet accounted for: the behavior of other evacuees around them. The pull toward the familiar exit grew stronger when virtual neighbors also left by that door, and weakened when neighbors used the unfamiliar one, with the effect more pronounced with two neighbors present than with one. That is a direct, experimentally demonstrated social amplifier on top of individual unfamiliarity: in a crowded two-stair building, the bias toward the known stair is not just an individual habit, it is one that visibly reinforces itself as others are seen doing the same thing, which works against the second stair being used in proportion to its rated capacity precisely when that capacity is needed most.

NIST's evacuation research from the World Trade Center adds the decision-time cost directly: unfamiliarity with stairwell locations, including uncertainty about whether a given stairwell reached the ground floor at all, was cited by evacuees as a specific factor that delayed their decision to begin evacuating in the first place, before any movement time was even spent.

A 2025 agent-based simulation study in Sustainability (Wang, Shi, Che, and Xie, "The Dominant Role of Exit Familiarity over Crowd Interactions and Spatial Layout in Pedestrian Evacuation Efficiency") makes the strongest quantitative case available for treating familiarity as the controlling variable rather than one input among several. The model tested exit familiarity against crowd composition, imitation behavior, and storage layout, across three information conditions: occupants who know the exit's exact location, occupants who know only its general direction, and occupants with no exit information at all. Average evacuation time rose from roughly 300 time steps with full exit knowledge, to roughly 450 to 470 with partial knowledge, to roughly 9,500 to 9,600 with no exit information, a full order of magnitude increase between complete and absent exit familiarity, dwarfing every other variable the study tested. The authors found that the intensity of imitation among evacuees, essentially how strongly people copy each other's movement choices, had almost no measurable effect on evacuation time, and concluded that evacuation efficiency depends mainly on how effectively evacuees obtain exit information, not on crowd dynamics layered on top of it. The study's own recommendation to safety planners states this plainly: priority should go to ensuring people are familiar with exit locations, rather than relying on crowd composition or interaction effects to compensate for the fact that they aren't. It should be read as convergent, not residential-specific, evidence; the underlying model is a generic pedestrian grid validated against a logistics-warehouse case study, not an apartment corridor. But a result this large, replicated across three independent research designs, a survey, a controlled VR experiment, and an agent-based simulation, is not something this book should treat as a minor footnote to corridor length or door hardware.

A simulation study of unfamiliar-occupant wayfinding modeled populations of 100, 150, and 200 people navigating to an exit with and without a wayfinding aid, and found the aid cut total evacuation time by 19.9, 23, and 32.6 percent respectively, meaning the cost of not having one, the tax unfamiliarity imposes on egress time, grows as the evacuating population grows. That is the same population range as the two-stair, 40,000 sf floor prototype this book uses elsewhere, and it points to a specific, quantified mechanism: at that scale, unfamiliarity with the second stair does not just slow the individuals who default to the wrong or the crowded stair, it very plausibly collapses a chunk of the redundancy the second stair was built to provide, since a stair nobody uses cannot relieve congestion at the stair everybody uses.

This should be stated with the same caution this book has applied elsewhere to synthesized, non-fire-incident data. NIST's own stairwell evacuation research found that standard engineering variables, pre-movement delay, travel distance, counterflow, and stairwell geometry, explain only about 13 percent of the observed variance in real evacuation speed across fire drills, and concluded that psychological and behavioral factors, including exactly this kind of route unfamiliarity, likely account for more of the variance than the engineering models currently capture. That is a reason to treat familiarity as a real and probably underweighted variable, not a reason to assign it a precise number this book cannot support. What the Song, Kinateder, and Wang studies add, taken together, is convergence from three different methods, survey, controlled experiment, and simulation, on the same conclusion NIST's field data implies: familiarity is doing more work than the engineering variables this field has traditionally modeled, and the gap between an emergency-only stair's rated capacity and its actual use under stress is a real, now multiply-documented cost this book should not credit a two-stair building for by default.

Familiarity and the decision to evacuate at all

The more consequential effect may not be on speed but on the decision itself. An occupant who is confident of the route, because there is only one, or because the second stair is one they actually use, can make the self-evacuate decision quickly once notified. An occupant who is uncertain where the second stair is, whether it reaches the ground floor, or whether it is currently smoke-free, faces exactly the kind of ambiguity the Dutch report's cited behavioral literature associates with delay: people who are uncertain tend to gather more information, check on others, or default to the route they already know before committing to move, even when that route is compromised.

That same uncertainty cuts the other way for the defend-in-place decision this chapter has already discussed. The Minnesota TAG report's defend-in-place strategy for low-rise MFDs depends on occupants who are not in the fire unit staying put behind a closed door rather than attempting the corridor. An occupant who does not know, or does not trust, that their building is designed around that strategy has no reason to choose it over trying to self-evacuate through a corridor that may already be compromised, which is precisely the failure mode documented at Grenfell Tower and referenced in the Dutch report's own discussion of the stay-in-place principle's fragility. Kinateder, Comunale, and Warren's neighbor-influence finding applies here as well as to route choice: if the go/stay decision is socially contagious in the same way exit choice is, one or two visibly evacuating neighbors could be enough to pull an otherwise-compliant defend-in-place occupant into the corridor, and a defend-in-place strategy that depends on individual occupants holding a decision under social pressure is a different, and less certain, proposition than one that only has to survive an individual's own judgment. Familiarity, in this broader sense, is not only about knowing where a stair is; it is about occupants understanding which strategy their building expects them to use, trusting it enough to follow it under their own judgment, and not being pulled off it by what their neighbors are visibly doing.

For a single-stair PAB, this ambiguity is structurally smaller on both counts. There is no second stair to be unfamiliar with, and the building offers no real defend-in-place alternative to weigh against evacuation in the first place, since the only strategy on offer is the same short, known path everyone already uses. For a two-stair building at the 40,000 sf, 200-occupant scale this book uses for comparison, the familiarity gap is a real, cited, and currently unaddressed cost against the redundancy that stair count is assumed to provide, and it is a legitimate item for this book's own list of what additional research the IAFF and other fire-service critics would find credible: a study of actual stair-choice behavior, not just stair-count compliance, in occupied two-stair MFDs.

Smoke Gaskets and the Defend-in-Place Occupant

The Minnesota TAG report's low-rise recommendation rests explicitly on a defend-in-place strategy for occupants who are not on the fire floor, or not in the fire unit: the report states that the fire resistance ratings specified for MFD fire barriers are considered adequate to serve as compartmentation for a defend-in-place strategy, given the low joint probability of sprinkler failure and compartment failure occurring together, and the short egress time available in a low-rise building. That strategy depends on the closed door between a non-fire unit and the corridor actually holding. The Dutch field tests are the closest thing to a direct test of that assumption.

The tests ran a controlled comparison: Variant 1, an ordinary closed door with no additional sealing, against Variant 5, a smoke-resistant partition built to the S200 standard, with the door and surrounding construction sealed and made as airtight as practical, representing the standard expected in new Dutch construction. In both variants, the fire-room door was opened for exactly 30 seconds at the 5-minute mark, then closed again. The result, in the report's own words: "the effect is almost identical to that of a closed door... no significant improvement or deterioration for any specific group." The gasketed, airtight door performed no better than the plain closed door for survivability in the corridor or in adjoining residences, and slightly worse in one unit, attributed to a difference between the two test fire rooms rather than the seal itself.

The report's own explanation is the point worth carrying into this book: the 30-second door-opening event, not the quality of the seal on the door while it was shut, was decisive for how much smoke reached the corridor and the neighboring units. A gasket only pays off during the interval when the door is closed and otherwise unbreached; it does nothing about the interval when someone opens it. For a defend-in-place strategy, that means the single most consequential behavior is not whether the unit's door meets S200, but whether the door to the fire unit gets opened, by whom, and for how long. Chapter 4's equivalency case for PABs and the IAFF chapter's maintenance argument both already lean on this same point from different angles; this is the direct experimental confirmation of it.

Pressure Differentials: The Mechanism and the Numbers

How pressure actually drives smoke

A fire heats the air in the compartment where it starts, and that heated air expands. The expansion pushes air and combustion gases out through every available opening. At the same time, the plume of hot smoke rises and collects at the ceiling; once that layer descends far enough to reach the top of an opening, smoke begins to flow through it. This produces a two-part flow at any door or gap: at the top of the opening, positive pressure pushes smoke out; at the bottom, the pressure in the fire room has dropped below the pressure of the corridor or the rest of the building, so fresh air is drawn in underneath. The Dutch report describes this as the neutral-plane effect, and notes that close to the fire room, temperature differences are the dominant driver of these pressure differences; farther from the fire room, the more familiar drivers, stack effect, wind pressure, and mechanical ventilation, take over.

The numbers the field tests actually measured

This is where the Dutch data gets specific enough to use directly. Peak pressure in the fire room during the ordinary closed-door tests, Variant 1, reached 60 to 170 Pa. Peak pressure in the fire room during the sealed, airtight, S200-gasketed tests, Variant 5, reached 340 to 1,010 Pa, roughly four to six times higher. Making the compartment more airtight did not reduce the pressure the fire produced; it trapped it. With fewer paths available to vent, the same heat release drove the internal pressure dramatically higher, and the report states the mechanism plainly: a higher pressure difference can push the same amount of smoke, or more, through a smaller remaining gap. Sealing the door more effectively did not eliminate the leak; in these tests it raised the pressure behind it.

That number matters for a second reason, and this is the finding this book should lead with when discussing gaskets: the standard used to certify smoke-resistant partitions and doors in the Netherlands, NEN 6075:2020, tests smoke seals at pressures of 10, 25, and 50 Pascal. The IBC tests them at 0.1 inches of water column, or 25 Pascal for reference. The airtight, gasketed fire rooms in these field tests reached peak pressures of up to 1,010 Pascal (4 in. water column), roughly forty times higher than the highest pressure the smoke gasket certification standard actually tests for in the IBC. The Dutch researchers state this directly as a limitation worth flagging to policymakers. A smoke gasket carries a certification that says nothing about its performance at the pressure a real, well-sealed compartment fire can generate. This is not a reason to abandon smoke seals as a measure; the tests still found closed doors, sealed or not, meaningfully protected adjoining units compared to an open door. It is a reason not to treat a gasket's certification rating as a guarantee of field performance, and a reason this book should recommend testing smoke seals at pressures representative of an airtight compartment fire, not only at the pressures convenient for a laboratory rig.

A smaller but equally concrete number: mechanical ventilation used during the fire service deployment phase created local pressure differences of only 2 to 10 Pa between two measuring points on opposite sides of the same corridor. That is a small number by comparison, but the report found it was sufficient to redirect smoke into a corridor "dead space" adjacent to the ventilation flow path, meaning single-digit pressure differences, well within what a poorly aimed fan or a propped door can produce, are enough to determine which units get exposed and which don't.

Why a tighter building envelope makes this worse, not better

Modern energy codes push building envelopes toward greater airtightness, for reasons that have nothing to do with fire safety. The Dutch report's finding on this point deserves a direct statement in this manuscript: the more airtight the exterior envelope is relative to the building's interior partitions, the more smoke propagates inside the building, not less. The mechanism is straightforward once the pressure physics above is applied to the whole building rather than just the fire room. Pressure generated by a fire seeks the path of least resistance to equalize. If the exterior envelope is tight, that path is not outward through the building's skin; it is inward and laterally, through whatever interior partitions, gaps, and ducts are comparatively leakier than the envelope around them, which in a residential corridor building means directly into the corridor and adjoining units. Tightening the outside of the building without equally tightening, and pressure-rating, the inside of the building does not reduce the smoke problem. It relocates the path smoke takes from outward, where it does no harm, to inward, where it does.

This is also where the Minnesota TAG report's stack-effect framing is useful context rather than contradiction. The TAG report notes that buildings over 75 feet are more subject to stack effect and are required to have smoke control and pressurized stairways as a result, and that the efficacy of stairway pressurization is highly sensitive to how many doors are open relative to what the system was designed for, degrading quickly if that assumption is violated. A PAB held to the 75-foot, roughly six-story ceiling this book recommends is operating in a height range where stack effect is a smaller contributor to the total pressure picture than it is in a true high-rise. But the Dutch data shows that height is not the only source of a meaningful pressure differential: a single sealed compartment fire in a four-story building generated pressures an order of magnitude above what a certified smoke seal is tested to withstand, with no stack effect required to produce it. Low-rise construction does not get a pass on pressure-driven smoke migration just because it is short enough to avoid stack effect; it gets a different, and in these tests a more immediate, pressure problem instead.

A Concrete Infographic for Occupant Education

The chapter on occupant behavior established that the single most decisive variable across every Dutch test variant was not hardware but what happened at a door: whether it was opened, by whom, and for how long. That is the message an occupant education campaign should carry, and it needs to reach two different audiences with two different instructions, because the correct action for someone who can self-evacuate is close to the opposite of the correct action for someone who is defending in place. The infographic below is built around that split, and around the specific field findings in this chapter: it tells self-evacuating occupants to close the door and keep moving, and tells defend-in-place occupants to keep every door closed and signal for rescue rather than attempt a smoke-filled corridor. Both columns end on the same instruction, because it is the one behavior the data shows outperforming the hardware measure most often assumed to substitute for it.

Figure: Proposed occupant education infographic, split by self-evacuation capability, built around the door-closing finding in this chapter.

This is deliberately simple enough to reproduce as a single laminated card for a unit door, a lobby posting, or a leasing-office handout, matching the production format Tom has already used for the book's LinkedIn and Substack cover graphics. The content is not aspirational; every line in both columns traces to a specific finding in this chapter or the IAFF chapter before it: close the door (Dutch Variants 1 and 5, and the 30-second door-opening finding), don't stop to gather belongings or fight the fire (the human-behavior literature cited in the Dutch report's section 1.3.2), don't default to a familiar route if it's smoky, and know where the second stair actually is before an emergency forces that decision under stress (the route-familiarity findings above), never override a self-closing device (the Dutch finding that self-closers help the average occupant and the TAG report's compartmentation-dependent defend-in-place rationale), and call and signal rather than attempt to move through a smoke-filled corridor if self-evacuation isn't possible (the TAG defend-in-place framing, combined with the Dutch finding that vulnerable occupants get the least benefit from hardware and the most benefit from a door that simply stays shut).

Practical Takeaway: What This Means for Design, Maintenance, and Occupant Education

None of this requires new invention. Every measure this chapter points toward is already available, and most cost little to add. Require corridor smoke detection tied to the general alarm independent of sprinkler waterflow, so notification doesn't arrive at the same moment the corridor already has smoke in it. Specify smoke seals for compartmentation credit, but don't rely on the certification rating alone; ask what pressure the assembly was actually tested to, and push for testing at pressures representative of a sealed compartment fire rather than the 10-to-50 Pascal range current certification covers. Treat exterior-envelope airtightness upgrades as a fire-protection decision, not only an energy one, and pressure-balance interior partitions accordingly rather than assuming a tighter building is automatically a safer one.

For occupant education, the highest-value, lowest-cost intervention this chapter identifies isn't a system at all. It's making sure every occupant of a two-stair building can actually locate the second stair before they ever need it, and building a habit around the one instruction that outperformed every piece of hardware tested here: close the door behind you. A single-stair Point Access Block gets this benefit by design, because there's only one door and one stair to know. A two-stair building has to teach it, deliberately and repeatedly, or the redundancy it was built with never shows up when it matters.

About This Book

● Title: Point Access Blocks and Life Safety: A fire life safety analysis of single stair apartment buildings for single lot development.

● Author: Tom Jaleski

● Genre/Topics: Architecture, Building Codes, Housing Policy, and Fire Safety Engineering

● Available Formats: Paperback, Kindle

Short Summary:

Point Access Blocks and Life Safety provides a rigorous fire life safety analysis of single stair apartment buildings optimized for single lot development. This technical book evaluates the relationship between modern architectural density, building codes, and critical fire safety egress design. Written by Tom Jaleski, it serves as an essential framework for architects, urban planners, and code officials looking to safely implement Point Access Blocks (PAB) in urban environments.

About the Author:

Tom Jaleski, AIA, has spent his career on a question most architects avoid: what is the building code actually trying to accomplish, and does its prescriptive text get there?

He practiced architecture for more than twenty-five years on offices, theaters, sports arenas, aircraft hangars, apartments, and hotels. Throughout, he gravitated toward life safety and toward the negotiations with building officials that most designers dread. Eventually that became the job itself.

His work lives in the gray zones of the code. That includes alternate materials and methods requests, existing and historic buildings, fire risk analyses, and performance-based arguments that let unconventional buildings get built without giving up safety. He has secured alternate compliance approvals with jurisdictions across the country, and worked on projects across the world. His fire life safety work has also taken him to Bangladesh. After the Rana Plaza collapse, he was part of a team inspecting garment factories for the Accord on Fire and Building Safety. It was a hard lesson in the gap between a code on paper and a building in use.

He holds a Master of Architecture from the Southern California Institute of Architecture (SCI-Arc) and ICC certifications as a Building Plans Examiner and Accessibility Inspector/Plans Examiner. He is also building The CodeApp, a nonprofit platform to make building code intelligence freely accessible.

This book is the argument he has been making to building officials one project at a time: a single, well-protected stair can deliver life safety equal to or better than two, and the code should say so.

Follow his latest research and analysis on single stair apartment buildings and other building code related subjects on his Substack newsletter, LinkedIn, or across the web via the official Amazon Author Profile.

Tom Jaleski