Evacuation from Fires

Paul DeCicco, Paul R DeCicco

• Publisher: Routledge
• Year: 2019
• eBook ISBN: 9781351854825
• Topic: Psychology
• Subtopic: Environmental Management
• Index: Psychology

"Evacuation from Fires, Volume II" in this important new series was developed because of the fundamental importance of removing occupants from harm's way during building fires and the need to demonstrate new analytical techniques and tools for the design and evaluation of exit requirements during fire emergencies. The corollary issue of elevator transport for evacuation and fire fighter use during fire emergencies is also discussed in this volume.

CHAPTER 1

Commentary on Fire Safety Requirements: Circulation and Fire Safety in Buildings

J. Sterling Crandall

The author distills, summarizes and explains the requirements of the BOCA National Building Code as regards fire-safe circulation in buildings. This chapter presents seven principles of fire-safe planning, including alternate routes, limited travel, adequate and unobstructed width, increasing safety, fire separation and clear definition of escape routes. Subdivision of large buildings into separate fire areas, and the impact of floor openings and atriums are touched on. Each principle includes references to specific paragraphs and sections of The National Building Code.

The possibility of fire in a building is a fact of life. Although it may be possible to design a building using only non-combustible materials for the most part, there is no practical way to discourage the occupants from filling the building with materials that will burn. And many materials like wood, fabric and plastics which are treated to slow or prevent combustion will nevertheless give off noxious and poisonous gases when they are heated by a fire. In fact, the gases given off are sometimes the result of decomposition of the “fireproofing” agent as well as the primary material. Even a building which is otherwise made of non-combustible substances like concrete and masonry, and is protected by a fire suppression system, may be loaded with combustibles like the plastic insulation on wiring, plastic piping, insulation and other elements buried in the structure which seldom are within reach of the “sprinkling” system. Unfortunately, these elements are a principle source of fire in such buildings. The survivors of a building fire can receive no consolation from the knowledge that less fortunate people died not because the building burned, but only because its contents and some unprotected components caught fire.

WHAT FIRE SAFETY MEANS

The concept of fire safety implies relative safety for the occupants and firefighters in a building, during the time that they are trying to escape from or extinguish a fire. First, and most importantly, the building must be designed so that the occupants can move in relative safety away from a fire in any location and leave the building if necessary. This implies that the elements of the building (walls, doors, ceilings and the like) will prevent the unhampered spread of fire, smoke and toxic gases to all parts of the building. Secondly, the structural integrity of the building must not be vulnerable to a fire during the period that is required for the occupants to escape and subsequently, during the period that is required for firefighters to locate the fire and bring it under control.

Evidently, these two basic requirements imply different levels of performance for some components of a building than for others. For example, a typical office partition, separating the work space for one or two persons from a larger common area and similar offices must confine the fire and smoke only for the brief period that it takes for the occupants and those in the immediate vicinity to realize that a fire has occurred and to take appropriate action. In many such cases, the criteria to be applied are restrictions on how rapidly the material of the partition may propagate a fire (the “flame spread rating”), how much smoke may be generated by the partition during combustion and how much fuel may be contributed to the fire.

In contrast, the principle structural members and those space dividing elements which secure access routes like stairs and corridors must survive a fire long enough to permit an orderly evacuation of the building and successful fire fighting without undue hazard. Building authorities commonly require such elements to be non-combustible or “slow burning” and to be designed and detailed in such a way that they will survive an intense fire of several hours duration without collapsing or allowing the fire to spread.

FIRE SAFETY FOR OCCUPANTS

Trying to predict successfully how you would act and what you would do if you suspected that a fire threatened your safety in a building may be as difficult as trying to predict your reaction to an indecent proposal. Most people have little experience on which to base such a prediction. Your reactions would probably depend on your certainty about the probable danger, how you were feeling at the time, the behavior of others who might be watching you for cues and any number of other related matters. On the other hand, everyone has had enough experience with false alarms to be able to predict with high probability of success that the next time the fire bell rings, it will be another false alarm. Consequently, the first reaction most of us have to a fire alert is more likely to be curiosity than an immediate impulse to get out of the building. Unfortunately, the one or two minutes that are needed to “check it out” may be the difference between survival and disaster in a real fire situation.

Everyday experiences such as “quitting time” and “fire drills” lead people to believe that all of the occupants of a large building can evacuate in a few minutes. At such times, their expectations are fulfilled more often than not. But these events do not reproduce the conditions of panic, confusion and disorientation that are commonplace in a fire. To evacuate a building quickly people must have a compelling reason to leave immediately, they must be able to find the way out easily, and they must meet no obstacles along the way. But hazardous design features of a building often do not become apparent excepting in the context of fire conditions. And in spite of the most conscientious attention to fire safety in the planning of a building, occupants often circumvent important safeguards by blocking fire doors in the open position, disabling smoke detectors, etc. It falls to the designer of buildings to insure by the way the building is planned that the exit paths are obvious and the routes to safety are secure, even under the most unfamiliar and threatening conditions. At least then, those who run in the direction of the smoke to find out if the smoke is coming from a fire will have a better chance to recover from their error.

A building design which provides fire safety for the occupants will have several distinctive, discernible characteristics. These are listed briefly below and will be elaborated later as design principles which are reflected by detailed fire protection and egress requirements written into model building codes.

1. A fire safe building has alternate escape routes from nearly every location which might be occupied. In general, the alternate routes lead in different directions to different exitways and through such exitways to a public right-of-way.

2. No occupant must travel very far to put effective fire barriers between self and those locations where fires are likely to occur. In practice, the maximum distance permitted is specified.

3. There are no obstructions or constrictions along the escape routes, including those parts of the route which must be traversed in order to get to a corridor or stair. The escape routes are wide enough at all locations to accommodate rapid movement of the occupants in orderly files.

4. Escape routes proceed from every location in the building towards exits through increasingly safe spaces. Safety is evaluated by considering the use of the spaces encountered along the route and the degree of protection provided by fire barriers which separate the escape route from fire hazard.

5. Exitways (corridors, stairs, lobbies and the like which lead out of the building) are protected from the potentially hazardous spaces which they traverse by fire assemblies (a collection of building elements including partitions, doors, floor slabs, ceilings, self closing dampers and the like).

6. The exit discharges (from exitways) are clearly defined, not only by the usual signs and lights, but by the character of the planning that has been done. In unprotected spaces, the location of exits is also clearly defined. The character of the exitway is not likely to confuse and mislead occupants, even though they may be frightened, unable to see and physically distressed.

7. Very large buildings are divided by effective barriers (fire walls) to insure that fire, smoke and superheated air cannot spread rapidly throughout an enormous area, closing off all possible escape routes before many occupants are aware of the danger.

PRINCIPLE 1: MULTIPLE ESCAPE ROUTES

Escape route is not recognized code terminology. An escape route includes the unprotected part of the path to an exit (which is called “exit access travel” in the BOCA Code), as well as any protected corridors or stairs, lobbies, vestibules and exterior doors comprising the “exitway” and “exitway discharge.” In general, the number and width of building escape routes and their elements are governed by the use and occupancy load of the building. Similarly, the required number and width of escape routes from individual spaces varies, depending on the use of each space and the number of occupants. Each escape route must terminate outside the building in a space accessible from a public right of way.

An escape route leading to an enclosed court is not permitted unless it is possible to get from the court to a public right of way without going back into the building. We assume that the windows opening onto such a court would break during a severe fire, and the smoke and gases of the fire would be driven into the court by cooler, denser air from the area surrounding the building. Thus, an enclosed courtyard may be as dangerous as the building itself, perhaps more so.

As a rule, each space and each building must provide at least two well-defined escape routes. However, specific exceptions to this rule are written into every model building code, and municipal building authorities as well as other regulatory agencies amend the model codes to fit local and regional interpretations [1].

PRINCIPLE 2: LIMITED ESCAPE DISTANCE

People can tolerate exposure to the heat, smoke and gases generated by a fire for only a brief period. By limiting the distance that must be traveled through unprotected spaces, the designer provides some insurance that the occupants will be able to reach a safe place before they collapse. In a large building, it is assumed that principle corridors and stairs are protected from the spread of fire or the diffusion of smoke by appropriate fire assemblies, e.g., self-closing doors, fire dampers, sprinklers and the like. In this case, a person who has reached such a corridor or stair is considered to be relatively safe: the unprotected travel occurred before entering the corridor or stair.

However, many things can go wrong with the systems that are intended to secure the corridors and stairs. Door closers may be disabled. Fire dampers may be omitted. Large areas of glass may be incorporated in the partitions or doors which separate the corridors from the rest of the building. Combustible furnishings may be placed in lounges or waiting areas which are incorporated in exit corridors and stairs. Changes in use may rearrange the partitions which separate a corridor from the rest of a floor, with the result that the corridor is no longer a safe exit. The designer may have had a hand in some of these decisions, or they may have been made without the knowledge or approval of the designer.

Such decisions are much more likely to affect corridor protection than stair protection. To provide some flexibility in the use of each floor area, both in the initial design process and for the sake of subsequent modifications, the designer may want to plan the building so that the travel distances from any point on a floor to the nearest enclosed stair do not exceed the maximums permitted by the building code. When there is no separation of the escape route from the rest of the building (unenclosed corridors and stairs), a condition permitted in certain cases by most building codes, then the travel distance from each point in the building must be measured to the nearest exterior door leading to a public right of way.

The travel distance to protected exitways must be measured along the “natural and unobstructed line of travel” from each location in a building to the exit nearest that location. When stairs or ramps are encountered along the route in question, the distance along the slope is to be included as the “vertical” component [2].

PRINCIPLE 3: UNOBSTRUCTED ESCAPE ROUTES

The width of the circulation paths which will be used as escape routes from a building is governed by the number of occupants who are likely to employ each route simultaneously. The combined number and width of all the escape routes from a single floor must be sufficient to allow all of the occupants of the floor to reach an exit in little more time than it takes one person to walk rapidly the maximum (permitted) exit access travel. In theory, this means that everyone in a building could reach an exit in less than one minute, traveling at two miles per hour.

One way to appreciate the interaction between the required number of exits from a building (or part of a building) and the width of those exits is to envision all of the occupants lining up in single file columns to leave the building. Each single file column will be 22 inches wide (the average width of a person across the shoulders) and no longer than the maximum permitted access travel distance (so that the last person in line can reach an exit in less than a minute). Walking rapidly, each person in line will take up about two feet of length, thus the number of occupants that can be accommodated by one 22 inch unit of exit width is one-half of the maximum permitted access travel distance (in feet).

People who require assistance and people traveling on stairs or ramps cannot move as quickly as able-bodied persons on level surfaces. Thus, the length of the single-file columns must be reduced for these conditions, and the number and width of exits necessary to accommodate all of the occupants will increase.

Calculating the number and width of exits required for a building is complicated by the fact that the escape routes provided by the design (and every element encountered along the way, such as corridors, stairs and doors) must be compared with the units of exit width required instead of the number of inches or feet. Thus, the units provided by each element must be determined first. In the case of multiple elements, like a pair of adjacent doors, the units provided by each must be determined separately, and then the units added together to get the total units provided by the doors combined. Often this results in overall openings or passages which are wider than they would have to be if they were combined into one. The conversion from inches to units of exit width is as follows (in The BOCA National Building Code), and continues in disorderly fashion:

Exit Width (inches)

Units of Ex...

Table of contents

• Cover
• Title Page
• Copyright Page
• Table of Contents
• Introduction
• CHAPTER 1 Commentary on Fire Safety Requirements: Circulation and Fire Safety in Buildings
• CHAPTER 2 High-Rise Office Building Evacuation Planning: Human Factors Versus “Cutting Edge” Technologies
• CHAPTER 3 An Investigation of the Aspects of Occupant Behavior Required for Evacuation Modeling
• CHAPTER 4 Adaptive Decision-Making in Response to Crowd Formations in buildingEXODUS
• CHAPTER 5 T-HELP: A Mathematical Model for Calculating Time Available for Escape from Fire
• CHAPTER 6 A Consideration on Required Number of Exits in a Room
• CHAPTER 7 Illustrating Some Rule Based Algorithms of Egress Complexity Using Simple Case Studies
• CHAPTER 8 The Impact of a Wheelchair Bound Evacuee on the Speed and Flow of Evacuees in a Stairway During an Uncontrolled Unannounced Evacuation
• CHAPTER 9 A Study on the Exit Requirements in Karaoke Establishments
• CHAPTER 10 Perspective on Elevator Safety During Fires
• Contributors
• About the Editor
• Index