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Building protection against fire

There are two distinct aspects of building fire protection: life safety and property protection. Although providing for one aspect generally results in some protection for the other, the two goals are not mutually inclusive. A program that provides for prompt notification and evacuation of occupants meets the objectives for life safety but provides no protection for the property. Conversely, it is possible that adequate building protection might not be sufficient for the protection of life.

Absolute safety from fire is not attainable. It is not possible to eliminate all combustible materials or all potential ignition sources. Thus, in most cases, an adequate fire protection plan must assume that unwanted fires will occur despite the best efforts to prevent them. Means must be provided to minimize the losses caused by the fires that do occur.

The first obligation of designers is to meet legal requirements while providing the facilities required by the client. In particular, the requirements of the applicable building code must be met. The building code will contain fire safety requirements, or it will specify some recognized standards by reference. Many owners will also require that their own insurance carrier be consulted—to obtain the most favorable insurance rate, if for no other reason.

Building Fire-Protection Standards

The Building Fire Protection standards most widely adopted are those published by the National Fire Protection Association (NFPA), Batterymarch Park, Quincy, MA 02269. The NFPA ‘‘National Fire Codes’’ comprise several volumes containing numerous standards, updated annually. (These are also available separately.) The standards are supplemented by the NFPA ‘‘Fire Protection Handbook,’’ which contains a comprehensive and detailed discussion of fire problems and much valuable statistical and engineering data.

Underwriters Laboratories, Inc. (UL), 333 Pfingsten Road, Northbrook, IL 60062, publishes testing laboratory approvals of devices and systems in its ‘‘Fire Protection Equipment List,’’ updated annually and by bimonthly supplements. The publication outlines the tests that devices and systems must pass to be listed. The UL ‘‘Building Materials List’’ describes and lists building materials, ceiling-floor assemblies, wall and partition assemblies, beam and column protection, interior finish materials, and other pertinent data. UL also publishes lists of ‘‘Accident Equipment,’’ ‘‘Electrical Equipment,’’ ‘‘Electrical Construction Materials,’’ ‘‘Hazardous Location Equipment,’’ ‘‘Gas and Oil Equipment,’’ and others.

Separate standards for application to properties insured by the Factory Mutual System are published by the Factory Mutual Engineering Corporation (FM), Norwood, MA 02062. FM also publishes a list of devices and systems it has tested and approved.

The General Services Administration, acting for the federal government, has developed many requirements that must be considered, if applicable. Also, the federal government encourages cities to adopt some uniform code. In addition, buildings must comply with provisions of the Americans with Disabilities Act (ADA). (See Department of Justice final rules, Federal Register, 28 CFR Part 36, July 26,
1991; American National Standards Institute ‘‘Accessibility Standard,’’ ANSI A117.1; ‘‘ADA Compliance Guidebook,’’ Building Owners and Managers Association International, 1201 New York Ave., Washington, D.C. 20005.)

The Federal Occupational Safety and Health Act (OSHA) sets standards for protecting the health and safety of nearly all employees. It is not necessary that a business be engaged in interstate commerce for the law to apply. OSHA defines an employer as ‘‘a person engaged in a business affecting commerce who has employees, but does not include the United States or any State or political subdivision of a State.’’

An employer is required to ‘‘furnish to each of his employee’s employment and a place of employment which is free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees.’’ Employers are also required to ‘‘comply with occupational safety and health standards promulgated under the Act.’’

Building codes consist of a set of rules aimed at providing reasonable safety to the community, to occupants of buildings, and to the buildings themselves. The codes may adopt the standards mentioned previously and other standards concerned with fire protection by reference or adapt them to the specific requirements of the community. In the absence of a municipal or state building code, designers may apply the provisions of the Uniform Building Code, promulgated by the International Conference of Building Officials, or other national model codes.

Many states have codes for the safety of life in commercial and industrial buildings, administered by the Department of Labor, the State Fire Marshal’s Office, the State Education Department, or the Health Department. Some of these requirements are drastic and must always be considered.

Obtaining optimum protection for life and property can require consultation with the owner’s insurance carrier, municipal officials, and the fire department. If the situation is complicated enough, it can require consultation with a specialist in all phases of fire protection and prevention. In theory, municipal building codes are designed for life safety and for the protection of the public, whereas insurance-oriented codes (except for NFPA 101, ‘‘Life Safety Code’’) are designed to minimize property fire loss. Since about 70% of any building code is concerned with fire protection, there are many circumstances that can best be resolved by a fire protection consultant.

Building Fire-Protection Concepts

Although fires in buildings can be avoided, they nevertheless occur. Some of the reasons for this are human error, arson, faulty electrical equipment, poor maintenance of heating equipment, and natural causes, such as lightning. Consequently, buildings should be designed to minimize the probability of a fire and protect life, and limit property damage if a fire should occur. The minimum steps that should be taken for the purpose are as follows:

  1. Limit potential fire loads, with respect to both combustibility and ability to generate smoke and toxic gases.
  2. Provide means for prompt detection of fires, with warnings to occupants who
    may be affected and notification of the presence of fire to firefighters.
  3. Communication of instructions to occupants as to procedures to adopt for
    safety, such as staying in place, proceeding to a designated refuge area, or
    evacuating the building.
  4. Provide means for early extinguishment of any fire that may occur, primarily
    by automatic sprinklers but also by trained firefighters.
  5. Make available also for fire fighting an adequate water supply, appropriate
    chemicals, adequate-size piping, conveniently located valves on the piping,
    hoses, pumps, and other equipment necessary.
  6. Prevent the spread of fire from building to building, either through adequate sep-
    aeration or by the enclosure of the building with incombustible materials.
  7. Partition the interior of the building with fire barriers, or divisions, to confine
    a fire to a limited space.
  8. Enclose with protective materials structural components that may be damaged
    by fire (fireproofing).
  9. Provide refuge areas for occupants and safe evacuation routes outdoors.
  10. Provide means for removal of heat and smoke from the building as rapidly as
    possible without exposing occupants to these hazards, with the air-conditioning system, if one is present, assisting the removal by venting the building and by pressurizing smokeproof towers, elevator shafts, and other exits.
  11. For large buildings, install standby equipment for operation in emergencies of
    electrical systems and elevators.

Fire Loads and Resistance Ratings

The nature and potential magnitude of fire in a building are directly related to the amount and physical arrangement of combustibles present, as contents of the building or as materials used in its construction. Because of this, all codes classify buildings by occupancy and construction, because these features are related to the number of combustibles.

The total amount of combustibles is called the fire load of the building. Fire load is expressed in pounds per square foot (PSF) of floor area, with an assumed calorific value of 7000 to 8000 Btu/lb. (This Btu content applies to organic materials similar to wood and paper. Where other materials are present in large proportion, the weights must be adjusted accordingly. For example, for petroleum products, fats, waxes, alcohol, and similar materials, the weights are taken at twice their actual weights, because of the Btu content.)

National Institute of Standards and Technology burnout tests presented in Report BMS92 indicate a relation between fire load and fire severity as shown in Table 3.2.

The temperatures used in standard fire tests of building components are indicated by the internationally recognized time-temperature curve shown in Fig. 3.9. Fire resistance of construction materials, determined by standard fire tests, is expressed in hours. The Underwriters Laboratory’s ‘‘Building Materials List’’ tabulates fire ratings for materials and assemblies it has tested.

TABLE 3.2 Relation between Weight of Combustibles and Fire Severity*

Average weight of combustibles, psfThe average weight of combustibles, psf
Table: Based on National Institute of Standards and Technology Report BMS92, ‘‘Classifications of Building Constructions,’’ Government Printing Office, Washington, D.C. 20402.
image/svg+xml TIME , HR TEMPERATURE, °C TEMPERATURE, °F 0 200 400 600 800 1000 1200 0 2 4 6 8 0 400 800 1200 1600 2000 2400

Figure 3.9: Time-temperature curve for a standard fire test.

Every building code specifies required fire-resistance ratings for structural members, exterior walls, fire divisions, fire separations, ceiling-floor assemblies, and any other constructions for which a fire rating is necessary. Building codes also specify the ratings required for the interior finish of walls, ceilings, and floors. These are classified as flame spread, fuel contributed, and smoke developed, determined in standard tests performed according to ASTM E84 or ASTM E119.

Building Fire and Smoke Barriers

A major consideration in building design is the One way that building codes try to achieve this objective is to establish fire zones or fire limits that restrict types of construction or occupancy that can be used.

Additional zoning regulations establish minimum distances between buildings. Another way to achieve the objective is to specify the types of construction that can be used for enclosing the exterior of buildings. The distance between adjoining buildings, fire rating, stability when exposed to the fire of exterior walls, windows, and doors, and percent of window area are some of the factors taken into account in building codes for determination of the construction classification of a building. safety of the community. Hence, buildings should be designed to control fires and smoke so that they will not spread from building to building.