STP685

    Design to Cope with Fully Developed Fires

    Published: Jul 1979


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    Abstract

    Since 80 to 90 percent of the combustible contents of building compartments are consumed during the period of fully developed fire, the conditions that are expected to prevail during this period should be given special attention in the design of buildings for fire safety. The primary purpose of such design is to lessen the danger of spread of fire and smoke beyond the confines of the fire compartment. To provide a sound basis for the design, the characteristics of compartment fires, the factors that determine them, and the mechanisms by which fire and smoke spread through the building are discussed in detail.

    The most common method of protecting buildings against fire spread is compart-mentation by fire-resistant boundary elements. The shortcomings of the conventional practice of fire resistance allotment are analyzed and the principles of a recommended practice, referred to as fire tolerance design, are described.

    Information on the fire resistance of building elements is usually obtained by standard tests conducted on replicas of the elements. The meaning of the test results, however, is often unclear. It is becoming more and more acceptable to procure fire resistance information either by analytical and numerical studies, or by the use of extension and prediction formulas, graphs, and tables, many of which are reproduced for the designers' convenience.

    Owing to fundamental faults in the philosophy of fire resistance testing, information on fire resistance, either from tests or other means, cannot be directly utilized in the fire tolerance design. Methods of conversion between fire resistance and fire tolerance are presented, and techniques of designing for fire tolerance in stagnant and spreading fires, without resorting to fire resistance information, are outlined.

    Because of the prominent role that convection plays in the spread of fire and smoke, design for fire tolerance does not provide the complete answer to fire safety. The use of self-closing doors, cavity barriers and fire stops, and flame deflectors, that cut off the paths of convective fire spread, is an essential part of the overall fire defense scheme.

    An effective way of attacking the problem of spread of smoke is the pressurization of the principal shafts of the building. The danger of spread of both fire and smoke is greatly reduced by fire drainage.

    The need for expert knowledge in the design for fire safety is emphasized.

    Keywords:

    active and passive defense, air flow factor, calculation of fire resistance, characterization of fires, compartmentation, compartment ventilation, composite slabs, concrete constructions, convective fire spread, creep concept, critical air flow, critical


    Author Information:

    Harmathy, TZ
    Senior Research Officer, National Research Council of Canada, Ottawa,


    Paper ID: STP34998S

    Committee/Subcommittee: E05.32

    DOI: 10.1520/STP34998S


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