Introduction
Fire presents one of the greatest threats to property. As such, building design and construction must take into account the wide range of fire safety features.
Not only must the interiors and contents of buildings be protected from the dangers of fire; the building site itself must be planned to ensure accessibility of both fire departments and water suppliers. Building plan and construction procedures have changed considerably during the past century (Allen and Iano 12).
A century ago, design techniques and materials, such as structural steel, reinforced concrete, and slab construction, was unknown and unimagined. In that era, major fires were common occurrences in cities. Due to combustible construction and poor city planning, whole cities were often destroyed by fire. As a result of those disasters, increased attention was given to fire safety in building design. This paper examines the building materials that can withstand fire.
Fire safety in buildings through design
Before a building designer can make effective decisions relating to fire safety design, the needs of the client regarding the function of the building and the general and unique conditions that are to be incorporated into the building must be clearly identified.
Decisions regarding the fire safety design and construction of the building should be made in the following areas: life safety; property protection; and continuity of operations (Association of Fire Chiefs International 12). These objectives describe the degree to which the building should protect its occupants, property contents, continuity of operations, and neighbors.
The objectives should be quantified wherever possible, rather than stated in broad or general terms. Design considerations for life safety must address the question of who the occupants of the house are and what they will be doing most of the time. The identification of a specific function patterns and constraints is vital in designing fire protection features that recognize occupant conditions and activities (Allen and Iano 15).
There is an important question to be asked about the design of buildings with regard to protection of property. The requirements with regard to protection of property within a building are often fairly easy to identify. Materials of high value that are particularly susceptible to fire and or smoke can usually be identified in advance of building design. For instance, vital records that cannot be replaced easily or quickly can be identified in advance as needing special fire protection design considerations (Allen and Iano 19).
Continuity of operations, the third major area of building design decision-making, must take into consideration those functions conducted in a building that are vital to continuing operation, and that cannot be transferred to another location (Association of Fire Chiefs International 38).
In this regard, the owner must identify for the designer the amount of time an operation can be suspended without completely suspending total operations. Indirect loss or loss of business income must be considered as a part of this downtime. The degree of protection required in fire-safe building design varies with the number and scope of operations that are nontransferable (National Fire Protection Association 44).
When the designer and owner either consciously or unconsciously overlook or ignore the possibility of fire in the building to be constructed, the building and its occupants are endangered (Allen and Iano 28).
The broad approach to the fire-safe design of a building requires a clear understanding of the building’s function, the number and kinds of people who will be using it, and the kinds of things they will be doing. In addition, appropriate construction and protection features must be provided for the protection of the contents and, particularly for mercantile and industrial buildings, to ensure the continuity of operations if a fire should occur (Domone 35).
The fire-safety of a building will depend first on what is done to prevent a fire from staring in the building, and second on what is done through design, construction, and management to minimize the spread of fire if and when it happens. Good housekeeping is perhaps the major factor in both fire prevention and control (Allen and Iano 48).
Keeping the fuel load down only lessens the amount of material that can be ignited, but provides less material that can be consumed if a fire breaks out. Once a fire has started, its spread will depend on the design of the building, materials used in construction, building furnishings and contents, methods of ventilation, and fire suppression systems, if any (National Fire Protection Association 59).
These elements are within the decision-making authority of various members of the design team, based on the assumption that their fire-safety objectives are clearly defined by management, the owners, and other responsible partners, both from the private and public sectors.
The design and construction elements should be organized in a manner that can give a quick overview of the major aspects that must be considered for fire-safety. They should also show features that include both active and passive design and construction considerations (Association of Fire Chiefs International 62).
Two major categories of decisions should be made early in the design process of a building in order to provide effective fire-safe design. Early considerations should be given to both the interior building functions and exterior site planning. Building fire defenses, both active and passive, should be designed in such a way that the building itself assists in the manual suppression of fire (National Fire Protection Association 70).
Interior design, circulation patterns, materials used in finishing, material, and building services are all central fire-safety factors in building plan. Building design also has a major influence of the effectiveness of the fire department operations. As a result, manual fire suppression activities should be considered during all architectural design phases. One of the important considerations in building design is access to the fire area (Allen and Iano 59).
In larger and more complex buildings, serious fires over the years have brought improvements in building design to facilitate fire department operations. The larger the building, the important access for firefighting becomes. In some buildings where the fire fighters cannot function effectively, the best solution is provision of a complete automatic sprinkler system, supplemented by a standpipe system for fire department use (Domone 60).
Ventilation is of vital importance in removing smoking, gases, and heat so that fire fighters can reach the seat of ablaze. It is difficult, if not impossible, to ventilate a building unless appropriate skylights, roof hatches, and similar devices are provided when the building is constructed. Ventilation of building spaces performs the following important functions. To begin with, it protects (Allen and Iano 62).
It aids in the enhancement of the environment close to the fire by elimination of smoke and heat. This enhances fire fighters to press forward close to the fire to put it out with the least time, water, and damage (Association of Fire Chiefs International 71). It enhances control of the spread or course of fire by creating air currents that make the fire go in a specified direction.
This enables protection of the property or those occupying the building. Lastly, it helps in the provision of a release for unburned, flammable gases before they get a flammable mixture, hence, curbing a back draft or smoke explosion (National Fire Protection Association 81).
Connections for sprinklers and standpipes must be carefully located and clearly marked. The larger and taller the building becomes, the greater the volume and pressure of water that will be needed for a potential fire (Allen and Iano 65).
Water damage may be very costly unless adequate measures, such as floor drains and scuppers, have been incorporated into the building design. Confinement of a fire in a high-rise building can only be accomplished by careful design and planning for the whole building. As buildings increase in size and complexity, more dependence on suppression systems is necessary (Domone 74).
Appropriate building blueprint for fire protection should take in a number of factors outside the building itself. The building site will affect the design. Among the significant considerations are traffic and transportation conditions, fire department accessibility and water supply.
Inadequate water supply and poor spacing of hydrants have contributed to the loss of many buildings (Association of Fire Chiefs International 79). Fire department accessibility response is a vital factor in building design considerations.
Traffic access routes, traffic congestion at times of the day, traffic congestion from highway entrances and exits, and limited access highways have significant effects on fire department response distances and response time, and must be taken into account by building designers in selecting appropriate fire defenses for a building (National Fire Protection Association 87).
As such, building designers must ensure that the building is easily accessible to fire apparatus. However, such accessibility is not always possible. When apparatus cannot come close enough to the building to be used effectively, equipment such as aerial ladders, elevating platforms and water tower apparatus can be rendered useless (Allen and Iano 79).
Another important consideration in designing a house for fire safety is the water supply to the site. A building designer must ensure that the water mains are adequate and that the hydrants are properly located. The more congested the area of the building is to be located, the important it is to plan in advance what the fire department may face in its attack, if a fire occurs on the property (Domone 85).
An adequate water supply delivered with the necessary pressure is required to control fire properly and adequately. The designer must also account for the water supply demands for fixed suppression systems, such as sprinklers and standpipes. These demands may reduce the supply available to the fire apparatus (National Fire Protection Association 98).
Another consideration in the design of a building is the possibility of damage from a fire in an adjoining building. The building may be exposed to heat radiated horizontally by flames from the windows of the burning neighboring building. If the exposed building is taller that the burning building, flames coming from the roof of the burning building can impinge on and damage the exposed building (National Fire Protection Association 100).
The damage form an exposed building can be severe. It is dependent on the amount of heat produced and length of exposure, the fuel load in the exposed building, and the construction and protection of the walls and roof of the exposed building. Other factors that can contribute to this severity include the distance of separation, wind direction, and accessibility of fire fighters (Association of Fire Chiefs International 125).
Fire severity is a description of the total energy of a fire, and involves both the temperatures developed within the exposing fire and the duration of the burning. The severity of exposure is calculated on the width and height and the percentage of openings in the exposing wall areas and the estimated fire loadings of the buildings involved (Domone 79).
Building designers should be aware that blank walls, closing wall openings, use of automatic deluge water curtains, which discharge water directly on one of the vertical surfaces of the exposed building, and use of wired glass instead of ordinary glass could reduce the separation distance hazards between the exposing buildings (Allen and Iano 93).
Materials that can withstand fire: reinforced steel and concrete
The previous discussion has dealt with the considerations that should be put into place in designing a house in order to ensure that it is fire-safe. In the next section, this paper examines how buildings can be fire-safe using construction materials that can withstand fire. Construction materials that can withstand fire are found in Type I construction (Domone 86).
Type I construction, also known as fire-resistive construction is the most fire-resistive category of building construction. It is used for buildings designed for large numbers of people, buildings with a high life-safety hazard, tall buildings, large-area buildings and buildings containing special hazards. Type I construction is commonly found in schools, hospitals, and high-rise buildings (Allen and Iano 95).
A building with Type I construction can withstand and contain fire for a longer period of time than buildings with Type II, III, IV, or V. The fire resistance and combustibility of all building materials are carefully evaluated, and each building component must be engineered to contribute to fire resistance of the entire building to warrant this classification.
All of the structural members and components used in Type I construction must be made of noncombustible materials, such as steel, concrete, or limited combustible materials such as gypsum board. In addition, the structure must be constructed or protected so that there are at least two hours of fire resistance (National Fire Protection Association 129).
If a Type I building exceeds specific height and area limitations, codes generally require the use of fire-resistive walls or floors to subdivide it into compartments. A compartment might consist of a single floor in a high-rise building or a part of a floor in a large area building.
In any event, a fire in one compartment should to spread to any other parts of the building. To ensure that fire is contained, stairways, elevators shafts, and utility shafts should be enclosed in construction that prevents fire from spreading from floor to the floor or from compartment to compartment (Association of Fire Chiefs International 132).
Steel is the most vital metal used in construction of buildings. It is normally accessible and relatively cheap. Without it, construction would be restricted to enormous all-masonry buildings with domed floors, or masonry wall-bearing buildings with wooden floors. Steel is very tough. Its compressive power is equal to its tensile strength.
Its shear strength is almost equal to its tensile strength. This great strength makes steel members of comparatively small mass to hold heavy loads, mainly when used in trusses. Nevertheless, fire resistance, is a function of mass. Such tough but lightweight members have little intrinsic fire resistance (Allen and Iano 112).
Steel has several important characteristics to consider regarding its behavior in fire. To begin with, considerable elongation can occur in a steel member at normal fire temperatures. This elongation may lead to the disturbance of building components, such as masonry adjacent to the ends of the steel.
If the steel cannot get longer because of restriction, it will crumple or overturn. This can be significant when other components rest on a steel chamber. At higher temperatures, steel members completely fail, bringing about the collapse of the structure. Another characteristic of steel is that it is a good conductor. As such, it transmits heat readily (Association of Fire Chiefs International 172).
Often the first structure that comes to mind when steel is mentioned as a construction material is the high-rise building. The development of steel framing an engineering technique made it possible to erect tall buildings.
The strength of steel, the consistency of its structural characteristics, and its ability to be connected to other structural elements so that loads can be adequately transferred are all-important to the use of steel as a building material. Only a few specialized buildings, such as fiberglass buildings, that are invisible to electromagnetic radiation or less affected by corrosive atmospheres, are built without steel (Domone 116).
The fire effect on steel can be crucial to the stability of almost any of the building during a fire incident. Steel fire escapes are provided on many buildings. If, in good condition, they can be useful, not only in evacuating occupants, but also for fire department access.
Steel reinforcing bars and cold-drawn steel tendons are vital to concrete construction in providing the tensile strength that concrete lacks. Steel is used in concrete flooring systems. Corrugated steel provides ‘left in place’ forms, which are often designed to react together with the concrete under load, thus forming a composite (Allen and Iano 121).
Apart from steel, the other building material that can withstand fire is concrete. Although concrete is taken to be a contemporary building material, it has been used in the past millennia. The use of concrete has changed dramatically over the last century as poor understanding about the material, and how it is made has improved. The industry continues to evolve today as experience grows and its versatility and cost effectiveness is exploited.
The design, construction method, materials used and standards of workmanship employed in the creation of a concrete structure will vary enormously according to the date of its construction. All these factors will affect the durability of the structure, and may result in particular deterioration problems that correlate to the construction period (Macdonald 103).
The ability of concrete to withstand fire is dependent on the aggregates forming it. Concrete is made up of aggregates of various sizes, broadly categorized as fine (commonly sand), and coarse (typically crushed stone or gravel), combined with cement paste (a mixture of cement and water), which acts as a binder (Macdonald 115).
The greater proportion of concrete is aggregate, known as the filler, which is bulky and relatively cheaper than the cement. As the constituents of concrete derive from stone, it has been known variously as artificial stone, cast stone, reconstructed stone and reconstituted stone (Macdonald 117).
The most commonly used binder in modern concrete is Portland cement. Portland cement is commercially manufactured by blending limestone or chalk with clays that contain alumina, silica, lime, iron oxide and magnesia. The compounds are heated together to high temperatures. During this process, the calcium carbonate in the limestone loses carbon dioxide, leaving the lime. The products in the clays, such as alumina and silica, are what provide the hydraulic properties (Macdonald 119).
The heating process chemically combines these materials through partial melting of the silicates and vitrification on cooling to form compounds of silicates, aluminates and aluminosilicates in the form of a clinker.
This is then finely grounded to a powder. Other cementitious binders used as partial replacements for Portland cement include blast furnace, pulverized fly ash, and silica-fume cement replacement materials. The use of different binder types varies the characteristics of the concrete, in particular its permeability to water and hence its durability (Macdonald 120).
In order for concrete to withstand fire, it has to be reinforced. Concrete is known to be very strong in compression, but relatively weak in tension.
To overcome this deficiency when concrete is used as a structural building material, and to combat early shrinkage and control subsequent diurnal thermal expansion and contraction, reinforcement is included in areas where tension occurs to create reinforced concrete.
Steel and concrete posses similar coefficients of thermal expansion and form an effective composite section. Concrete is mixed wet, poured around the placed reinforcement into the formwork, and compacted or vibrated to expel air (Domone 142).
Due to the importance of assessing the fire resistance of buildings and building materials, a great deal of work has been done to develop test procedures that assess the way building materials and structural assemblies perform under fire conditions. It is important to keep in mind that these tests must be repeatable in order to obtain uniform results from different testing laboratories. There is a possibility of approximating the damage that is caused by fire in a building.
This can be achieved by examining the types and amount of materials that can burn in the building, as well as the way they are distributed. These two factors not only indicate the rate of combustion and the duration of the fire, but also the difficult that might be encountered when automatic suppression systems are activated or when manual suppression is attempted (Allen and Iano 134).
Conclusion
In conclusion, in terms of fire protection, building design and construction practices have improved over the years, but far too many buildings are still not fire-safe. Many building designers, either through ignorance of for reasons of economy, do not put the necessary precautions to ensure that buildings are fire-safe.
Highly combustibles contents, even in a well-designed building, can cause severe fire damage. Unprotected steel can fail quickly in a fire. Tests can be made to determine the ability of the structural elements of a building to withstand fire. Fire safety is taken for granted by many individuals until a serious fire occurs. Education of building designers, building owners, and the public can lead to truly fire-safe building design.
Works Cited
Allen, Edward and Joseph Iano. Fundamentals of Building Construction Materials and Methods. New York: John Wiley & Sons, 2011.
Association of Fire Chiefs International. Fire Inspector: Principles and Practice. New York: Jones & Barlett, 2011.
Domone, Peter. Construction Materials, their Nature and Behaviors. London: Taylor & Francis, 2010.
Macdonald, Susan. Concrete: Building Pathology. New York: John Wiley & Sons, 2003.
National Fire Protection Association. National Fire Codes. New York: Jones & Barlett, 2006.