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Construction of a completely fireproof structure may turn out to be a bit costly, but it is always possible to build structures with significant fire resistance at an acceptable budget. This can be achieved by considering fire resistance requirements of buildings. For instance, choosing suitable construction materials, taking certain precautions in the construction of buildings, and installing fire alarm systems and fire extinguishers wherever necessary.
It is demonstrated that these requirements can decline the effect of the fire load in a building substantially i.e. keep fire load to the minimum possible. The term fire load indicates the amount of heat liberated in kilojoules per square metre(kJ/m2) of the floor area of any compartment by the combustion of the content of the building including its own combustible part. It is determined by multiplying the weights of all the combustible materials by their respective calorific values and dividing that with the floor area.
1. Using Suitable Materials
Properties of Fire Resistant Materials
- It should not disintegrate under the effect of heat.
- It should not expand under heat so as to introduce unnecessary stresses in the building.
- The material should not catch fire easily.
- It should not lose its strength when subjected to fire.
Fire Resistance Characteristics of Common Building Materials
There are several materials which are commonly used in the construction of buildings. Fire resistance characteristics of these materials are discussed below:
It is a bad conductor of heat. Sandstones with fire grains can resist fire moderately; Granite disintegrates under fire; Limestone crumbles easily and most of the other stones disintegrate during the cooling period after they get heated by fire.
Bricks can resist heat up to 1200°C. At the time of construction, if a good quality mortar is used to bind the bricks, fire resistance of the structure improves manifold.
Any structure made of timber gets rapidly destroyed under the action of fire. Timber enhances the intensity of fire. Use of heavy sections of timber in buildings is not desirable.
To make timber more fire resistant, the surface of timber is coated with chemicals such as ammonium phosphate and sulphate, boric acid and borax. Sometimes fire-resistant paint is applied to the timber surface used in the building to improve the resistance.
Concrete has a very good fire resistance. The actual behaviour of concrete in an event of fire depends upon the quality of cement and aggregates used during construction.
In the case of reinforced concrete and prestressed concrete, the position of steel too influences the fire resistance ability. Larger the concrete cover, better is the fire resistance of the member.
Concrete doesn't lose much of its strength up to the temperature of 250°C. The reduction in its strength starts when the temperature goes beyond 250°C. Normally, reinforced concrete structures can resist fire for about one hour at a temperature of 1000°C. Hence, cement concrete is ideally used as a fire-resistant material.
It is a good conductor of heat. Steel bars lose their tensile strength and begin to yield at the temperature of around 600°C. They completely melt at 1400°C. Steel columns become unsafe under a prolonged action of fire. Under a constant action of fire, steel reinforcement weakens the reinforced concrete structures.
Hence steel columns are usually protected with brickworks or by encasing them in concrete. Reinforcement in concrete is protected by concrete cover whereas steel grills and beams are applied with fire resistant paints.
It is a poor conductor of heat. It expands during heating and when it cools down, cracks begin to generate in glass. Reinforced glass with steel wire is more resistant to fire and during the cooling process, even if it breaks, fractured glasses stay in their original positions.
It is great conductor of heat. It has got higher resistance to fire.
It is a non-combustible material and possesses high fire resistance.
2. Taking Precautions in Building Construction
- Dimensions of building components
- Fire-protection materials
- Exit requirements as per NBC of India which involves Provision of sufficient exits to every building to permit safe escape in the case of fire, exits should be free of obstruction, and provision of adequate illumination(lighting).
3. Provision of Fire Alarm Systems and Fire Extinguishers
These are active measures used which include fire alarm and detection systems or sprinklers that require either human intervention or automatic activation. They help control fire spread and its effect as needed at the time of the fire.