The fire resisting material is having the following characters:
(a) It should not disintegrate under the effect of heat
(b) It should not expand under heat so as to introduce unnecessary stresses in the building
(c) The material should not catch fire easily
(d) It should not lose its strength when subjected to fire.
Fire resisting characters of some of the commonly used building materials are given below:
It is a bad conductor of heat. Sand stones with fire grains can resist fire moderately. Granite disintegrate under fire. Lime stone crumbles easily. Most of the stones disintegrate during cooling period after heated by fire.
Bricks can resist heat up to 1200°C. At the time of construction, if good quality mortar is used, fire resistance is extremely good.
Any structure made of timbers is rapidly destroyed in 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 timber used in the building.
Concrete has got very good fire resistance. The actual behaviour of concrete in case of fire depends upon the quality of cement and aggregates used. In case of reinforced concrete and prestressed concrete, it also depends upon the position of steel. Larger the concrete cover, better is the fire resistance of the member. There is no loss in strength in concrete when it is heated up to 250°C. The reduction in strength starts if 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 fire resistant material.
It is a good conductor of heat. Steel bars lose tensile strength. Steel yields at 600°C. They melt at 1400°C. Steel columns become unsafe during fire. Steel reinforcement weaken the reinforced concrete structures. Hence steel columns are usually protected with brick works or by encasing in concrete. Reinforcement in concrete are protected by concrete cover. Steel grills and beams are applied with fire resistant paints.
It is a poor conductor of heat. It expands little during heating. After heating when it cools, cracks are formed in glass. Reinforced glass with steel wire is more resistant to fire and during cooling process, even if it breaks, fractured glasses are in their original position.
It is good conductor of heat. It has got higher resistance to fire.
It is non-combustible material. It posseses high fire resistance.