With reference to fire, materials may be classified as combustible materials and non-combustible materials.
Combustible materials are the materials which combine exothermally with oxygen and give rise to flame at a particular range of temperature. Examples of such materials are wood, wooden products, animal products, and man-made products like fibreboard, strawboard, etc.
Non-combustible materials are those which when decomposed by heat will do so endothermically. These materials do not catch fire by or decomposed at a particular range of temperature. Examples of such materials are metal, stone, glass, concrete, clay products, gypsum products, asbestos products, etc.
The building materials have varying fire-resistant properties which are discussed below.
1. Bricks
Bricks in general have good fire-resistant property. Particularly first class bricks are fireproof and can withstand heat for a considerable length of time. As bricks are made out of clay, which is a poor conductor, can withstand heat as high as 1300°C. Special type of bricks called fire-bricks are best for use in fire-resistance constructions. In total, brick masonry is most suitable to withstand fire hazards.
2. Terracotta
Terracotta is also a clay product which has better fire-resisting properties than bricks. As the cost is high, it is used only in restricted places.
3. Stone
Although stone may resist high temperature but deteriorate due to sudden cooling. Thus stone should be used only for a limited use in buildings with reference to fire-resistance. Granite although very strong crumbles or cracks when subjected to heat. Compact sand stone has better fire-resistant capacity. But lime stone is not all desirable as fire-resistant material.
4. Concrete
As concrete is a bad conductor of heat it has high fire-resistance capability. The extent of fire resistance depends on the aggregate, density and position of reinforcement in RCC. Use of foamed slag, blast furnace slag, crushed brick, cinder, crushed limestone, etc., form the best aggregate for fire-resisting concrete.
5. Mortar
Mortar is a cheap and best incombustible material. Cement mortar is better fire-resistant than lime mortar as lime plaster is susceptible by calcination. In order to increase the fire-resistant property, the thickness may be increased. Cement mortar with surki or pozzolana shows very high fire-resistance capability.
6. Asbestos Cement
Asbestos cement is formed by combing fibrous mineral with cement. This material shows a very high fire-resistant property. The products of asbestos cement are widely used for the construction of fire-resistive partitions, roofs, etc. Any structural member formed by combing asbestos cement offer great resistance to fire, less susceptible for cracking, or disintegration at high temperatures.
7. Steel
Steel is incombustible at moderate temperatures but shows very low fire resistance at high temperatures. At high temperatures the yield stress reduces and deforms when quenched with water in the process of extinguishing a fire. That is, all the exposed steel should be protected against fire by covering them with materials like bricks, terracotta, etc.
8. Wrought-Iron and Cast-Iron
These materials have the same behaviour as that of steel. The only difference being that it has less elasticity and retains compression and tension compared to steel. Cast-iron should not be used as a fire-resistant material as it is susceptible for deterioration when subjected to cooling.
9. Aluminium
It is a poor performance material as a fire-resistant and recommended only in places where low fire risks are expected. It is a very good conductor of heat but possesses adequate tensile strength.
10. Glass
Glass is a poor conductor of heat and undergoes a very small compression or expansion. Thus it is a good fire-resistant material. But sudden change in temperature leads to cracks or fracture. But a reinforced glass possesses high melting point and thus recommended for fire-resistant doors, skylight, windows, etc.
11. Timber
In general timber is a combustible material. But it has a special property of self insulation by forming a charred face when exposed to fire which forms a protective cover. Use of timber in large sizes offers a better fire-resistance. Timber may be made fire-resistant by impregnating it with fire-retarding chemicals such as ammonium phosphate and sulphate, boric acid, zinc chloride, etc.
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