FIRE RESISTANT BUILDING MATERIALS
There is now a fast-growing awareness among the architects and
engineers to plan, design and construct the buildings / house keeping the
safety of the occupants as a focal in the event of outbreak of fire. Once the
fire starts, it has tendency to ignite all the combustible materials of the surrounding
areas and if in case it is not checked it may spread to other parts of the
buildings. If the fire is not controlled within the reasonable period, it may
lead to the collapse of building.
In case of fire, it is always the fuel that causes fire and also
aggravates it. Temperature of fire and duration of fire also plays important
role. Hence the materials used in home should be such that they do not get burn
easily act as a fuel and do not cause the heavy smoke.
Most of the countries have described fire resistance in terms of hours.
i.e. 1 hour, 2 hours of fire resistance etc. As there are norms and regulation
that should be keep in mind by Architects & Engineers to design the
building /home.
Fire resisting properties of common building materials such
as stone, brick, timber, cast-iron, glass, steel and concrete are mentioned
below.
1. Timber:
Timber has unique property of
self-insulation and slow burning and offers considerable resistance to fire.
When subjected to fire, timber first gets charred to certain depth and thereafter,
this charred layer serves as insulation to check the spread of fire to the
inner portion. Additional fire resistance is achieved through impregnation of
timber with large quantities of fire retarding chemicals. The commonly used
chemicals for this purpose are ammonium phosphate and sulphate, borax and boric
acid, zinc chloride etc. This treatment retards increase in temperature during
fire decreases rate of flame spread and enables easy fire control. Usually 32
to 48 kg per cubic meter for high protection. During the recent years, a number
of fire resistant paints have also been introduced for rendering the timber
fire resistant. Paints of asbestos, magnesium sulphate, ferrous oxide etc.,
have been found to be very much effective.
2. Brick:
First class bricks molded from good clay can stand
exposure to fire for a considerable length of time. The properties of bricks
which render them fire resistant are the size of bricks, the method of
construction and the component of fire resistive material in bricks i.e., clay.
It has been well established that brick masonry construction is most suitable
for safeguarding the structure against fire hazards.
3. Stone:
The usage of stone in a fire
resistive construction should be strictly restricted to the minimum. Hot stone
when subjected to sudden cooling develops cracks and can lead to failure of
structure. Granite when exposed to server fire, explodes and disintegrates.
Lime stone is least recommended as it crumbles and gets ruined by an ordinary
fire. Only compact sand stone having grains may be used as it can stand the
exposure to moderate fire without serious cracks.
4. Steel:
Steel although incombustible has a very low fire resistance value. With the increase in temperature, the co-efficient of elasticity of the metal falls appreciably rendering the structural members soft and free to expand. When the members in this state come in contact with water used for extinguishing the fire, they lead to contract, twist or distort and thus the stability of the entire structure in endangered. It has been noticed that unprotected steel when subjected to fire, causes the collapse of the structure. Hence in a fire resistant construction, structural steel members must be suitably protected by covering them with materials like brick, terracotta, concrete etc.
5. Concrete:
6. Glass:
Glass conducts heat faster than
metal. Because of its low thermal conductivity, the change in volume on account
of expansion or contraction is very small and as such it may be considered to
be a good fire resisting materials. However, when subjected to sudden and
extreme variation of temperatures, it fractures or cracks can be minimized.
Even when the cracks are formed, the fractured glass remains in its original
position, as the embedded wire holds the cracked portion and does not allow it
to fall. The reinforced glass has a higher melting point than the ordinary
glass, and as such it is commonly used for fire resisting doors, windows,
sky-lights etc.
7. Asbestos:
Asbestos is a fibrous mineral
which is combined with Portland cement to form a material having great fire
resistive value. Asbestos cement products are largely used for the construction
of fire-resistive partitions, roofs etc. On account of its low co-efficient of
expansion and property of in-combustibility, the structural members blended
with asbestos cement possess great resistance to cracking, swelling or
disintegration when exposed to fire.
8. Plaster or Mortar:
Plaster or mortar is in-combustible and as such by
suitable choice of the type of mortar, the walls or ceiling of a building can
be made more fire resistant. Cement mortar is preferred to lime mortar as the
latter is liable to calcine. The resistance of the plaster to fire hazards can be
increased by using it in thicker layers or reinforcing the plaster with metal
laths. Gypsum plaster when applied over structural members like steel columns
etc., makes the latter have good fire resistive qualities.
