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Practically no building is perfectly fire-proof. Because every building contains some materials which can catch fire easily. The perspective of the architect or engineer should be to plan, design, and construct the building such that it ensures the safety of occupants from the outbreak of fire due to any reason. The fire resistance of a building is expressed in terms of hours when it is subjected to fire of known intensity. Fire protection word is used to cover the following aspects:
Most of the outbreaks of fire are caused by carelessness. In case of an outbreak of fire, the danger is from fire, smoke, and panic. The prevention methods should be in relation to these dangers and the number of persons affected.
There are three aspects that are considered in the fire safety of buildings and accordingly, protection should be provided against these hazards.
1) Personal hazards i.e., the possibility of loss or damage to life.
2) Internal hazards, i.e., the possibility of a fire occurring and spreading inside the building itself.
3) Exposure hazards, i.e., the possibility of fire spreading from an adjoining building.
Personal hazards are naturally considered as of permanent importance and it requires the provision of liberally designed and safe exit escapes in all buildings, especially in multi-storeyed buildings.
An internal hazard directly influences personal hazards and it concerns damage or destruction of buildings. It is directly related to fire load, which enables the building to be graded when considered along with the duration of the fire.
Exposure hazards deal with the risk of fire spreading into a building through the open air from fire in other buildings for example, from the stocks of combustible material or from a division or apartment of a building through the open air from a fire in another division or apartment of the same building.
A small building containing highly inflammable materials may constitute a high internal hazard; a large building for example godown is also described as high internal hazards because it contains a large no of materials. Theatre, cinema halls, and other places of public assembly even though their combustible contents are low, but considered as having high internal hazard. It is because of the large no of people and the extent of personal hazards involved.
Fire load is the amount of heat liberated per square meter of the floor area of any compartment by the combustion of the contents of the building. It is expressed in terms of kilocalories (kcal) per square meter. The amount of heat is used as the basis of grading of occupancies.
Indian Standards (IS: 1641-1988) has provided the grading of fire loads into three classes.
Fire safety requirements in a building:
IS:1641-1988 recommends that the buildings should conform to the following requirements in order to minimize fire hazards. These are-
Characteristics of fire-resisting materials:
Fire resisting materials should possess some characteristics. These are described below:
Building materials can be divided into two types: combustible materials and non-combustible materials. Combustible materials are those which help in the growth of the fire. During a fire, these materials combine exothermally with oxygen resulting in the evolution of heat and resulting in the evolution of a lot of heat and giving rise to flame or glow. Non-combustible materials do not contribute to the growth of a fire. They decompose by absorption of heat and oxidize by negligible evolution of heat.
Fire resisting properties of common building materials:
Stone -Stone is a non-combustible building material and it does not contribute to the spread of fire. But, it is a bad fire-resisting material because it disintegrates into small pieces when heated and suddenly cooled, giving rise to the failure of the structure. Granites undergo disintegration on severe heat and explode. Limestone is the worst in this case. Sandstone can withstand exposure without serious cracks.
Bricks:-It is a poor conductor of heat. First-class brick can stand the exposure to fire for a considerable length of time up to the temperature of 1200
Concrete:-The fire-resisting property of concrete depends upon the nature of coarse aggregate, its density, and the quality of cement. It also depends upon the position of steel in concrete. Aggregate expands on heating and ordinary cement shrinks during heating. Due to these two opposite actions, the concrete surface undergoes spalling. Generally concrete offers a much higher resistance to fire than any other building materials. Reinforced concrete can withstand fire for several hours up to a temperature of 1000 without serious damage.
Steel:-Steel has very low fire resistance because it is a good conductor of heat. During a fire, it gets heated very soon; its modulus of elasticity reduces and loses its tensile strength rapidly. It is found that the yield stress of mild steel at 600 is about half of its value during normal temperature. That is why unprotected beams sag and unprotected columns or struts buckle. It results in the collapse of the structure. It is essential to protect structural steel members with some coverings of insulating materials like brick, terracotta, concrete, etc.
Timber:-It is a combustible material. It ignites and gets rapidly destroyed during a fire if the section is small. If the section is thick, it possesses properties of self-insulation and slow-burning. In order to make timber fire-resistant, the following measures are adopted.
In a fire-resistant construction, the design should be such that the components of the building can withstand the fire as an integral member. We should consider the following construction:
Walls and columns:
Masonry walls and columns should be made of thicker sections so that they can resist fire for a long time. For solid load-bearing walls, bricks should be preferred to stones. In the case of stones, granite and lime stones should be avoided. In the case of buildings with framed structures, RCC should be preferred to steel. All walls whether load-bearing or not should be plastered with fire-resistive mortar.
Floors and roofs:
For better fire resistant slab roof is preferred to a sloping or pitched roof. In the case of a sloping roof, trusses should be of RCC or of protected rigid steel with fireproofing. The floor should be of RCC or hollow tiled ribbed floor. Suitable fire-resistant materials for flooring are tiles, ceramic tiles, bricks, etc. ceiling, directly suspended from floor joists should be of fire-resistant materials like asbestos cement boards, fibre boards, metal lath with plaster etc.
Openings serve the means of escape. These should be properly protected by suitable arrangements. Doors and windows should be made of steel. Wire glass panels are preferred for windows. All escape doors should provide free circulation to the persons in the passage.
All escape elements such as staircases, corridors, lobbies, entrances, etc. should be made of fire-resistant materials. Lift shafts should be vented from top to permit the escape of smoke and hot gases. An emergency ladder should be provided in the fire-resisting building. This ladder should be at least 90 cm wide. All escape routes should be protected with railings, balustrades, or parapets.
Strong room construction:
A strong room is found to be useful in the case of safe deposit vaults in banks. The walls, ceilings, floors of a strong room should be made of at least 30 cm thick cement concrete. Windows and ventilators should be covered by special grills made of 20 mm steel square bars. The grills should be well fixed to concrete walls by means of long steel holdfasts.
Fire alarms and fire extinguishing equipment:
Fire alarms are installed in buildings to give an alarm and to call for assistance in event of fire. It gives enough time to the occupants to reach a safe place. Two types of fire alarms are there: manual alarms and automatic alarms.
Every building should have suitable fire extinguishing equipments depending upon the importance of the building. These are: