Thus, besides making a building with fire resistant materials it is
equally important to plan it in such a way that the risk of panic due to smoke
and hot gasses in minimised.
1.Danger to Life of Occupants:
This danger can be taken care of by providing adequate means of escape
for the occupants so that they can reach the place of safety in the shortest
possible time in the event of a fire. Thus the building should be so planned
that it has sufficient provisions for safe exit from within the building by way
of definite escape ways, passages, corridors and stairs etc. leading to a
street or to an open space. Lifts and escalators are not considered as exits. This
is on account of the fact that from the experience in the past it is seen that
even well designed lifts failed to operate successfully in the event of fire. This
issue needs special attention in case of multi-storeyed buildings. In case
there is a fire in a particular storey, the exit provisions in the building
should be such that the occupants of the floor immediately above and below that
floor should be able to have safe exit in reasonable short time. Thus the size
of the corridor, width of staircase and the location of the staircase halls
should be suitably decided keeping the above requirement in view. National building
code has covered the topic of fire protection in details. Some of the
requirements are:
1.Every tall building should have a minimum of two stair cases.
2. The travel distance for different types of buildings should be as
under:
a. Residential, educational, and hazardous 22.5m.
b. Assembly, mercantile, industrial, storage 30 m.
c. Business
45 m.
3. No revolving door should be treated as exits except in residential and
mercantile occupancies.
4. Lifts and escalators should not be considered as exits.
2. Danger of Spread of Fire to other
areas:
This danger can be taken care by planning and designing the building in
such a manner that the fire can be contained in a limited area for sufficient
time to enable the occupants in the Janger zone to escape to place of safety. To
meet this requirement, the building should be designed in the form of series of
compartments enclosed by floors and walls. Each compartment should be so
created that it is capable of restraining fire within the compartment for appropriate
duration of time. Beside this, each stairwell, elevator and service shaft
should also be suitably treated so as to enable it to function in the form of
vertical compartment or cell extending from top to bottom of the building.
3. Danger of damage to Property:
This danger can be minimised by use of fire resisting materials and by
carrying out the construction of the structural elements like columns, beams,
floors, load bearing walls, lintels, arches etc. in such a way that at the time
of fire they should continue to function as structural elements till such time
as would enable the occupants to escape to safe places. The degree of fire
resistance necessary to prevent penetration by fire of any structural element is
related to the fire load i.e. amount of combustible materials present in the
building per sq.m. of its floor area. Keeping in view the high cost of
construction of a fire-resistant building, it is not desirable to make all
buildings fully protected against fire.
National Building Code has classified construction into four classes namely
type 1, type 2, type 3, type 4 on the basics of fire resistance offered by
building components for 4 hours, 3 hours, 2 hours and 1 hour respectively. Thus,
in construction of type 1 all the structural components of the building are
constructed in such a manner and are of such materials that, in case of outbreak
of fire, they can withstand fire as integral members of the structure for a
duration of 4 hours.
FIRE RESISTING PROPERTIES OF MATTERIALS
The fire resisting properties of the different materials commonly used
for construction purposes are described below:
1.Timber:
Timber is unique 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
treatments retards increase in temperature during fire; decreases rate of flame
spread and enables easy fire control. Usually 32 to 48 kg of chemical per cubic
metre of wood are used for moderate protection and 80 to 96 kg. per cubic metre
for high protection.
2. Brick:
First class bricks moulded from good clay can stand exposure to fire for
a considerable length of time. The properties of bricks which render them fire
resistant and the size of bricks, the method of construction and the component of
fire resistive material in bricks i.e. clay etc. 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 severe
fire, explodes and disintegrates. Lime stone is least recommended as it crumbs
and gets ruined by an ordinary fire. Only compact sand stone having fine grains
may use as it can stand the exposure to moderate fire without serous 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 tend to contact, twist or distort and thus the stability of the
entire structure is 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, terra cotta, concrete etc.
5. Concrete:
The influence of fire on concrete varies with the nature of its coarse
aggregate and its density. It has been found that aggregates obtained from
igneous rocks containing higher calcerous content, tend to crack when subjected
to fire. Coarse aggregates like foamed slag, cinder and brick are best suited
for a concrete which has to be fire resistive. It has been noticed that in an
average fire, the concrete surface gets disintegrated for a depth of about 25
mm.
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
material. However when subjected to sudden and extreme variation of temperatures,
it fractures or cracks. By the use of glass reinforced with steel wire netting,
such cracks can be minimised. 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.
FIRE RESISTANT CONSTRUCTION
In a fire resistant construction, the maximum use of non-combustible
materials should be encouraged. All the structural elements such as beams,
columns, lintels, arches, floors and roofs, load bearing walls or partition
walls etc. should be constructed in such a way that they should continue to
function as structural members at least for the period which may be sufficient
for the occupants to escape. The following additional points should be kept in
view while designing a fire resistant structure:
1.The load bearing walls or columns of masonry should be thicker in
section so that they may successfully act as fire barrier for a considerable
time.
2. As far as possible fire resisting material should be used in the
construction of flooring. If the usage of material which is likely to be
damaged cannot be avoided either due to financial or other considerations, the
following precautions should be considered:
a. In case of wooden floors, thicker joists spaced at greater distance
apart should be used.
b. Fire stops should be provided in wooden floors at suitable intervals.
3. Reinforced concrete framed structures should be preferred to steel
structures. As steel is liable to twist, sag or distort under heavy fire, the
metal should be protected by using concrete, hollow clay tiles, bricks, metal
lath and plaster etc.
4. The partition walls should similarly be of fire resistant material. In
general, R.C.C., R,B.C, metal lath and plaster, asbestos cement board, hollow
concrete or clay tiles should be used in the construction of partition walls.
In case, wooden partition has to be made fire resistant, it should be covered
with metal lath and plaster.
5. The load bearing walls, as well as non load bearing walls, should be
plastered with fire resistive mortar.
6. The ceiling should be directly attached or suspended from the floor
joists and it should be made fire resistant by fixing asbestos cement boards,
fibre boards and plaster etc. to its framework.
7. The doors, windows or exposed sides should be glazed and fitted with
reinforced glass panels.
8. As far as possible, use metal frames for doors with steel shutters.
FIRE PROTECTION REQUIREMENTS FOR MULTI STOREYED BUILDING:
Main fire protection requirements for multistoried building can be summarized as under:
1.Structure:
The structural frame work can be in R.C.C. or steel. In case of steel
structure, it will be necessary to encase the structural components by tiles,
concrete or bricks. The fire resistance of load bearing walls, columns and
beams should not be less than two hours.
2. Internal walls and partitions:
Internal walls could be in brick, hollow concrete blocks, tiles or timber.
The materials of the wall should, however, be treated in such a manner that
they should have fire resistance of not less than one hour.
3. Staircase:
The enclosing walls of the main staircase should have a fire resistance
of not less than one hour. The staircase enclosure should be of self-contained
type with one side preferably being adjacent to an external wall. Staircase
should not be arranged around the lift shaft. Access to the staircase should be
through having fire resistance of at least half an hour. The doors should be of
swing type opening in the direction of the escape. The door of the stair case
enclosure at ground floor should open out into an open space. Adequate number
of staircase should be provided to meet the travel distance requirements of the
type of building.
4. Fire escape or external stairs:
In addition to the main staircase it is necessary to make suitable
provision of fire escape in the form of external stairs. All fire escapes
should be directly connected to ground floor and their entrance should be away
from the internal staircase of the building.
5. Basements:
The basement should be property ventilated. The main staircase of the
building should preferably terminate at ground floor and as far as possible the
access to basement should be through a separate staircase. The staircase of
basements should be of enclosed type and should be of enclosed type and should
have fire resistance of not less than two hours. In case the basement is to be
used for car parking, installation of electric substation, storage of
combustible material, etc it is necessary to install sprinkler system for
extinguishing fire.
6. Water storage tank:
There should be a provision of an underground water storage tank of one
to two lakhs litres capacity exclusively meant for firefighting purposes. The
tank should have arrangement of replenishment of the water either by the
municipal mains or by tube well.
7. Fire detection and Extinguishing
system:
All multi-storeyed buildings should have adequate provisions for fire
detection for fire detection and fire extinguishing.
FIRE DETECTION AND EXTINGUSHING
SYSTEMS
1.Fire Detection System:
Also known as fire alarm system, it is an installation provided with the
aim of warning the occupants of the building of the outbreak of fire and to
call for assistance at the same time. Fire alarm system can be either manual or
automatic.
a. Manual fire alarm system:
This consists of a hand bell or similar sounding device emitting
distinctive sound when stuck. Such devices, are installed near all the main
exists and passages. In the event of fire, the device is sounded by watch man and
the occupants are thereby warned to have safe exit in shortest possible time.
b. Automatic alarm system:
This type of system, on detection of fire, starts sounding alarms or
information to the nearest control point. Beside this, the system can also
perform the function of sounding of evacuation gong, hooters or siren and to
transmit information of the fire to a remote fire station.
2. Fire Extinguishing System:
The commonly adopted fire extinguishing systems are described below:
a. Manual fire extinguishing equipment:
Portable fire extinguisher is the equipment most commonly adopted in this
category. Portable fire extinguisher can be of carbon di oxide type, large foam
generation type and so on. Depending upon the capacity, the discharge from a
fire extinguisher may last from 20 to 120 seconds. Sometimes buckets full of
water and dry sand are also installed at convenient places for taking care of
minor fires. This equipment are useful in extinguishing fire as soon as it
starts.
b. Fire hydrants:
This consists in providing a 150 mm diameter ring main outside in the
ground around the periphery of the building. Fire hydrants are provided on the
ring main. The ring main is fed from an underground water tank and it is
ensured that the water pressure available at each fire hydrants is of the order
of 3.5 kg/cm^2.
3. West riser system:
This consists in providing 100 to 150 mm dia vertical G.I. pipes at
suitable locations within the building. The pipes are also known as risers and
are fed from an underground water storage tank through a fire pump which
ensures supply of water at 3 kg/cm^2 at the topmost outlet. The wet risers have
suitable connections at each floors from where constant supply of water can be
drawn in the event of fire.
4. Sprinkler system:
In this system a network of water supply pipes are fixed to the ceiling
of the floor or roof slab. The centre spacing of the pipe is normally 3 m. the
pipes receive supply of water through header pipes normally 40 mm. in dia,
which in turn are connected and fed from water storage tank. An installation
known as sprinkler head is fitted to the pipes in ceiling at regular intervals
normally at 3m c/c. each sprinkler head is provided with as fusible plug. In
the event of fire, the fusible plug in the sprinkler nearest to fire, melts by
virtue of rise in temperature and water gushes out of the sprinkler head. The
water spray falls on the fire and helps in extinguishing the same.
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