7. FIRE-RESISTING CONSTRUCTION
A fully fire resistant building is fully protected against any fire which occur in is contents.
Causes of Fire: The causes of various types of fire hazards are described in details:
• Electrical hazards: Damaged wiring, Damaged plugs, Damp or wet wires, Overloaded motors, Broken switches, outlets or sockets, Problems with lighting fixtures, Faulty heating elements, Overloaded circuits, Liquids near computers, Computers without surge
protectors.
• Housekeeping hazards: Piles of scrap, waste materials, and trash; Sawdust, metal or
plastic powder that can form an explosive mixture with air; Obstructed aisles, Blocked emergency exits, Material covering up fire extinguishers, exit signs, and alarms; Blocked sprinkler heads.
• Friction hazards: Hot bearings, Misaligned or broken machine parts, choking or jamming materials, Poor adjustment of moving parts, Inadequate lubrication.
• process or operation-related hazards: Cutting and welding operations, which use open flames and produce sparks; Molten metal, which can ignite combustibles or fall into cracks and start a fire that might not erupt until after the work is done; Processes that heat materials to high temperatures; Drying operations where materials in dryers can overheat; Grinding operations that produce sparks and dust; Processes in which flammable vapors are released
• Storage hazards: Materials stacked too high blocking sprinkler heads (need 18-inches clearance from head); Flammable or combustible materials stored too close to heat sources; Flammable materials not stored in special containers and cabinets Inadequate ventilation in storage areas; Materials that might react with one another stored together; Materials stored in damaged containers; Materials stored in unlabeled containers; Containers not tightly sealed
• Smoking hazards: Ignoring "No Smoking" signs; Smoking around flammable or combustible materials; Throwing matches and cigarettes or cigars on tables or workbenches; Tossing butts on the floor or grass without properly extinguishing them in
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an ashtray or ash can; Tossing lighted butts or matches out windows or doors; Smoking in bed; Leaving a cigarette/cigar unattended; Smoking in areas where there is an accumulation of sawdust, plastic or metal powders that may become explosive.
Fire Load: It is the amount of heat liberated in KJ/m2 of floor area of any component by the combustion of the content of and any combustible part of building itself. The classification of fire load as per BIS: 1641-1960 are as follows:
1. Low fire load: not exceeding 1.15× 106 KJ/m2
2. Moderate fire Load: 1.15× 106 KJ/m2 to 2.30× 106 3. High fire Load: 2.23× 106 KJ/m2 to 4.60× 106
Limiting Fire Load:
1. Providing fire Fighting Equipment
2. Using fire resistant materials for construction
3. Providing suitable means of escape
4. Protection of openings
Characteristics of fire resisting materials:
• • •
The composition of the material should be such that it does not become disintegrated under the effect of great heat.
The expansion of the material due to heat should not be such that it leads to instability of the structure.
The contraction of the material due to the sudden cooling with water after it has not been heated to a high temperature should not be rapid.
Fire resisting properties of common building materials:
Fire resisting properties of common building materials such as stone, brick, glass, steel and concrete are described below:
a. Stone: stone is a bad conductor of heat and it is also a non-combustible material;
however, it suffers appreciable under effect of fire. Moreover, the stone is also liable to
disintegrate in to small pieces when heated and suddenly cooled.
b. Brick: Bricks are not seriously affected until very high temperatures around 1200 oC to
1300 oC are reached. This is due to the fact that a brick is poor conductor of heat.
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c. Cast-iron: The material files in to pieces when heated and suddenly cooled. Therefore, when this material in construction. It is covered either by brickwork of one- brick thickness or any other fire resisting material such as construction.
d. Timber: Generally, the structural elements made of timber ignite and get rapidly destroyed in case of fire. To increase the timber more fire resisting, the surfaces of timbers are coated with chemicals such as ammonium phosphate and sulphate, borax and boric acid, zinc chloride.
e. Glass: The materials are poor conductor of heat and its expansion due to heat is small. The cracks are formed in this material when heated and suddenly cooled.
f. Wrought- iron: This material is rarely used as structural as present. It behaves more or less in the same way mild steel.
g. Aluminium: Very good conductor of heat, it possess poor fire resisting properties.
h. Asbestos Cement: this is non-combustible building material with low coefficient of
expansion. It therefore possesses high fire resisting property than other material.
Fire Protection System: The system which protects a large area from fire by using components such as pipes, pump sets, control panel, sprinklers or nozzles etc,, is known as fire protection system.
1. Automatic sprinkler system: Most reliable automatic means of fire fighting. It involves
automatic sprinklers attached to a piping system containing water under pressure and connected to a water supply so that water is discharged immediately sprinkler opened by fire.
2. Carbon dioxide system: It extinguishes fire by diluting flammable mixture of air and flammable gas or vapour to proportions below their flammable limits.
3. Dry Chemical system: This system includes a supply of dry chemical, an excellent gas such as compressed nitrogen detection devices, release mechanism, fixed piping and nozzles for discharging the dry chemical into hazard area.
4. Foam System: In this system, the mechanical foam is formed by passing foam producing liquid and water through adequate device. The foam is as aggregate of air filled bubbles. It is lighter than flammable liquids and oils. The principal components of this system include proportioning apparatus, concentrated storage tank, water supply, foam maker or spray foam-heads, heat detecting devices, automatic and manual actuation devices and an alarm system.
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5. Holon System: This indicates a specific family of chemicals which are produced by replacing one or more hydrogen atoms with halogen atoms. This is contained in cylinders under pressure in liquid state and it is released through nozzles on piping distribution arrangement. An actuator is provided a cylinder control value and it is operated either by electric or pneumatic signal when fire occurs.
6. Hydrant system: in this system, the hydrants are located at suitable points and they can be operated at suitable points and they can be operated manually or automatically.
7. Water Spray System: The water spray system used for fire extinguish depends upon the type of spray and can be sprayed in two categories:
• Multi-fire system: water is sprayed in high velocities
• Protective System: Fine water spray of low discharge velocity
Various types of Fire-resisting construction:
The type and age of construction are crucial factors to consider when assessing the adequacy of existing escape routes. To ensure the safety of people it may be necessary to protect escape routes from fire. In older premises it is possible that type of construction and materials used may not perform to current fire standards and refurbishments may have led to:
• Cavities and voids being created, allowing the potential for the unseen spread of fire. • Doors and hardware being worn by age and movement being less likely to limit the
spread of fire and smoke.
• Damaged or insufficient cavity barriers in modular building construction (e.g.
CLASP or SCOLA type construction).
• Breaches in fire compartment walls, floors and ceilings created by the installation of
new services, (e.g. computer services).
Where an escape route requires the provision of fire resisting construction (e.g. dead end corridors or protected stairways) the following should be ensured:
• Doors (including access hatches to cupboards, ducts and vertical shafts linking floors), walls, floors and ceilings protecting escape routes should be capable of resisting the passage of flame and smoke for long enough for people to escape from the building (normally 30 min).
• Where false ceilings are provided, fire resistance should extend up to the floor slab above (for means of escape purposes 30min fire resistance is required).
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• Cavity barriers, fire stopping and dampers in ducts are appropriately installed as required.
General
The materials from which your premises are constructed may determine the speed with which a fire may spread, affecting the escape routes that people will use. A fire starting in a building constructed mainly from readily combustible material will spread faster than one where modern fire-resisting construction materials have been used. Where non- combustible materials are used and the internal partitions are made from fire-resisting materials, the fire will be contained for a longer period, allowing more time for the occupants to escape. Because of the requirements of the Building Regulations you will probably already have some walls and floors that are fire-resisting and limitations on the surface finishes to certain walls and ceilings.
You will need to consider whether the standard of fire resistance and surface finishing in the escape routes is satisfactory, has been affected by wear and tear or alterations and whether any improvements are necessary.
The following paragraphs give basic information on how fire-resisting construction can provide up to 30 minutes protection to escape routes. This is the standard recommended for most situations. If you are still unsure of the level of fire-resistance that is necessary after reading this information, you should consult a fire safety expert.
Fire resisting construction
The fire resistance of a wall or floor is dependent on the quality of construction and materials used. Common examples of types of construction that provide 30-minute fire resistance to escape routes if constructed to the above standards are:
• Internal framed construction wall, non-load bearing, consisting of 72mm x 37mm timber studs at 600mm centres and faced with 12.5mm of plasterboard with all joints taped and filled.
• Internal framed construction, non load- bearing, consisting of channel section steel studs at 600mm centres faced with 12.5mm of plasterboard with all joints taped and filled;
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• Masonry cavity wall consisting of solid bricks of clay, brick earth, shale, concrete or calcium silicate, with a minimum thickness of 90mm on each leaf.
There are other methods and products available that will achieve the required standard of fire resistance and may be more appropriate for the existing construction in your premises. If there is any doubt about how your building is constructed, then ask for further advice from a competent person.
Fire-resisting floors
The fire resistance of floors will depend on the existing floor construction as well as the type of ceiling finish beneath. If you need to upgrade the fire resistance of your floor it may not be desirable to apply additional fire resistance to the underside of an existing ornate ceiling. In older buildings there may be a requirement to provide fire resistance between beams and joists.
A typical example of a 30-minute fire-resisting timber floor is tongue and groove softwood of not less than 15mm finished thickness on 37mm timber joists, with a ceiling below of one layer of plasterboard to a thickness of 12.5mm with joints taped and filled and backed by supporting timber.
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There are other, equally valid, methods and products available for upgrading floors. If you are in any doubt you should ask the advice of a competent person and ensure that the product is installed in accordance with instructions from the manufacturer or supplier.
Fire resisting glazing
The most common type of fire-resisting glazing is 6mm Georgian wired glazing, which is easily identifiable. Clear fire-resisting glazing is available and can quickly be identified by a mark etched into the glass, usually in the corner of the glazed panel, to confirm its fire- resisting standard.
Although this is not compulsory, the marking of glass is supported by the Glass and Glazing Federation, you should check whether the glazing would be marked accordingly before purchase.
The glazing should have been installed in accordance with the manufacturer’s instructions and to the appropriate standard, to ensure that its fire-resisting properties are maintained. The performance of glazed systems in terms of fire resistance and external fire exposure should, wherever possible, be confirmed by test evidence. Alternatively, where there is a lack of test information, ask for an assessment of the proposed construction from suitably qualified people.
Fire separation of voids
A common problem encountered with fire separation is fire-resisting partitions, which do not extend above false ceilings to true ceiling height. This may result in unseen fire spread and a loss of vital protection to the escape routes. It is important therefore to carefully check all such partitions have been installed correctly.
CLASP and SCOLA type construction
CLASP (Consortium of Local Authorities Special Programme) and SCOLA (Second Consortium of Local Authorities) are total or systematic methods of construction that were developed to provide consistent building quality, while reducing the need for traditional skilled labour. They consist of a metal frame upon which structural panels are fixed. This results in hidden voids through which fire may spread.
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It is important that cavity barriers that restrict the spread of fire are installed appropriately, especially to walls and floors that need to be fire resisting. If you are in any doubt as to whether any remedial work will be required, then ask for advice from a competent person.
Breaching fire separation
To ensure effective protection against fire, walls and floors providing fire separation must form a complete barrier, with an equivalent level of fire resistance provided to any openings such as doors, ventilation ducts, pipe passages or refuse chutes.
The passing of services such as heating pipes or electrical cables through fire-resisting partitions leaves gaps through which fire and smoke may spread. This should be rectified by suitable fire stopping and there are many proprietary products available to suit particular types of construction. Competent contractors should install such products.
Décor and surface finishes of walls, ceilings and escape routes
The materials used to line walls and ceilings can contribute significantly to the spread of flame across their surface. Most materials that are used as surface linings will fall into one of three classes of surface spread of flame. The following are common examples of acceptable materials for various situations:
Class 0: Materials suitable for circulation spaces and escape routes
• Such materials include brickwork, block work, concrete, ceramic tiles, plaster finishes (including rendering on wood or metal lathes), wood-wool cement slabs and mineral fibre tiles or sheets with cement or resin binding.
Note: Additional finishes to these surfaces may be detrimental to the fire performance of the surface and if there is any doubt about this then consult the manufacturer of the finish.
Class 1: Materials suitable for use in all rooms but not on escape routes
• Such materials include all the Class 0 materials referred to above. Additionally, timber, hardboard, block-board, particle board, heavy flock wallpapers and thermosetting plastics will be suitable if flame-retardant treated to achieve a Class 1 standard.
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Class 3: Materials suitable for use in rooms of less than 30m2
• Such materials include all those referred to in Class 1, including those that have not been flame-retardant treated and certain dense timber or plywood and standard glass- reinforced polyesters.
Strong room construction:
This type of construction is adopted to protect important documents, wealth, currency notes from fire and thieves. Followings are important features of a strong room construction.
1.
2. 3.
The walls, floors and ceilings of strong room are constructed with minimum thickness of 30 mm.
Grills are to be placed in such a way that no gap is left.
Special precautions are to be exercising doors, windows, and ventilators of strong room.
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