Fire safety (Means of scape,limit internal fire spread, limit external fire spread, provide access and facilities for the fire services )- Walls.

Tuesday, January 4, 2011

Fires in buildings generally start from a small source of ignition, the ‘outbreak of fire’, which leads to the ‘spread of fire’ followed by a steady state during which all combustible material burns steadily up to the final ‘decay stage’. It is in the early stages of a fire that there is most danger to the occupants of buildings from smoke and noxious fumes. The Building Regulations set standards for means of escape, limitation of spread of fire and containment of fire.
Fire safety regulations are concerned to assure a reasonablestandard of safety in case of fire. The application of the regulations, as set out in the practical guidance given in Approved Document B, is directed to the safe escape of people from buildings in case of fire rather than the protection of the building and its contents.
The requirements of Part B of Schedule I to the Building Regulations are concerned to:

(1) provide adequate means of escape
(2) limit internal fire spread (linings)
(3) limit internal fire spread (structure)
(4) limit external fire spread
(5) provide access and facilities for the fire services

Means of scape.
The requirements for means of escape from one and two storey houses are that each habitable room either opens directly on to a hallway or stair leading to the entrance, or that it has a window or door through which escape could be made and that means are provided for giving early warning in the case of fire. With increased height and size, where floors are more than 4.5 m above ground, it is necessary to protect internal stairways or provide alternative means of escape. Where windows and doors may be used as a means of escape their minimum size and the minimum and maximum height of window cills are defined.

Somoke alarms.
To ensure the minimum level of safety it is recommended that all new houses should be fitted with self-contained smoke alarms permanently wired to a separately fused circuit at the distribution board. Battery-operated alarms are not acceptable. Where more than one smoke alarm is fitted they should be interconnected so that the detection of smoke by any one unit operates in all of them.

Internal fire spread(linings).
Fire may spread within a building over the surface of materials that encourage spread of flame across their surfaces, when subject to intense radiant heat, and those which give off appreciable heat when burning.

In Approved Document B is a classification of the performance of linings relative to surface spread of flame over wall and ceiling linings and limitations in the use of thermoplastic materials used in rooflights and lighting diffusers.

Internal fire spread(structure).
The premature failure of the structural stability of a building during fires is restricted by specifying a minimum period of fire resistance for the elements of the structure. An element of structure is defined as part of a structural frame, a loadbearing wall and a floor.

The requirements are that the elements should resist collapse for a minimum period of time in which the occupants may escape in the event of fire. Periods of fire resistance vary from 30 minutes for dwelling houses with a top floor not more than 5 m above ground, to 120 minutes for an industrial building, without sprinklers, whose top floor is not more than 30 m above ground.

For information on the requirements for buildings other than dwellings, concerning purpose groups, compartments, concealed spaces, external fire spread and access for the Fire Services.

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