The spread of fire can be restricted by sub-dividing buildings into a number of discrete compartments. These fire compartments are separated from one another by compartment walls and compartment floors made of a fire-resisting construction which hinders the spread of fire from one compartment to another.
The fire resistance of an element of construction is a measure of its:
Resistance to collapse.
Resistance to fire penetration.
Resistance to the transfer of excessive heat.
Care must be taken to ensure that junctions between fire-resisting elements and openings between them do not create a weakness.
Approved document B, Fire Safety, defines a fire stop as: ‘A seal provided to close an imperfection of fit or design tolerance between elements or components, to restrict the passage of fire and smoke.‘
It goes on to state, ‘if a fire-separating element is to be effective, then every joint, or imperfection of fit, or opening to allow services to pass through the element, should be adequately protected by sealing or fire-stopping so that the fire resistance of the element is not impaired.’
Joints between fire-separating elements such as compartment walls or floors, should be fire-stopped to maintain the continuity of resistance; and openings for timber beams, joists, purlins and rafters, and pipes, ducts, conduits or cables that pass through any part of a fire-separating element should be kept as few in number as possible, kept as small as practicable, and fire-stopped.
Fire-stopping materials include:
Cement-based or gypsum-based vermiculite/perlite mixes.
Glass fibre, crushed rock, blast furnace slag or ceramic-based products (with or without resin binders).
Proprietary fire-stopping and sealing systems.
In the case of a pipes or ducts, fire stopping should allow thermal movement.
Where an unsupported span is greater than 100 mm or where non-rigid materials are used (unless they have been shown to be satisfactory by test), materials used for fire-stopping should be reinforced with, or supported by, materials of limited combustibility.
Effective fire-stopping requires good awareness of technical literature and standards, and effective inspection of works on site. This is particularly important where fire-stopping may be left to the end of the construction process, installed by a subcontractor, or where it is concealed. The integrity of fire stopping must then be maintained through repairs and refurbishment works.
NB: Fire dampers are installed in the ducts of heating, ventilation and air conditioning systems which penetrate fire-resistant constructions and will automatically close on the detection of heat.