In order to prevent the premature collapse of the load-bearing structural elements of a building, appropriate levels of fire resistance duration (see annex 2.A) should be provided to all element of structure. The purpose of structural fire protection is:
to minimise the risk to the occupants, some of whom may not evacuate the building immediately, and
to reduce the risk to fire-fighters who may be engaged in fire-fighting or rescue operations.
An element of structure may perform more than one function and it is important that the appropriate guidance related to the different standards is followed.
An element of structure is part of a building which is part of a structural frame (beams and columns), load-bearing (other than part which is only self load-bearing), a floor, or supports a floor. An example of part of the structure that is only self load-bearing could be a lintel in a non load-bearing wall. A roof structure should not be considered as an element of structure unless the roof provides support to an element of structure or which performs the function of a floor.
It is essential that during a fire the elements of structure should continue to function. They should remain capable of supporting and retaining the fire protection to floors, escape routes and fire access routes, until all occupants have escaped, been assisted to escape or rescued by the fire and rescue service. In practice, the fire and rescue service could remain in the building long after it has been evacuated. For this reason, an additional level of protection is built into the guidance for domestic buildings that varies depending on the height of the topmost storey of the building.
Table 2.1. Protection of Structural Elements
|Height of topmost storey above ground level||Fire resistance duration|
|Not more than 7.5m||short|
|More than 7.5m but not more than 18m||medium|
|More than 18m but not more than 60m||long |
An intermediate floor or floors within a flat or maisonette need only have short fire resistance duration provided the floor or floors do not support or provide lateral restraint to any part of the structure with a medium or long fire resistance duration.
However the following element of structure need not be provided with any fire resistance for structural protection:
an element of structure in a single storey building which does not form part of, or provide support to, a separating wall, a wall or screen used to protect routes of escape (see clause 2.0.6) or an external wall which attracts a fire resistance (see guidance to Standard 2.6)
the lowest floor of a building.
An element of structure may be constructed from combustible material i.e. material which is low, medium, high or very high risk, (see annex 2.B) provided the element of structure has the appropriate fire resistance duration.
Where an element of structure provides support to another element of structure (or a protected route of escape, see clause 2.0.6) which should be constructed from non-combustible material, the supporting element of structure should also be constructed from materials which are non-combustible (see annex 2.B).
Where an element of structure provides support to another element of structure (or provides support to a protected route of escape) which attracts a higher period of fire resistance, the supporting element of structure should have at least the same period of fire resistance.
In general, openings and service penetrations in element of structure need not be protected from fire unless there is the possibility of structural failure. However where a large opening or a large number of small openings are formed, careful detailing particularly at the edge of the opening or service penetration should be carried out in order to maintain the load-bearing capacity of the element of structure. If in doubt, edge protection should be provided.
The detailing of junctions between relevant parts of a building is described in clauses 2.2.10, 2.4.7 and 2.9.21. Fire-stopping of other junctions is generally not necessary. The important criteria to consider is the ability of the element of structure to maintain its load-bearing capacity in a fire in accordance with clause 2.3.1.