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Hazard
Partial or structural collapse: Fires in buildings

Hazard Knowledge

In a fire elements of building construction may distort or fail at different temperatures and speeds, depending on how the various construction materials have been used or combined. This can mean varying stages and severity of collapse.

Lightweight or fragile building features may collapse, including non-structural elements; such as conservatories, felt covered roofs, glazing and false chimneys.

False chimneys do not form part of the structural fabric of the building and may only be supported by roof timbers. False chimney may be made of glass-reinforced plastic (GRP) or in some cases, especially in conservation areas, they may be constructed from heavy masonry.

If the roof has a false chimney and the supporting roofing timbers or lightweight trusses are damaged by fire or collapse, the false chimney may fall through the roof joists or off the roof to the ground.

Elements of structure, floors, walls, ceilings, ancillary items, fixtures and fittings can partially collapse. Partial collapse can follow on from the collapse of lightweight or decorative features.

Partial collapse may expose structural elements to fire and heat which, if not controlled, will increase the potential for structural collapse.

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Structural collapse of building - photograph courtesy of the Building Research Establishment

Structural fire resistance should maintain the stability of a structure for a period, during which evacuation and firefighting can be carried out. However, missing or damaged fire protection may lead to premature structural failure.

Firefighting activity may have an adverse effect on the structural stability of a building. Damage can occur to structural fire protection during firefighting activities; rapid heating and then cooling by firefighting water can result in a loss of strength in the structural elements.

The load increases if firefighting water is being held within the structure, which may result in collapse.

Cutting structural elements during firefighting operations, for example to carry out ventilation, can also have an impact on the structural stability of a building.