Hazard Impact of fire or firefighting on structural elements or structural frames
Knowledge and understanding
|Impact of fire or firefighting on structural elements or structural frames||
Understand all associated hazard knowledge
Structural elements and structural frames may be affected by fire, or by firefighting. For knowledge about this hazard, refer to the sections in the BRE supplementary information about structural elements and structural frames.
Structural elements will have varying behaviours when their integrity is affected by fire, including:
- Air-supported structures are prone to early collapse if fire burns through the membrane, resulting in a drop of air pressure
- Arches may fail rapidly, depending on their construction method and materials
- Beams may fail, resulting in collapse of the load they are supporting
- Columns are load bearing and failure is likely to result in the collapse of other structural elements, including other columns
- Connections may fail prematurely during heating or cooling, with failures leading to partial or structural collapse being more likely during cooling
- Floors involved in fire should be investigated for stability; their collapse can lead to collapse of other structural elements
- Load bearing walls involved in fire should be investigated for structural integrity; modern walls may be built around timber frames and if fire has penetrated the cladding a more serious failure may occur due to undetected firespread
- Lintel failure may lead to localised collapse of walls above an opening, or entire walls if the lintel is over a large opening
- Trusses may fail if involved in fire, singularly or as a whole system, leading to collapse of lightweight or fragile building features, or even to load bearing walls
Structural frames and their behaviour in fire include:
- Temporary or demountable structures that have the potential for rapid structural failure
- Masonry integrity that is dependent on the quality of workmanship; failure of masonry can impact on the structural element it forms, such as arches, beams and columns. This is also affected by mortar quality and integrity; it can crumble in later stages of fire, or after fire, impacting on the integrity of masonry or blockwork.
- Individual modules, which are usually robust and should have undergone quality control and testing (including fire testing) as a completed unit. Weaknesses in a modular structure are usually found in how they are joined to other modules.
- Portal or rigid frame buildings that have the potential for rapid structural failure, with inward collapse
- Steel frames that will lose strength and stiffness at relatively low temperatures (over 550°C) in relation to compartment fire development, causing deformation and possible collapse
- Timber frames that may be difficult to identify as they are not usually exposed; there may be hidden firespread behind the outer skin of the building. Without fire protection, timber frame buildings under construction present a high risk of rapid firespread and early collapse.