Knowledge and understanding
Understand all associated hazard knowledge
Concealed spaces in a building's construction may provide a route for fire to develop and spread undetected.
Fire and smoke may spread to other areas of the building, possibly at some distance away from the seat of the fire.
Firespread in building voids and cavities may advance through openings to other parts of the building, including internal or external walls, and roofs.
Concealed spaces include:
- External wall cavities
- False or suspended ceilings
- Between modules in a modular construction
- Roof spaces
- Chimneys and flues
- Utility ducting
- Space under floors
- Space behind cladding
- Within sandwich panels
- Within structural insulated panels (SIPs)
It may be difficult to identify the structural elements and materials of the building if they are hidden behind facades and cladding.
Combustible insulation used in wall cavities and insulated panels can contribute to undetected firespread. Fire involving the combustible core of sandwich panels and structural insulated panels (SIPs) may result in elements of the panel failing, potentially leading to partial or structural collapse. Combustible sandwich panels may cause dense, corrosive and toxic smoke. It is important to consider that a single building may feature more than one type of sandwich panel.[BH1]
Debris may fall when concealed spaces are accessed. Concealed spaces may contain hazardous materials such as asbestos.
Window frames constructed from timber or steel will usually resist firespread into the wall cavity if they have been fitted correctly. However, aluminium and unplasticized chloride (uPVC) frames require specific cavity closers to prevent firespread into the wall cavity. Fire may spread into wall cavities via incorrectly fitted, or damaged, door or window frames.
Building modifications could provide concealed spaces, for example:
- Construction or removal of partition walls
- Addition or removal of doors
- Installation of electrical or mechanical machinery or systems
- Retro-fitting of façade assemblies and cladding
Ventilation can increase the speed of development of undetected firespread. See hazard Uncontrolled ventilation for more information.