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Hazard Knowledge

Cables may present hazards including:

  • Electrocution
  • Entanglement
  • Hazardous products of combustion

Cabling may become unsecured for two main reasons: 

  • Heat, potentially due to fire 
  • Partial or structural collapse of a building 

Cabling, including electrical and data cables, is used extensively in buildings; some cabling relies on surface mounted conduit and trunking. 

Electrical upgrades and retrofitted electrical sockets, light fittings, security or fire alarms and data cables means that lightweight cable fixings may be present in older buildings. Cabling may be concealed above suspended ceilings, with little or no fixing; those suspended ceilings may distort or fail at relatively low temperatures. 

Plastic conduit or trunking that is surface mounted on ceilings and walls will fail at relatively low temperatures of around 100oC. Aluminium trunking may also fail due to heat.  

If a suspended ceiling, conduit or trunking fails, cables may be released, potentially at some distance from the seat of fire. As a result, cables may present a risk of entanglement or electrocution to personnel. 

From 1 January 2016, regulations require that all new wiring systems use metal, rather than plastic, to support cables in escape routes, to prevent their premature collapse in a fire. Electrical installations fitted before changes to the regulations, or that do not conform to the regulations, may still present a hazard.

Cables dislodged from suspended ceiling fixings following a fire in compartment – photograph courtesy of Brian Massie

Most cables are sheathed or protected with polyvinyl chloride (PVC), polyethylene (PE) or thermoplastic polyurethane (TPU). In a fire, these plastics release dioxins, hydrogen cyanide and hydrogen chloride. See National Operational Guidance: Fires and firefighting – Smoke and fire gases