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Developed and maintained
by the NFCC

Hazard
Fires in chimneys

Hazard Knowledge

Whilst chimneys are purpose built elements of a structure designed to handle the removal of hot fire gases from within a structure there are many occasions where this system fails either due to poor maintenance, deterioration due to age or from new heating systems being built into pre-existing chimneys which are not fit for purpose.
 
Chimneys in older properties may not meet the required standard and beams or supports may intrude into the chimney. Chimneys may service several hearths, splitting over floors or across levels. This can allow fire or smoke to spread across levels unchecked. Poor states of repair or damage to a chimney may cause the structure to become unsound and allow products of combustion to escape. Fire service intervention should consider any planned actions and their potential effect on the chimney.
 
Rapid changes in temperature from the fire and from the cooling effects of water applied to the chimney may cause material to spall away or in the case of chimney pots, to break up with explosive effect, with the potential to cause injury to personnel working nearby or below.
 
The term ‘Blow Back’ is used to describe the high velocity steam escaping from the chimney which may cause significant injury to any personnel within the vicinity.
 
Domestic back boilers may also be a risk as any overheating caused by an uncontrolled chimney fire coupled with insufficient ventilation may cause the boiler to explode, possibly weakening the structure of the building and producing flying debris.
 
Access to a chimney fire can be particularly challenging both internally and externally.
 
See National Operational Guidance: Subsurface, height, structures and confined spaces