Introduction to Fire Safety Management

Figure 8.21
Internal fl ammable storage facility

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Causes and prevention of fi re
155
Ventilation of storage areas
Ventilation has been discussed as part of the storage 
requirements; however, all areas where fl ammable liquids 
are handled should be adequately ventilated to ensure 
that any released vapours are diluted to a safe level.
Whichever ventilation system is used it needs to 
be capable of providing a minimum of six complete 
air changes per hour. The system’s capacity should 
ensure that the amount of vapour in the atmosphere is 
not only diluted to well below its fl ammable limit, but 
also reduced to a level below any relevant workplace 
exposure limit (HSE’s guidance note EH 40 gives advice 
on workplace exposure limits).
Dependent upon the concentrations and volumes 
in use good, natural, well-positioned ventilation may be 
adequate, but where this cannot be achieved, mechan-
ical ventilation and/or local exhaust ventilation (LEV) is 
almost certain to be needed.
Positive pressure mechanical systems can be 
used to force air into an area; diluting and venting any 
potential build-up of fl 
ammable vapours. Any area 
provided with a positive pressure mechanical system 
will also need to be provided with suffi cient openings 
to release the atmosphere created. LEV systems are 
designed to capture airborne contaminants such as 
fl ammable vapours, fi lter them and ventilate outside a 
building to a place of safety in the open air.
Any vents provided for the release of pressure or 
contaminants should be a minimum of 3 m above ground 
level, at least 3 m from building openings, boundaries 
and sources of ignition, and away from building eaves 
and other obstructions where they could become 
trapped. The ducting taking the fl ammable vapours 
away should be arranged so that they cannot condense 
and collect at low points within them.