Introduction to Fire Safety Management

Table 7.3
Common commodities together with their 
known fi re loading
Commodity Heat 
release 
 MW/m
2
Wood pallets, stack 0.46 m high
1.4
(5–12% moisture)
Wood pallets, stack 1.5 m
5.2
high (5–12% moisture)
Wood pallets, stack 3.1 m high
10.6
(5–12% moisture)
Polyethylene rubbish litter bins in
2
cartons, stacked 4.6 m high
Polystyrene jars packed in cartons,
14
compartmented, stacked 1.5 m high
Polystyrene tubs nested in cartons,
5.4
stacked 4.3 m high
20–25 video cassettes 
1 

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Principles of fi re and explosion
127
7.5
Explosion
As the terminology surrounding explosion is generally 
less familiar than that of fi re, it is benefi cial to defi ne 
certain terms to clarify future explanations.
7.5.1 Terminology
Explosion
– an abrupt oxidation, or decomposition reac-
tion, that produces an increase in temperature, or pres-
sure, or in both temperature and pressure simultaneously.
Explosive atmosphere
– fl ammable substances in the 
form of gases, vapours, mists or dusts mixed with air 
under atmospheric conditions, which, after ignition has 
occurred, combustion spreads to the entire unburned 
mixture.
Defl agration
– a combustion wave propagating from an 
explosion at subsonic velocity relative to the unburnt gas 
immediately ahead of the fl ame (fl ame front).
Detonation
– a combustion wave propagating from an 
explosion at supersonic velocity relative to the unburnt 
gas immediately ahead of the fl ame (fl ame front).
BLEVE – boiling liquid expanding vapour explosion
– 
an explosion due to the fl ashing of liquids when a vessel 
with a high vapour pressure substance fails.