CDOIF Guidance

Safety and environmental standards for fuel storage sites

Final report

5 An initial review of commonly stored liquids using the methodology indicates that the following

substances have the potential to give rise to a large vapour cloud in the event of an overfill:

acetone;

■

benzene;

■

natural gas liquids (condensates);

■

iso pentane;

■

methyl ethyl ketone;

■

methyl tert-butyl ether;

■

naphthas;

■

raw gasoline;

■

reformate (light);

■

special boiling point 2;

■

toluene.

■

6 Further work has shown that the methodology can be further refined for substances that

appear to be borderline by consideration of the Reid vapour pressure (RVP), composition and

heat of vaporisation. This system is summarised below:

Use Reid vapour pressure for single component liquids not listed in paragraph 5. Single

■

component liquids with RVP

≥

2.5 should be considered as capable of giving rise to a large

vapour cloud.

For multi-component mixtures the tank filing rate and tank size should be considered. For

■

these liquids including crude oils, mixtures with RVP

≥

2.5 and meeting the following condition

should also be considered as giving rise to a large vapour cloud:

Filling rate (m

––

/hr) x liquid density (kg/m

)/tank perimeter (m) >3600. Note: a default density

of 750 kg/m

could be used.

This indicates that crude oils (meeting the criteria outlined in paragraph 6) and toluene

––

also have the potential to form a large vapour cloud in the event of an overfill. For toluene,

the cloud concentration at the base of a tank has been shown by research to be just

above its lower flammable limit. However, there is a degree of uncertainty over whether

its subsequent movement and dilution would lead to the formation of a large flammable

vapour cloud. Taking a precautionary approach it would seem sensible to consider that it

would.

7 In conclusion Table 6 shows the outcome of the application of the methodology in Part 1

and the refinement using Reid vapour pressure, as set out in paragraph 6, to commonly

stored liquids. Note that the conditions which apply to these other substances in order to be

considered likely to form a large vapour cloud, are as defined for gasoline in paragraph 24 of the

main report.