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INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

compatible with the definitions adopted internationally by IMO and by a number
of regulatory bodies throughout the world. (See Section 2.7 for information on
2.5ศึกษาเท่านั้น---
the relationship between the flashpoint and flammability of residual fuel oils.)

งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
1.3 Density of Hydrocarbon Gases

The densities of the gas mixtures evolved from the normal petroleum liquids, when
undiluted with air, are all greater than the density of air. Layering effects are therefore
encountered in cargo handling operations and can give rise to hazardous situations.

Table 1.2 gives gas densities relative to air for the three pure hydrocarbon gases,
propane, butane and pentane, which represent roughly the gas mixtures that are
produced respectively by crude oils, by motor or aviation gasolines and by natural
gasolines. These figures are not significantly changed if inert gas is substituted for air.

Density relative to air

Gas 50% by volume
Pure Lower flammable
hydrocarbon/
hydrocarbon limit mixture
50% by volume air
---ใช้เพื่อการ
Propane 1.55 1.25 1.0
ึ
Butane 2.0 1.5 1.0
Pentane 1.8 1.0

Table 1.2 – Propane, butane and pentane: densities relative to air

It will be seen that the density of the undiluted gas from a product such as motor
gasoline is likely to be about twice that of air, and that from a typical crude oil about
1.5 times. These high densities, and the layering effects that result from them, are only
significant while the gas remains concentrated. As it is diluted with air, the density of the
gas/air mixture from all three types of cargo approaches that of air and, at the Lower
Flammable Limit, is indistinguishable from it.

8 © ICS/OCIMF/IAPH 2006