Page 73 - International safety guide for oil tankers and terminals
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HAZARDS OF PETROLEUM
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งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
Wind
approx
15 m
approx 8 m
Deck ึ
c) Total gas flow 46 cubic metres/minute. Approximate loading rate 2300 tonnes/hour.
The above illustration shows a vent riser 6 metres above the deck.
The plumes are based upon wind tunnel data of:
Gas mixture 50% by volume propane in the air
Diameter of opening 254 millimetres
Wind speed 1.1 metres/second
Figure 2.3 (c) – Indicative effect of gas flow rate on flammable zone
The flammable zones generated by the same operations with motor or
aviation gasolines would be similar but with a more pronounced density
effect, and this effect would be even more pronounced with a natural
gasoline type cargo. Also, the greater dilution required to reach the LFL
with motor or aviation gasolines (see Section 1.2.2) would tend to make
the flammable zones larger than with crude oils, and this effect would be
even more pronounced with the natural gasolines. Thus, the dispersion
problem becomes progressively more pronounced as one goes from
crude oils, through motor or aviation gasolines, to natural gasoline type
cargoes.
2.5.4.4 Concentration of Hydrocarbon Gas
With a constant total rate of flow of gas, changes in hydrocarbon
concentration have two effects. The rate of emission of hydrocarbon gas
increases in proportion to the concentration so that, other things being
equal, the extent of the flammable zone increases. Also, the initial density
© ICS/OCIMF/IAPH 2006 39