of the bunker oil is below the flash point temperature. Clearly, in the second instance adequate vapour could be present in a bunker tank after a suitable period that could or would create a flammable mixture notwithstanding the fact that the flash point temperature is higher than the storage temperature.
Given the requirement in SOLAS (Part A – regulation 15) that a bunker oil should normally have a flash point temperature above 60oC, the situation and environment within the vessel’s settling and service tanks is somewhat different from those of the main bunker storage tanks. In general the temperature of the bunker oil within these two specified tanks is very much higher than the oil’s flash point temperature.
From the above description therefore it is to be expected that the vapour “head space” in both the settling and service tanks will contain adequate mixture combustible vapour and air such that with the presentation of an ignition source the vapour will “burn”. However, even at the elevated liquid temperatures the flash point temperature does not imply that the liquid volume will also ignite. As described above, for this situation to occur the liquid temperature must be above the laboratory simulated equivalent “fire point” temperature which is a temperature significantly above the flash point temperature.
What are the operational consequences of these observations?
Clearly above and around all bunker tank vents, particularly those for the settling and service tanks, no ignition source should be present – this should include smoking as well as “hot work” and welding on the poop deck in any currently defined safe area. If such is to be permitted then regular control and maintenance of flame screens within the vents should be undertaken and a hydrocarbon vapour check undertaken within the head space by use of hydrocarbon gas monitoring equipment.
Agenda for the CTC #32Page 37 of 39
To be held in Panama City on the 09 April 2008 Issue No. 1
Our Ref.: AGO-22713/1000003Approved by: H.N. Snaith