OCIMF has issued a warning over increasing levels of H2S in some crude oils, encouraging tanker and terminal operators to remain alert to the dangers posed by the presence of H2S within cargoes or residues from previous cargoes.

While the dangers relating to Hydrogen Sulphide (H2S) are not new there is a growing body of evidence suggesting that H2S levels in some crude oils is on the increase. The reason for this apparent increase is unclear.

H2S is known to be present in crude oil exported from a number of countries including Iran, Qatar, South America, Mexico, Poland, Latvia, Russia and Turkey. Recently higher than normal amounts have been detected in Brent crude and within the last few days very significant amounts of H2S have been found in the ullage spaces of two tankers loading fuel oil cargo at Jubail in the Arabian Gulf.

Terminal operators should remain alert to the dangers posed by the presence of H2S, either within cargoes being delivered or remaining within the residues from a previous cargo. The precautions and procedures described within ISGOTT should be strictly adhered to.

The advent of Inert Gas and Closed Loading systems has largely negated the need to open tanks except for non-routine purposes, although reducing tank pressures to near zero for sampling is a relatively common practice. Purging for cargo preparation is also common, thus the planned release of the entire tank atmosphere, particularly where unexpectedly high levels of H2S are involved, poses a significant danger to individuals in the immediate and, in some cases, the not so immediate, area.

Some countries, particularly in Europe, have already stipulated maximum H2S levels in tanks prior to loading and some terminal operators have reduced their acceptable arrival levels from 10ppm to 5ppm.

In view of the above, we believe that it is sensible to encourage all crude vessels to monitor tank atmospheres and to advise of H2S levels in order that terminal operators may gauge the magnitude of what is clearly a growing problem. In addition, it may be prudent to encourage the monitoring of fuel oil vessels from areas which historically are known to pose a problem, such as, Jubail.

Regarding measurement, please be aware that while Draeger type tubes provide an accurate indication of H2S levels regardless of whether the tank atmosphere is inerted or not, H2S readings taken with an electronic meter in an inerted atmosphere do not.

Readers are asked to take note of the above and to advise operational staff, surveyors and other relevant personnel accordingly.

Source: Oil Companies International Marine Forum