Bearing in mind the reduction of oxygen in ullage spaces
compounded by the operation of inert gas systems, research has led
to the conclusion that there is a significant risk of pyrophoric deposits
forming in inerted tankers carrying sour crude oil; furthermore, that
pyrophoric deposits can form with crude oils having a low hydrogen
sulphide content and that no minimum safe level of hydrogen sulphide
content can be identified; and, finally, that pyrophors which have
formed during a loaded passage can persist during the subsequent ballast
voyage.
Thus, while various factors (such as lack of sufficiently thick
deposits of iron oxide) may inhibit pyrophor formation and while the
correct operation of the inert gas plant will prevent the possibility
of ignition, the degree of risk is judged to be sufficiently high
to require the precautions in section 8.2 in
case of inert gas system failure.