Vessels responding to situations like that of Deepwater Horizon may encounter unexpected hazards with which they are unfamiliar and which are not immediately apparent.
A respondent on the gCaptain forum, Nomad, warns: “For any mariners responding to distress calls in circumstances such as this, it’s a good idea to stop – look – listen – before approaching too close. In this specific case, the venting hydrocarbons were ablaze, but in some cases there is no fire, just an uncontrolled flow. The presence of high concentrations of hydrogen sulfide gas is always a consideration, even with oil blowouts as there is often a gas component to the reservoir fluid.”
Hydrogen Sulphide, H2S, dangers are well known to offshore workers and vessels servicing them are usually equipped with H2S meters and alarms but others, such as fishing vessels will not. H2S is characterised by a ‘rotten eggs’ smell but the gas itself can disable the sense of smell in higher concentrations.
Says Nomad: “Sad stories exist – the Hasbah-6 blowout in the Persian Gulf back in the early ’80s, where much of the crew abandoned the platform for the sea only to be asphyxiated by H2S, which is heavier than air and settled on the water around them.
“If personnel can be seen moving, or are communicative, or the whole thing has gone cigarette lighter, you’re probably OK but a whiff of sulfide should be a strong warning. The bad part is that as the concentrations get higher, your ability to smell it diminishes. And air-breathing combustion devices stop working. Appropriate personal protective gear and good communication is necessary in such circumstances.
“(Also) If gas is rising to the surface at night when the boat can not see it, the gas will sink the boat.”