Question 1

Why is hydrogen sulphide (H2S) specifically tested for in spaces that have contained sewage, ballast water with biological growth, or certain cargo residues?

Accepted Answer

H2S is highly toxic even at low concentrations, is heavier than air so it pools at low points, and can rapidly deaden the sense of smell, removing the natural warning cue H2S is acutely toxic at low ppm levels and is heavier than air, accumulating in bilges, sumps, and low points. Critically, at higher concentrations it causes rapid olfactory fatigue ("nose blindness") — the rotten-egg smell that initially warns of its presence can disappear even as the concentration rises, removing a sense of false reassurance just as the danger increases.

Question 2

Under MSC.581(110), what is the maximum acceptable CO2 reading (by volume) before an enclosed space can be considered safe for entry?

Accepted Answer

Less than 0.5% by volume (5,000 ppm) Para. 7.4 sets the CO2 exposure limit at below 0.5% by volume (5,000 ppm) before entry; if this is not achieved, the space remains unsafe. CO2 is now explicitly addressed as a major asphyxiation hazard alongside oxygen depletion.

Question 3

Under the revised recommendations, is single-person entry into an enclosed space ever permitted?

Accepted Answer

No — the company must ensure single-person entry into an enclosed space is not permitted Para. 3.11 explicitly prohibits single-person entry into an enclosed space under any circumstances covered by the recommendation.