Question 1

Before entry into a double-bottom tank, the bosun tests the atmosphere at the access hatch — O₂ 20.7%, all gas readings clear. He says there is no need to test lower in the tank because "it's the same air all the way down."

Is he correct?

Accepted Answer

No. Heavier-than-air gases (CO₂, H₂S) stratify and accumulate at the lowest points of any enclosed space. The reading at the hatch can be completely normal while a lethal layer exists at the bottom of the tank Gas stratification is a fundamental physical property, not a tanker-specific concern. CO₂ (SG 1.52) and H₂S (SG 1.19) are both heavier than air. Even after ventilation, pockets of heavy gas can persist in low sections of double-bottom tanks, bilge wells, and corrugated floor sections — invisible to a reading taken at the top. COSWP requires testing at all levels before entry, including at the furthest point from the ventilation inlet.

Question 2

The bosun approaches you — the duty officer — and says he needs to "pop into the pump room for two minutes" to check the bilge level. The gas meter is on charge. No permit has been raised. He says he knows the space well and has done this dozens of times.

What is your response?

Accepted Answer

Stop him. No entry is permitted without a valid atmosphere test and an authorised Enclosed Space Entry permit, regardless of familiarity with the space or duration of entry Familiarity and brevity are the two most lethal attitudes in enclosed space entry. The pump room atmosphere can change in seconds from an undetected gas source. A permit and atmosphere test are mandatory before any entry — COSWP Ch.17 and SOLAS XI-1/7 make no exception for "quick checks". The majority of ESE fatalities involve spaces the victim entered regularly without incident.

Question 3

Pre-entry atmosphere test at the manhole opening of a cargo hold: O₂ 20.5%, LEL 0%, H₂S 0 ppm, CO 0 ppm. The bosun says "It's fine — readings are all in range, let's go in." The hold contained a grain cargo and has been empty for 18 days.

What additional step is essential before entry proceeds?

Accepted Answer

The atmosphere must also be tested at lower levels within the space — at working depth and at the bottom. A safe reading at the entry point does not guarantee safe conditions deeper in the hold Gases heavier than air (CO₂, H₂S) pool at the bottom of cargo holds. Grain cargo self-heats and consumes O₂ through biological activity — the dangerous zone may be the bottom metre of an apparently safe space. COSWP requires testing at multiple levels, especially in spaces with a known biological or chemical cargo history. Testing only at the hatch is a common precursor to fatalities.