Enclosed space entry checklist: gas limits, permit and rescue under IMO MSC.581(110)

• Test from outside the space, with ventilation stopped once conditions have stabilised — the IMO example permit suggests about 10 minutes.
• Test at different levels and through as many openings as you can; heavy gases sit low, light ones high.
• Restart ventilation after testing and keep it running, and keep testing while people are inside.

Source: IMO Res. MSC.581(110), revised recommendations for entering enclosed spaces aboard ships (paraphrased).

MSC.581(110) treats a space as enclosed when it may contain a dangerous atmosphere or too little oxygen and has any one of these: limited openings for entry and exit, poor ventilation, or it is not designed for people to work in all the time. On board that includes:

• Tanks and voids: cargo, slop, ballast, fuel, lube oil, fresh water and sewage tanks, cofferdams, duct keels, void spaces and pipe tunnels.
• Holds and trunks: cargo holds and access trunks, especially with cargoes that use up oxygen or give off gas (coal, timber, woodchips, grain, scrap, some fertilisers).
• Machinery and stores: boilers, crankcases and scavenge spaces, CO₂ rooms, chain lockers and unventilated store rooms.

1. Risk assessment and permit: a responsible officer completes the entry permit; check that no conflicting hot-work, cargo or ballast operation is planned nearby.
2. Isolate: close and lock or tag every valve and line into the space (cargo, ballast, steam, inert gas, CO₂) and isolate machinery inside.
3. Ventilate the space thoroughly.
4. Test the atmosphere to the limits above, record the readings and the time on the permit, then restart ventilation.
5. Rig rescue gear at the entrance before anyone enters: breathing apparatus, a lifting device and harness, lifelines, a stretcher, torches and first-aid and resuscitation equipment.
6. Post an attendant at the entrance for the whole job. The attendant never goes in to attempt a rescue alone.
7. Agree communications between entrant, attendant and the bridge or cargo control room, with regular check-ins. Never one person alone inside.
8. Monitor while inside: entrants carry personal gas monitors; leave at once on any alarm, if ventilation stops or if anyone feels unwell.
9. Close out: the permit should never be valid for more than 8 hours (MSC.581(110)). Count everyone and every tool out, secure the opening and sign the permit off.

Since 1 July 2016, SOLAS XI-1/7 (added by MSC.380(94)) requires every SOLAS ship to carry a portable atmosphere testing instrument that measures at least oxygen, flammable gas or vapour, H₂S and CO, and suitable means to calibrate it.

• Keep the calibration certificate, the calibration gas and its expiry date, and a log of every function check together — inspectors ask for all three. The Marshall Islands Marine Safety Advisory 12-26 (September 2026) is one recent warning about badly calibrated instruments.
• Use a sampling hose or pump long enough to reach the bottom of the deepest tank you enter.
• Know your alarm set-points; inspectors often ask the Chief Officer or Bosun to switch the meter on and explain them.

Crew with enclosed space entry or rescue duties take part in an enclosed space entry and rescue drill at least every two months (SOLAS III/19.3.3, from 1 January 2015). Vary the space — pump room, double-bottom manhole, hold ladder, forecastle store — so the team practises rigging the lifting gear at real openings. See all SOLAS drill intervals.