Where this sits
Governing: SI 2022/96 (Entry into Enclosed Spaces) Regulations; MGN 659 (M+F) Amendment 3; COSWP 2026, Chapter 15. Builds on: L2.1.
What counts
COSWP 15.1.1, following SI 2022/96, defines an enclosed space as one not designed for continuous worker occupancy with limited openings for entry and exit, inadequate ventilation, or both. The atmosphere may at any stage be toxic, flammable or short of oxygen, and the danger is usually invisible.
COSWP 15.1.7 lists examples. On a yacht, the ones you will actually meet are:
- chain lockers;
- void spaces and cofferdams;
- fuel tanks and double bottoms;
- sewage (black water) tanks;
- CO2 rooms;
- battery lockers;
- engine crankcases;
- any space adjacent or connected to one of the above.
Spaces can change. A lazarette being spray-painted, or a locker next to a leaking tank, can become an enclosed space for a while (15.1.3, 15.1.8). A register of enclosed spaces should be kept, and if in doubt, treat the space as enclosed until the atmosphere has been tested.
Why it kills
WARNING: One breath COSWP 15.1.4: "A single inhalation with a 5% oxygen content may result in instantaneous loss of consciousness and subsequent death." You will not feel short of breath first. You will simply fall.
Normal air holds about 20.8% oxygen. COSWP requires a steady reading of at least 20% by volume before entry. Rust, drying paint, sewage and inert gas all consume oxygen or displace it. Sewage tanks can also hold hydrogen sulphide, which deadens your sense of smell.
Safe entry, in outline
- Risk assessment by a competent person.
- Permit to work issued by an authorised officer.
- Isolate and secure the space (pipework, pumps, electrics).
- Ventilate, then test the atmosphere from outside, top, middle and bottom.
- Standby person at the entrance with communications and a means of raising the alarm.
- Rescue equipment and breathing apparatus ready at the entrance before anyone enters.
- Test again at intervals set by the risk assessment while people are inside.
If the atmosphere is suspect, entry is only for essential safety-of-life or ship reasons, or for testing, and always with breathing apparatus.
Drills
Enclosed space entry and rescue drills must be held at intervals not exceeding two months and recorded in the official log book (MGN 659). The 2026 COSWP revisions to Chapter 4 followed MAIB findings on rescues when shore staff were present, for example contractors in a yard. Make sure refit contractors know the yacht's enclosed spaces and rescue arrangements.
CAUTION: The rescuer is the second casualty In many enclosed space deaths the second person in was trying to help. Raise the alarm. Do not enter without breathing apparatus, a standby person and a plan.
Yacht notes
- Tender garages and toy stores with petrol, and lockers with lithium batteries, need assessment even if they are not on the register.
- Bow thruster rooms and anchor wells are often forgotten.
- Ask the chief officer where the gas detector is kept and when it was last calibrated.