Gas detectors for enclosed space entry: SOLAS XI-1/7, calibration and bump tests

Why it matters

Between 2000 and 2024 at least 1,010 people died in enclosed spaces on ships, about 50 a year in recent years, and most of them were crew. On the Berge Mawson in 2022 three stevedores died in a hold where the ship’s calibrated detector had shown 5.8 % oxygen that same morning; nobody tested again before they went in.

What SOLAS requires

SOLAS regulation XI-1/7, added by Resolution MSC.380(94) and in force since 1 July 2016, requires ships to carry an appropriate portable atmosphere testing instrument, or instruments, able to measure at least:

• oxygen,
• flammable gases or vapours,
• hydrogen sulphide,
• carbon monoxide,

before anyone enters an enclosed space. Instruments already carried under other rules may count, and suitable means must be provided to calibrate them. Flags read the scope differently: Lloyd’s Register applies it to all SOLAS-certified ships, while the Isle of Man applies it to passenger ships of any size and other ships of 500 GT and above.

What a suitable instrument looks like

MSC.1/Circ.1477 is a guide for choosing instruments, not a performance standard, and it does not cover the small personal detectors worn by each person. It asks for:

• a sampling pump and hose to measure remotely, and a self-test;
• a display for each of the four gases;
• alarm levels as set by the flag;
• intrinsic safety and at least 10 hours of battery life;
• users trained in its use, and calibration as the maker defines;
• a lockout when calibration is overdue that does not switch the instrument off during use but stops it being restarted.

Calibration and bump tests

SOLAS sets no calibration interval. MSC.1/Circ.1561 confirms that calibration may be done on board or ashore, as long as it follows the maker’s instructions. In practice the makers set the pace:

Maker and instrument	Calibration	Bump test
Dräger X-am 2800/5800	Every 6 months (4 months for the catalytic sensor on hydrogen); 12 months only with an advanced bump test before every use	Before each use
MSA ALTAIR 4XR	At least every 6 months	Before each day’s use
Honeywell portable detectors	Every 30 to 180 days	Before each day’s use

If a bump test fails, the instrument is calibrated before it is used again, or taken out of service. Calibration gas has a shelf life, for example 24 months for a common four-gas mix; never use it after the expiry date. Sensors wear out too: there is no IMO limit, but makers’ warranties run from one to four years depending on the sensor.

No IMO rule asks for a bump test log, but makers and OSHA recommend keeping one, and it is the simplest way to show an inspector that the instruments are checked.

What the 2025 recommendations add

Resolution MSC.581(110), adopted on 27 June 2025, replaces the 2011 recommendations for entering enclosed spaces (A.1050(27)). It is a recommendation, not a mandatory rule, but it is the current IMO guidance on safe entry. Among the changes:

• an Enclosed Space Register and new definitions of connected and adjacent spaces;
• the person in charge of entry at management level;
• an oxygen entry criterion of 20.9 % (was 21 %) and a new carbon dioxide limit below 0.5 %;
• testing at several levels and locations, with instruments that work in oxygen-depleted air;
• at least two sets of gas detection equipment, and personal detectors that also read carbon dioxide and flammable gas;
• no single-person entry, and recorded training, including in calibration.

The resolution speaks of “two sets as required by XI-1/7”, while SOLAS XI-1/7 itself only says “instrument or instruments”, so check what your flag expects.

Drills and inspections

Since 1 January 2015, SOLAS III/19 requires enclosed space entry and rescue drills at least every two months, including the checking and use of the atmosphere testing instruments, recorded in the log-book. PSC may ask for the records and a demonstration. In the 2015 concentrated inspection campaign, Tokyo MoU inspectors found no means of testing the atmosphere in 174 of 6,826 inspections, and 7.1 % of the drills they observed failed the requirement.

Checklist

1. Check each instrument against MSC.1/Circ.1477, and add carbon dioxide and any cargo-specific gases.
2. Decide who calibrates: trained crew on board, a shore laboratory, or rotating instruments, and keep a certificate for each serial number.
3. Bump test before use, and take a failing instrument out of service until it is calibrated.
4. Track the expiry date and certificate of every calibration gas cylinder.
5. Test at several levels, record the readings on the permit, and test again after breaks.
6. Give everyone who enters a calibrated personal detector.
7. Keep drill, calibration, service and training records ready for PSC.

How we help

We calibrate portable and fixed detectors with traceable gas, replace sensors before they fail, supply calibration gas with its certificates, and track every serial number’s due date in your customer portal. See Gas detection and calibration.