Start hereRules checked 20 October 2026
A gas detector drifts. Sensors age, get poisoned by silicone sprays or exhaust, dry out in heat or get wet. The display still shows a confident number. The only ways to know whether that number is true are to expose the sensors to a gas of known strength (a bump test or calibration check), and to adjust them when they are off (a calibration).
SOLAS has required “suitable means” for calibrating every ship’s portable atmosphere testing instrument since 1 July 2016, and the IMO has had to explain twice (once for this meter, once for the tanker instruments of SOLAS II-2/4.5.7.1) that a quick test with span gas before use is not what the rule means. Calibration is also where port state inspectors look first: an out-of-date certificate is easy to spot, and the Marshall Islands Administrator has warned owners about a rise in US Coast Guard deficiencies for poorly calibrated instruments.9
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In this lesson
- Gas detection locker check before a port state inspection
- In plain words
- In detail
- What the rules say
- Flag and class notes
- Key numbers
- What inspectors find
- Quiz: 6 questions
Try it
Gas detection locker check before a port state inspection
In plain words
There are three different checks, and people mix them up:
- Bump test. Spray a known gas over the sensors and watch them respond and the alarms go off. It answers one question: does it work? It takes a minute. It does not change anything inside the meter.7
- Calibration check. The same, but you compare the reading with the gas strength printed on the cylinder. It answers: is it accurate enough?7
- Full calibration. The meter is adjusted, on board by a trained person or ashore by a service provider, so that it reads correctly again. It answers: make it accurate. It ends with a calibration certificate.7
The SOLAS rule is about the last one. The IMO says that calibrating on board or ashore, following the maker’s instructions, meets the rule, and that the pre-use “accuracy test” is something else.2 So a ship needs both: span gas and know-how for the daily bump test, and a plan for regular calibration with paperwork to prove it.
In detail
What the rules require
SOLAS regulation XI-1/7 ends with one sentence: “Suitable means shall be provided for the calibration of all such instruments.”1 The Maritime Safety Committee interpreted it in MSC.1/Circ.1561 (28 November 2016): compliance “may be achieved by portable atmosphere testing instruments being calibrated on board or ashore in accordance with the manufacturer’s instructions”. The circular adds that this refers to calibration, “and not to any pre-operational accuracy tests as recommended by the manufacturer”.2 MSC.1/Circ.1581 (16 June 2017) gives exactly the same interpretation for the tanker instruments required by SOLAS II-2/4.5.7.1.6
MSC.1/Circ.1477 adds that the maker’s instructions should clearly define the calibration requirements, and that a calibration over-due alarm should not stop the instrument working during actual use.8 MSC.581(110) asks for “certified and calibrated instruments” for the pre-entry test, and for personal detectors to be “calibrated and tested”.4
Fixed systems have the same principle. The IGC Code requires gas detection equipment to be readily tested, with testing and calibration at regular intervals, suitable equipment carried on board and permanent connections for it.10 The FSS Code chapter 16 requires fixed hydrocarbon gas detection on oil tankers to be designed so that it may readily be tested and calibrated (lesson 4).11
The three checks compared
The definitions below follow the industry statement on validating direct-reading portable gas monitors published by the International Safety Equipment Association (ISEA) in 2010, as summarised by a major maker. They are good practice, not IMO rules; your maker’s manual decides the details for your instrument.7
| Bump test | Calibration check | Full calibration | |
|---|---|---|---|
| Purpose | Sensors respond and alarms activate | Reading within tolerance of a known gas | Adjust readings to a known gas |
| Gas | Test (span) gas strong enough to trigger alarms | Known, traceable concentration | Known, traceable concentration |
| Changes the instrument? | No | No | Yes |
| Typical frequency (practice) | Before each day’s use | Before each day’s use, as alternative to bump | Maker’s interval, and after a failed check |
| Typical tolerance (practice) | Alarms activate | about ±10 to 20% of the test gas, unless the maker says otherwise | To the maker’s specification |
| Who | Trained crew | Trained crew | Trained crew with maker’s procedure and equipment, or service provider ashore |
| Record | Bump test log | Log | Calibration certificate |
The same summary advises a full calibration after a failed bump test, and taking the unit out of service if it fails again.7
Doing a bump test properly (practice)
- Switch on in clean air, away from engine exhaust and paint stores, and let the self-test and zero finish.
- Check the span gas: correct mix for your sensors, in date, cylinder pressure, the regulator flow the manual asks for.
- Fit the calibration cap or hose and apply the gas for the time the manual states.
- Every sensor must respond and every alarm (audible, visual, vibration) must activate. On a calibration check, readings must be within the maker’s tolerance.
- Purge with clean air and let the readings return to normal.
- Log it: date, time, instrument serial, gas lot and expiry, result, initials. Many instruments and docking stations record this automatically.
- Fail? Do not use it. Calibrate it, or use the spare and send it ashore.
Watch the sensor poisons and inhibitors that makers warn about: silicone sprays and sealants, lead compounds and high H₂S can damage catalytic sensors, and a sensor that has seen a very high concentration should be checked before it is trusted again.
Calibration on board or ashore
Both are accepted.2 Each has consequences:
| On board | Ashore | |
|---|---|---|
| Needs | Maker’s calibration kit, correct calibration gas, trained crew, written procedure in the SMS | Service provider, shipping time, a spare instrument |
| Evidence | Calibration record or printout from the instrument or docking station | Calibration certificate from the provider |
| Flag points to check | Marshall Islands: crew trained, calibration means as specified by the maker on board, SMS covers calibration, testing and use9 | Bahamas: alternative instrument on board while one is ashore; certificate with the in-use instrument5 |
Reading a calibration certificate
A useful certificate lets an inspector match it to the meter in their hand. Check that it shows:
- instrument make, model and serial number, and the serial or channel of each sensor;
- date of calibration and the date next due (or the interval used);
- each gas: test gas concentration, reading before adjustment (“as found”), reading after adjustment (“as left”), and pass or fail;
- alarm set points as left (remember that alarm levels are set by the flag Administration where it specifies them8);
- calibration gas identity, lot number and expiry, and traceability;
- who did it, where, and their signature.
“As found” readings tell you how far the instrument drifted since the last calibration; a large drift is a reason to shorten the interval.
When the interval is not obvious
Neither SOLAS nor the IMO guidelines set a calibration interval. It comes from the manufacturer’s instructions,28 sometimes tightened by the flag, the company or a charterer. Common sense says calibrate sooner after a failed bump test, exposure to high gas concentrations or poisons, a sensor change, or a long period unused.
What the rules say
- SOLAS regulation XI-1/7 requires that “suitable means shall be provided for the calibration of all such instruments”.1
- MSC.1/Circ.1561 interprets this as calibration on board or ashore in accordance with the manufacturer’s instructions, and says it does not refer to pre-operational accuracy tests.2
- MSC.1/Circ.1581 gives the same interpretation for the tanker oxygen and flammable vapour instruments of SOLAS II-2/4.5.7.1.6
- MSC.1/Circ.1477 paragraph 16 says the maker’s instructions should clearly define calibration requirements, and paragraph 17 says an over-due alarm should not stop the instrument working in use.8
- SOLAS regulation III/19.3.6.2.3 requires each enclosed space entry and rescue drill to include checking and use of instruments for measuring the atmosphere.3
- MSC.581(110) section 3.6 recommends recorded training in the maintenance, calibration and use of atmosphere testing equipment, with a list of crew deemed competent.4
- MSC.581(110) sections 6.5.3 and 8.2 recommend certified and calibrated instruments for the pre-entry test and calibrated and tested personal detectors for those who enter.4
- IGC Code paragraph 13.6.18 requires testing and calibration of gas detection equipment at regular intervals, with suitable equipment carried on board and used as the maker recommends.10
Flag and class notes
- Bahamas: “suitable means” may be calibration on board with the maker’s instructions and equipment, or ashore; if ashore, an alternative instrument must be on board; a valid calibration certificate should accompany the in-use instrument at all times; and if the maker recommends span gas of the correct mix, it must be carried for bump testing before use.5
- Marshall Islands: after a rise in US Coast Guard deficiencies, the Administrator reminded owners that instruments must be calibrated to the maker’s instructions, and that where calibration is done on board the crew must be trained, the maker’s calibration means must be on board and the SMS must cover calibration, testing and use.9 Its Marine Notice 7-041-1 also lists calibration of instruments to the maker’s instructions, on board or ashore, as part of the enclosed space drill.12
- Other flags publish similar notices; search your flag’s marine notices for “SOLAS XI-1/7” or “atmosphere testing instrument”.
Key numbers
| What | Value |
|---|---|
| Calibration means required since | 1 July 20161 |
| IMO interpretation (calibration on board or ashore) | MSC.1/Circ.1561, 28 November 20162 |
| Same interpretation for tanker instruments | MSC.1/Circ.1581, 16 June 20176 |
| Calibration interval | Maker’s instructions2 |
| Bump test or calibration check (industry practice) | before each day’s use7 |
| Calibration check tolerance (industry practice) | about ±10 to 20% of test gas7 |
| Full calibrations allowed after failed checks before removal (one maker’s guidance) | 27 |
| Drills that include checking and use of instruments | at least every 2 months3 |
What inspectors find
- The Marshall Islands Administrator reported a rise in US Coast Guard deficiencies for portable atmosphere testing instruments that were not properly calibrated.9
- Points inspectors and auditors check against these requirements: no calibration certificate on board, certificate for a different serial number, interval past the maker’s limit, span gas expired or of the wrong mix, no record of who is trained to calibrate.54
- Ships that rely on bump tests alone and treat them as calibration, which MSC.1/Circ.1561 rules out.2
- Instruments used with a failed sensor, so the meter no longer measures all four XI-1/7 gases.1
FAQ
Is a bump test a legal requirement?
SOLAS does not mention bump tests. They come from the maker’s instructions, which MSC.581(110) says should be strictly followed, and from flag requirements such as the Bahamas’ rule on carrying span gas. Most makers ask for one before each day’s use.
Can the crew calibrate the meter themselves?
Yes, if the maker allows it and the crew follow its procedure with its equipment and calibration gas. MSC.1/Circ.1561 accepts calibration on board. The crew must be trained and recorded, and the SMS should describe the procedure.
How long is span gas good for?
It depends on the mixture and cylinder; reactive gases such as H₂S have shorter lives. Use the expiry date printed on the cylinder and the maker’s advice, and order a replacement well before it runs out.
Who sets the alarm levels?
MSC.1/Circ.1477 paragraph 9 says alarms should activate at the levels set by the flag Administration. Where the flag sets none, the maker’s defaults and company procedures apply. Record them on the calibration certificate.
Quiz6 questions
Sources
- 1
IMO Resolution MSC.380(94), Amendments to SOLAS (adopted 21 November 2014, in force 1 July 2016), Annex, regulation XI-1/7. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.380(94).pdf
- 2
IMO MSC.1/Circ.1561, Unified interpretation of SOLAS regulation XI-1/7 (28 November 2016), Annex. Copy published by the Finnish Transport and Communications Agency (Traficom): https://www.traficom.fi/files/media/regulation/24358-MSC_1-Circ_1561_-_SOLAS_X-I-17_Calibration_of_portable_atmosphere_testing_instruments_.pdf
- 3
IMO Resolution MSC.350(92), Amendments to SOLAS (adopted 21 June 2013, in force 1 January 2015), Annex, regulation III/19 paragraphs 3.3 and 3.6. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.350(92).pdf
- 4
IMO Resolution MSC.581(110), Revised recommendations for entering enclosed spaces aboard ships (adopted 27 June 2025), Annex, sections 3.6, 6.5.3, 7.2 and 8.2. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.581(110).pdf
- 5
Indian Register of Shipping, Technical Circular 011/2017, The Bahamas National Requirements, Revision 08 (17 January 2017): atmosphere testing instruments, calibration. https://www.irclass.org/media/2668/technical-circular-no-11.pdf
- 6
IMO MSC.1/Circ.1581, Unified interpretations of SOLAS chapter II-2 (16 June 2017), Annex, regulation 4.5.7.1. Copy published by Traficom: https://www.traficom.fi/files/media/regulation/28723-MSC_1-Circ_1581_-_UI_Gas_measurement%2C_Tankers_SOLAS_Ch_II-2_.pdf
- 7
MSA Safety, What’s the difference between a bump test and calibration (summary of the ISEA Statement on validation of operation for direct reading portable gas monitors, March 2010). Industry practice, not an IMO requirement. https://blog.msasafety.com/whats-the-difference-between-a-bump-test-and-calibration-and-why-should-you-care/
- 8
IMO MSC.1/Circ.1477, Guidelines to facilitate the selection of portable atmosphere testing instruments for enclosed spaces (9 June 2014), Annex paragraphs 9, 16 and 17. Copy published by the Vietnam Maritime Administration: https://vimawa.gov.vn/f/circ%201477.PDF
- 9
Republic of the Marshall Islands Maritime Administrator advisory on improperly calibrated portable atmosphere testing instruments, as reported by SAFETY4SEA. https://safety4sea.com/rmi-beware-of-improperly-calibrated-portable-atmosphere-testing-instruments/
- 10
IMO Resolution MSC.370(93), Amendments to the IGC Code (adopted 22 May 2014; applies to gas carriers constructed on or after 1 July 2016), Annex, paragraph 13.6.18. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.370(93).pdf
- 11
IMO Resolution MSC.292(87), Amendments to the FSS Code (adopted 21 May 2010), Annex, new chapter 16, paragraph 2.2.3.4. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.292(87).pdf
- 12
Republic of the Marshall Islands Maritime Administrator, Marine Notice 7-041-1, Entering enclosed spaces: safety precautions (Rev. Jan/2026), paragraph 1.4.6. https://www.register-iri.com/wp-content/uploads/MN-7-041-1.pdf
Rules checked 20 October 2026. VSL Safety is not an approved training provider and doesn't issue certificates. These lessons don't replace STCW training, or the manufacturer's training and certification that service technicians need.
