How do you ensure gas detector compliance during port inspections?

To ensure gas detector compliance during port inspections, your portable gas detectors must be capable of measuring at least five gases, including oxygen, flammable gases, carbon monoxide, carbon dioxide, and at least one additional toxic gas. Since IMO Resolution MSC.581(110) entered into force on 3 December 2025, the traditional four-gas detector is no longer sufficient. Below, we answer the most common compliance questions Fleet Engineers and Technical Superintendents face when preparing for port state control visits.

What do port state control inspectors actually check on gas detectors?

Port state control (PSC) inspectors check whether your portable gas detectors are capable of measuring the required gases, whether calibration records are current, and whether the equipment is properly maintained and ready for use. Since MSC.581(110) came into force, inspectors are also looking specifically for CO2 measurement capability, which was not previously mandatory.

In practice, a PSC inspection related to gas detection typically covers the following points:

Sensor configuration: Does the detector measure at least five gases, including CO2?
Calibration documentation: Are calibration certificates on board and up to date?
Enclosed Space Register: Is the vessel-specific register maintained both on board and ashore?
Permit to Work records: Are atmospheric test results recorded before each enclosed space entry?
Entrance control: Are hazardous entry points physically marked and locked when not in use?

One point that catches many vessels off guard: an unrecorded atmospheric test is treated by inspectors as a test that did not occur. If your crew tested the atmosphere before entering an enclosed space but failed to write it down, the inspection record will reflect a non-compliance. Documentation is just as important as the equipment itself.

Inspectors working within frameworks such as RightShip RiSQ version 3.2 have already incorporated MSC.581(110) requirements into their inspection scope, so this is not a future concern. It is a current one.

Which international regulations govern gas detectors on ships?

Gas detectors on ships are governed primarily by SOLAS and IMO resolutions. SOLAS Regulation XI-1/7 requires ships to carry portable gas detectors, while SOLAS Regulation III/19 mandates enclosed space entry and rescue drills. The technical requirements for what those detectors must measure are set out in IMO Resolution MSC.581(110), which entered into force on 3 December 2025.

MSC.581(110), titled the Revised Recommendations for Entering Enclosed Spaces on Board Ships, replaces the older Resolution A.1050(27). While SOLAS sets the baseline obligation to carry gas detection equipment, MSC.581(110) defines the technical standard that equipment must meet. The most significant change it introduces is the mandatory measurement of carbon dioxide (CO2), a parameter that was not required under the previous framework.

The acceptable atmospheric limits under MSC.581(110) are:

Oxygen (O2): at or above 20.9% by volume (certain flag states may permit a minimum of 19.5%)
Carbon dioxide (CO2): below 0.5% by volume (5,000 ppm)
Flammable gases: below 1% of the Lower Explosive Limit (LEL)
Toxic gases: below 50% of the applicable Occupational Exposure Limit (OEL)

Classification societies and flag state administrations may apply additional requirements on top of these IMO standards, so it is worth verifying the specific requirements that apply to each vessel in your fleet. That said, MSC.581(110) represents the current industry benchmark and is the primary reference point for port state control inspections worldwide.

How often do gas detectors need to be calibrated and tested?

Gas detectors used for enclosed space entry must be calibrated regularly, with most manufacturers and classification societies recommending bump testing before each use and full calibration at intervals defined by the manufacturer, typically every six to twelve months. Calibration records must be kept on board and available for inspection.

There is an important distinction between a bump test and a full calibration:

Bump test: A quick functional check using a known concentration of gas to confirm the sensors respond correctly. Recommended before every use in a safety-critical situation.
Full calibration: A precise adjustment of sensor readings against certified reference gas, performed at defined intervals and documented with a calibration certificate.

Under MSC.581(110), the requirement for CO2 measurement using Non-Dispersive Infrared (NDIR) technology adds a layer of complexity. Standard electrochemical sensors lack the resolution to accurately detect CO2 at the 5,000 ppm regulatory limit. NDIR sensors, which are now the benchmark for compliant CO2 detection, have their own calibration requirements and drift characteristics. Make sure your calibration regime accounts for the specific sensor technology in your detectors, not just a generic interval.

Our service and repair team can support calibration, bump testing, and maintenance for a wide range of detector brands and models, including units already installed on board.

What happens when a gas detector fails a port inspection?

If a gas detector fails a port state control inspection, the inspector can issue a deficiency report and, in serious cases, detain the vessel until the deficiency is resolved. A detained vessel cannot leave port, which directly translates into costly idle days. The financial and operational pressure this creates is significant.

Common reasons gas detectors fail inspections include:

Missing CO2 measurement capability (the most common issue since MSC.581(110) entered into force)
Expired or missing calibration certificates
Sensors that are outside their operational range or showing drift
Inadequate documentation of pre-entry atmospheric tests
Equipment that is present on board but not functional or ready for use

The fastest path to resolving a deficiency is having a replacement or supplementary detector available immediately. This is where preparation matters far more than reaction. If your existing four-gas detectors do not measure CO2, the recommended approach is to supplement them with a dedicated standalone CO2 detector rather than replacing the entire fleet. This bridges the regulatory gap without the cost and lead time of a full equipment replacement, and it is a practical solution that many vessels have already adopted.

Permit to Work procedures are also inspected closely. No permit may exceed a validity of 8 hours. If work is paused or ventilation stops, the permit becomes void immediately and all personnel must evacuate. Re-entry requires a fresh atmospheric test, and the results must be recorded before work resumes.

How do you replace an obsolete gas detector while staying compliant?

Replacing an obsolete gas detector while staying compliant means selecting a unit that meets the five-gas minimum requirement under MSC.581(110), is compatible with your existing onboard procedures and calibration infrastructure, and comes with the necessary certifications for maritime use. The key is matching the replacement to what is already installed, not just buying the newest model available.

Compatibility with existing equipment is a practical concern that is easy to overlook. Your crew is trained on specific equipment. Your calibration station may be set up for a particular sensor technology. Your spare parts stock is built around a specific brand. Switching to a completely different system creates new training requirements, new spare parts needs, and potential gaps in your Safety Management System documentation.

A structured approach to replacing obsolete gas detectors looks like this:

Audit your current equipment: Identify which detectors are missing CO2 capability and which are approaching end of life.
Assess the gap: Determine whether a supplementary standalone CO2 detector is sufficient or whether a full replacement is needed.
Check compatibility: Confirm that the replacement unit works with your existing calibration setup and that your crew can be trained quickly.
Verify certifications: Ensure the new unit carries the relevant maritime approvals and meets NDIR requirements for CO2 detection.
Update your SMS: Revise your Safety Management System to reflect the new equipment, updated procedures, and revised risk assessment forms aligned with MSC.581(110).
Train your crew: Conduct drills that include practical use of the new detector, not just a muster.

Enclosed space drills must now be held at least once every two months and must include hands-on use of atmospheric testing instruments. This means your crew needs to be genuinely familiar with the equipment, not just aware of its existence. Explore our range of fire and gas detection equipment for maritime-certified options that meet the current requirements.

How we help with gas detector compliance

At Lavastica, we work with Fleet Engineers and Technical Superintendents every day who are dealing with exactly these challenges. We understand that a vessel in port is costing money, and that finding the right compliant replacement quickly is not always straightforward. Here is how we can help:

Supply of compliant gas detectors: We stock five-gas detectors with NDIR CO2 capability from more than 100 brands, ready for fast worldwide delivery.
Standalone CO2 detectors: If your existing four-gas units are functional and calibrated, we can supply a dedicated CO2 detector to bridge the compliance gap without replacing your entire fleet.
Calibration and repair: Our in-house workshop handles calibration, maintenance, and repair for a wide range of gas detection equipment, including older and obsolete models.
Obsolete equipment management: We maintain stock of refurbished and end-of-life products, and we can advise on compatible replacements that integrate with your existing onboard systems.
Technical advice: Not sure which detector works with your current setup? We give you straightforward advice on compatibility and compliance, without pushing you toward unnecessary replacements.

Get in touch with our team directly. We respond fast because we know every hour in port counts. Learn more about who we are or contact us today.

Phone: +31 (0) 10 265 5070
Email: info@lavastica.com