Why do fleet engineers need a certified five gas detector?

Fleet engineers need a certified five gas detector because IMO Resolution MSC.581(110), which entered into force on 3 December 2025, now requires portable gas detectors used for enclosed space entry to measure at least five gases, including carbon dioxide (CO₂) as a mandatory parameter for the first time. This makes traditional four-gas detectors non-compliant for pre-entry atmospheric testing on board ships. Below, we answer the most practical questions fleet engineers and technical superintendents have about five gas detectors, from what they measure to how often they need servicing.

What gases does a five gas detector actually measure?

A compliant five gas detector measures oxygen (O₂), flammable gases expressed as a percentage of the Lower Explosive Limit (LEL), carbon monoxide (CO), carbon dioxide (CO₂), and at least one additional toxic gas, most commonly hydrogen sulphide (H₂S). This combination is now the minimum required configuration under the revised IMO recommendations for enclosed space entry.

Each of these gases plays a specific role in keeping crew safe before they step into a confined space:

O₂ confirms there is enough oxygen to breathe. Entry is only permitted when O₂ reads at or above 20.9% by volume.
LEL measures the concentration of flammable gases or vapours. The atmosphere must read below 1% of the Lower Flammability Limit before entry.
CO detects carbon monoxide, a colourless, odourless gas that can be present in cargo holds or engine-related spaces.
CO₂ is the newly mandated parameter. Entry is only permitted when CO₂ reads below 0.5% by volume (5,000 ppm). Standard percentage-range sensors lack the resolution to measure this accurately, which is why Non-Dispersive Infrared (NDIR) technology has become the benchmark for compliant CO₂ detection.
H₂S is the most common fifth gas, identified through risk assessment. It is frequently present in cargo tanks, sewage spaces, and areas where organic matter has decomposed.

One important point worth noting: CO₂ can build up in a space that contains no inherently dangerous cargo at all. Ordinary rusting in a damp, enclosed steel compartment consumes oxygen and elevates CO₂ levels. A cargo hold with bare steel and moisture can become dangerous within days, which is exactly why CO₂ measurement is now a hard requirement rather than an optional extra.

What certifications should a marine five gas detector have?

A marine five gas detector should carry ATEX or IECEx certification for use in potentially explosive atmospheres, along with approval from one or more recognised classification societies such as DNV, Lloyd’s Register, Bureau Veritas, or ABS. Type approval from a classification society confirms the device meets the technical standards required for use on board certificated vessels.

Beyond the explosion-protection rating, look for the following when selecting a compliant unit:

Classification society type approval relevant to the flag state and class of your vessels
NDIR sensor technology for CO₂ measurement, which provides the ppm-level resolution the regulation requires
Compliance with IMO Resolution MSC.581(110), either stated explicitly by the manufacturer or confirmed through the technical specification sheet
Calibration traceability to recognised national or international standards

Always verify that the specific model is approved for the gas types it claims to detect. A device marketed as a five gas detector is only compliant if all five sensors are individually certified and the unit has been tested as a combined instrument, not just as individual sensor components.

Why is certification required for confined space entry on ships?

Certification is required because uncertified instruments cannot be relied upon to produce accurate readings in the conditions found on board ships, and an inaccurate reading in a confined space can be fatal. IMO Resolution MSC.581(110) and the underlying SOLAS requirements both demand that atmospheric testing equipment be fit for purpose in a maritime environment, which means it must be certified for explosive atmospheres and validated for the specific gases being measured.

Port State Control inspectors treat an unrecorded or unverified test as a test that did not happen. If your gas detector is not certified, any readings it produces carry no regulatory weight. This creates direct liability for the master and the ship management company, and it exposes the vessel to detention.

There is also a practical reason. Ships operate in salt air, temperature extremes, and high humidity. Consumer-grade or uncertified instruments drift faster, are more prone to sensor degradation, and are not built to withstand the mechanical demands of daily shipboard use. Certification is the minimum assurance that the instrument will perform as labelled under those conditions.

For Port State Control purposes, maintaining a ship-specific Enclosed Space Register and pairing it with certified, calibrated instruments is now part of the inspection scope. RightShip RiSQ version 3.2 has already integrated these requirements, meaning the bar for compliance is being actively enforced across the industry.

How does a five gas detector differ from a single or two gas detector?

A five gas detector measures multiple atmospheric hazards simultaneously in a single instrument, while a single or two gas detector monitors only one or two specific gases. For enclosed space entry under current IMO requirements, single and two gas detectors are not sufficient on their own because they cannot confirm that all mandatory pre-entry parameters fall within safe limits at the same time.

Here is a practical comparison:

Single gas detector: Monitors one gas, such as H₂S or CO. Useful as a personal monitor in a known hazard environment, but not suitable as the primary pre-entry testing instrument for confined spaces.
Two gas detector: Typically monitors O₂ and one toxic gas. Still insufficient for confined space entry because it does not cover LEL, CO₂, or additional toxic gases.
Four gas detector (legacy standard): Usually monitors LEL, O₂, CO, and H₂S. This was the industry norm before MSC.581(110), but it does not include CO₂ and is no longer compliant for pre-entry testing under the revised recommendations.
Five gas detector (current standard): Covers all mandatory parameters including CO₂ with NDIR technology, making it the minimum compliant instrument for enclosed space entry on board ships as of December 2025.

If your vessel currently carries four-gas monitors, those units are not automatically obsolete for all purposes, but they cannot be used as the primary pre-entry instrument for confined spaces without an additional CO₂ measurement. Upgrading to a five gas detector is the straightforward solution. Our fire and gas detection range covers compliant options that can replace legacy four-gas units without disrupting your existing safety management procedures.

Which five gas detectors are compatible with existing onboard safety systems?

Most modern five gas detectors are standalone portable instruments that do not need to integrate with a fixed fire or gas detection panel to function. Compatibility in this context means the detector fits your existing calibration equipment, docking stations, data logging infrastructure, and crew training procedures, rather than electrical integration with a panel.

When assessing compatibility, focus on the following:

Calibration gas compatibility: Confirm that the five gas detector uses calibration gas mixtures you can already source, or that your existing calibration station supports the new unit.
Docking station and bump test compatibility: If you use an automated docking station for regular bump testing and calibration records, check whether the new five gas detector is supported by the same station or requires a new one.
Data logging and reporting: Some fleet management systems accept instrument data directly. Verify that the detector’s output format is compatible with your SMS documentation requirements.
Brand continuity: If your fleet already uses instruments from a specific manufacturer, staying within that brand family often simplifies crew training and spare parts management.

Older vessels that have been running four-gas monitors for years sometimes face a practical challenge: the calibration infrastructure and spare sensor stock are built around those units. In those cases, a phased replacement approach, starting with the vessels that face the most frequent enclosed space entry work, can help manage the transition without disrupting fleet-wide procedures.

How often does a five gas detector need calibration and servicing?

A five gas detector typically requires a bump test before each use, a full calibration at least every six months, and a comprehensive service annually, though the exact intervals depend on the manufacturer’s recommendations, classification society requirements, and the frequency of use on board. Always follow the intervals specified in the instrument’s documentation and your SMS.

Bump testing

A bump test exposes the detector to a known concentration of test gas to confirm that all sensors respond and the alarms activate. This is not a full calibration, but it is a quick and important check that the instrument is functioning before crew rely on it in a confined space. Most manufacturers and classification societies recommend bump testing before every use or at minimum once per day when the instrument is in active service.

Full calibration

A full calibration adjusts the sensor readings against a certified reference gas mixture and resets the instrument’s baseline. This should be carried out by a qualified technician using traceable calibration gases. The NDIR CO₂ sensor in a five gas detector is generally more stable than electrochemical sensors, but it still requires periodic calibration to maintain accuracy at the 5,000 ppm threshold the regulation specifies.

Keep records of every bump test and calibration. Under MSC.581(110), Port State Control inspectors treat undocumented testing as testing that did not occur. A well-maintained calibration log is part of demonstrating compliance, not just a paperwork exercise. Our service and repair team can support scheduled calibration and maintenance to keep your instruments compliant and your records complete.

How Lavastica helps with five gas detector compliance

Lavastica supplies, services, and advises on portable gas detection equipment for the maritime sector. Whether you need to replace legacy four-gas monitors across a fleet or source a single certified five gas detector quickly for a vessel in port, we can help you move fast without cutting corners on compliance. Here is what we offer:

Supply of certified five gas detectors from a broad range of manufacturers, including units with NDIR CO₂ sensors that meet the MSC.581(110) requirements
Compatibility advice to match new instruments with your existing calibration equipment, docking stations, and SMS documentation
Calibration and servicing carried out in our in-house workshop in Rotterdam, with fast turnaround to minimise vessel downtime
Obsolete equipment management for fleets transitioning away from four-gas monitors, including advice on phased replacement strategies
Emergency delivery through our worldwide logistics network when a vessel needs a compliant instrument urgently

Get in touch with us directly to discuss your fleet’s requirements. Learn more about who we are or contact our team for fast, practical advice. You can reach us by phone at +31 (0) 10 265 5070 or by email at [email protected].