What is a gas detector used for on ships?

On ships, a gas detector monitors the atmosphere for dangerous gases that can harm crew members or create fire and explosion hazards. These devices detect gases like oxygen deficiency, flammable vapors, carbon monoxide, hydrogen sulfide, and carbon dioxide in spaces ranging from engine rooms to cargo holds. Whether fixed or portable, gas detectors are a legal requirement under international maritime regulations and a practical lifeline for anyone working in confined or enclosed spaces onboard. This article covers the key questions every fleet engineer or technical superintendent should be able to answer about gas detection at sea.

What types of gases do gas detectors monitor on ships?

Gas detectors on ships typically monitor four core gases: oxygen (O2), flammable gases measured as a percentage of the Lower Explosive Limit (LEL), carbon monoxide (CO), and hydrogen sulfide (H2S). These are the standard parameters covered by most “4-in-1” portable detectors. However, updated regulations now also require monitoring for carbon dioxide (CO2) in many enclosed space scenarios.

Here is a quick overview of what each gas indicates and why it matters onboard:

Oxygen (O2): Normal atmospheric oxygen sits at around 20.9%. Levels below 19.5% are considered oxygen-deficient and immediately dangerous. Enclosed spaces like cargo holds and ballast tanks are prone to oxygen depletion through rusting, organic decomposition, or cargo absorption.
Flammable gases (LEL): Any reading above 10% LEL signals a serious fire or explosion risk. Fuel vapors, methane, and other hydrocarbons can accumulate in pump rooms, bilges, and fuel storage areas.
Carbon monoxide (CO): A colorless, odorless gas produced by incomplete combustion. It builds up in engine spaces, incinerator rooms, and anywhere fuel burns without sufficient ventilation.
Hydrogen sulfide (H2S): Extremely toxic even at low concentrations. Common in sewage tanks, cargo holds carrying organic materials, and crude oil tankers.
Carbon dioxide (CO2): Increasingly regulated as a mandatory test parameter. CO2 can accumulate in enclosed spaces due to the oxidation of iron (rusting) in damp conditions, even without any dangerous cargo present.

The inclusion of CO2 as a required parameter is a significant shift in how gas detection is approached at sea, and it has direct implications for which detector models are actually compliant today.

How does a gas detector work on a vessel?

A gas detector works by continuously sampling the surrounding atmosphere and triggering an alarm when a gas concentration exceeds a preset threshold. Most detectors use one or more sensor technologies, each suited to detecting specific types of gas. The detector processes the sensor signal, compares it against calibrated alarm levels, and alerts the crew visually and audibly when action is needed.

The two most relevant sensor technologies for maritime use are:

Electrochemical sensors: Used for toxic gases like CO, H2S, and O2. These sensors generate a small electrical current proportional to the gas concentration. They are reliable and accurate but have a limited lifespan and require regular calibration.
Catalytic bead (pellistor) sensors: Used for detecting flammable gases at LEL levels. They work by measuring the heat produced when a gas oxidizes on a heated bead. Effective for hydrocarbon vapors in engine rooms and pump rooms.
Non-Dispersive Infrared (NDIR) sensors: Now considered the benchmark for CO2 detection. NDIR sensors measure how much infrared light a gas absorbs at a specific wavelength. They provide the high-resolution ppm-level accuracy needed to reliably detect CO2 at the 5,000 ppm (0.5%) regulatory limit. Standard electrochemical sensors cannot measure CO2 at this resolution.

Understanding which sensor technology is inside your detector matters when assessing whether your current equipment is compliant with the latest requirements. Not all detectors that claim CO2 detection can actually measure at the accuracy level that regulations now demand.

Where are gas detectors installed on a ship?

Gas detectors are installed in any location onboard where dangerous gas accumulation is a realistic risk. Fixed detectors are permanently wired into the ship’s fire and gas detection system, while portable units are brought into spaces before and during entry. The specific locations depend on the vessel type, cargo carried, and applicable classification society rules.

Common installation locations for fixed gas detectors include:

Engine rooms and machinery spaces: To detect fuel vapors, refrigerant leaks, and CO from combustion equipment.
Pump rooms on tankers: High-risk areas where hydrocarbon vapors can accumulate rapidly.
Cargo holds: Particularly on vessels carrying cargo that depletes oxygen or emits toxic gases.
Battery rooms: Hydrogen gas can build up during charging of lead-acid batteries.
CO2 room and fire suppression system spaces: To detect accidental CO2 release before crew entry.
Accommodation areas: CO detectors near galley equipment or heating systems.

For portable detectors, the requirement is simpler: they must be used before and during entry into any enclosed or confined space, regardless of whether a fixed system is present. This includes ballast tanks, void spaces, cargo holds, and any space that has been sealed or poorly ventilated. Gas detection systems for maritime use are designed to integrate with existing alarm panels, which means compatibility with your current installation is always worth checking before selecting new equipment.

What regulations require gas detectors on ships?

Gas detectors on ships are required under several international maritime regulations. SOLAS Chapter XI-1, Regulation 7 mandates that ships carry portable atmosphere testing instruments, including devices capable of measuring oxygen, flammable gases, hydrogen sulfide, and carbon dioxide. SOLAS Chapter III, Regulation 19 requires enclosed space entry and rescue drills. Beyond SOLAS, classification societies such as DNV, Lloyd’s Register, and Bureau Veritas set additional technical requirements for fixed detection systems.

A significant regulatory development took effect with the endorsement of IMO Resolution MSC 581(110) on 3 December 2025. This resolution, titled the Revised Recommendations for Entering Enclosed Spaces on Board Ships, supersedes the older Resolution A.1050(27) and introduces a more rigorous framework for confined space safety. Key changes include:

Mandatory CO2 monitoring: CO2 is now a required pre-entry test parameter. Entry is only permitted when CO2 levels are confirmed below 0.5% (5,000 ppm). Most legacy 4-in-1 detectors cannot measure CO2 at this resolution.
NDIR technology as the benchmark: Non-Dispersive Infrared sensors are now the standard for CO2 detection because they provide the ppm-level accuracy that electrochemical sensors lack.
Expanded definitions of hazardous spaces: Connected spaces (linked by doors, trunks, or manholes) and adjacent spaces (sharing a common bulkhead) must now be treated as potentially hazardous until proven otherwise.
Mandatory Enclosed Space Register: Ships must maintain a vessel-specific register onboard and synchronize it with the shore-side office in real time.
Stricter procedural rules: Solo entry is prohibited, entry permits are valid for a maximum of 8 hours, and any break in work or ventilation immediately voids the permit.

RightShip RiSQ version 3.2 has already integrated MSC 581(110) requirements into its inspection scope, which means Port State Control inspectors are actively checking for compliance. If your vessels are still relying on older 4-gas monitors without CO2 capability, that is a compliance gap worth addressing now.

What is the difference between fixed and portable gas detectors on ships?

Fixed gas detectors are permanently installed at specific locations onboard and continuously monitor the atmosphere without crew intervention. Portable gas detectors are handheld devices carried by crew members and used on demand, particularly before entering enclosed or confined spaces. Both types serve different but complementary purposes, and most vessels require both.

Fixed detectors provide round-the-clock monitoring of high-risk areas. They are wired into the ship’s central fire and gas detection panel, trigger automated alarms, and can activate suppression systems. They are ideal for spaces that cannot be entered frequently for manual checks, such as pump rooms, battery compartments, and cargo holds on unmanned vessels.
Portable detectors give crew members real-time readings as they move through a space. They are used for pre-entry testing, continuous personal monitoring during confined space work, and spot checks in areas not covered by fixed systems. Under MSC 581(110), portable detectors must now be capable of measuring CO2 at ppm-level accuracy, which rules out many older models.

When selecting equipment, compatibility with your existing panel and alarm system is a practical consideration. A new fixed detector that does not communicate with your current detection panel creates integration problems and potential gaps in your alarm coverage. Our service and repair team regularly assists with exactly these kinds of compatibility assessments, helping you add or replace components without disrupting what is already working onboard.

How often should gas detectors on ships be tested and calibrated?

Gas detectors on ships should be functionally tested before each use and calibrated at intervals specified by the manufacturer, typically every six to twelve months. Classification societies and flag state requirements may set additional mandatory intervals. Bump testing (exposing the sensor to a known gas concentration to confirm it responds) should be performed before every confined space entry.

Here is a practical maintenance schedule to follow:

Before each use (bump test): Expose the detector to a certified test gas to confirm all sensors respond and alarms activate correctly. This takes less than a minute and is non-negotiable before any enclosed space entry.
Monthly: Inspect the device for physical damage, check battery condition, and verify sensor expiry dates.
Every 6 to 12 months (calibration): Full calibration using certified reference gases, performed by a qualified technician. This resets the sensor baseline and ensures readings are accurate across the full measurement range.
Sensor replacement: Electrochemical sensors have a limited lifespan, typically two to three years. Replace them proactively rather than waiting for failure.

Documentation is just as important as the testing itself. Under MSC 581(110), an unrecorded test is treated by Port State Control inspectors as a test that did not occur. Every bump test, calibration, and sensor replacement should be logged in the vessel’s safety management system and reflected in the Enclosed Space Register.

How Lavastica helps with gas detection on ships

Lavastica supplies and supports a wide range of gas detection equipment for maritime applications, from portable 4-gas and 5-gas monitors to fixed detection systems that integrate with your existing onboard installation. We understand that finding equipment that works with what you already have is often just as important as finding equipment that meets the latest regulations.

Supply of portable and fixed gas detectors from more than 100 brands, including models with NDIR CO2 sensors that comply with MSC 581(110)
Compatibility advice to ensure new detectors work with your existing fire and gas detection panels
Calibration and repair services from our in-house workshop in Rotterdam
Fast worldwide delivery to minimize time in port
Technical support on regulatory compliance and product selection
Replacement options for obsolete or end-of-life detector models

Whether you need a single replacement sensor or a complete system upgrade, we are ready to help. Learn more about us or contact us directly for fast, practical advice. You can reach us by phone at +31 (0) 10 265 5070 or by email at [email protected].