How do you choose the right gas detector for your vessel?

Choosing the right gas detector for your vessel starts with understanding which gases you need to monitor, what regulations apply to your ship type and trade, and whether the detector is compatible with your existing onboard systems. For most vessels, a compliant detector must now measure at least five gases, including oxygen, flammable gases, carbon monoxide, carbon dioxide, and at least one additional toxic gas. The sections below walk through every practical question you need to answer before making a purchase decision.

What types of gas detectors are used on ships?

Ships use two main categories of gas detectors: fixed gas detection systems and portable handheld detectors. Fixed systems are permanently installed in engine rooms, pump rooms, cargo holds, and other high-risk spaces, providing continuous monitoring and alarm output to a central panel. Portable detectors are carried by crew members and used for pre-entry atmospheric testing of enclosed spaces before anyone steps inside.

Within those two categories, you will find single-gas detectors designed to measure one specific gas, and multi-gas detectors that combine several sensors in one unit. The industry has long relied on four-gas monitors measuring oxygen (O₂), flammable gases (LEL), carbon monoxide (CO), and hydrogen sulphide (H₂S). However, following IMO Resolution MSC.581(110), which entered into force on 3 December 2025, a five-gas detector capable of also measuring carbon dioxide (CO₂) is now the required standard for enclosed space entry.

Fixed systems are typically integrated with the ship’s fire and gas detection panel, triggering alarms, ventilation, or shutdown sequences automatically. Portable detectors operate independently and are used on demand. Both types serve different purposes, and most vessels need both.

What gases should a vessel be detecting onboard?

At a minimum, vessels should be detecting 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 identified through risk assessment, most commonly hydrogen sulphide (H₂S). These five parameters are now the regulatory baseline for enclosed space entry under MSC.581(110).

The acceptable atmospheric limits for safe enclosed space entry are:

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

It is worth understanding why CO₂ has become a mandatory parameter. Ordinary rusting in a damp, confined space consumes oxygen and elevates CO₂ levels rapidly. A space does not need to carry hazardous cargo to become lethal. Bare steel and moisture alone can create an asphyxiation hazard within days. Beyond enclosed spaces, tankers, gas carriers, and vessels carrying specific bulk cargoes will have additional detection requirements tied to their cargo type and class notation.

How do SOLAS and classification society rules affect your choice?

SOLAS sets the baseline legal requirements for gas detection on ships, while classification societies such as Lloyd’s Register, DNV, Bureau Veritas, and others add their own technical standards on top. Your detector must satisfy both layers before it can be used on a compliant vessel. The specific rules that apply depend on your ship type, trade area, and flag state.

SOLAS Regulation XI-1/7 requires ships to carry portable gas detectors, and SOLAS Regulation III/19 mandates enclosed space entry and rescue drills. IMO Resolution MSC.581(110) now raises the bar by specifying that those portable detectors must be capable of measuring at least five gases, with CO₂ as a newly mandatory parameter. Classification societies may impose additional requirements for fixed detection systems in machinery spaces, cargo pump rooms, or battery rooms depending on the vessel type.

When selecting a detector, check that it carries the relevant type approvals for your flag state and classification society. Not all detectors certified for industrial use are accepted for maritime applications. A detector that works perfectly in an offshore facility may not meet the specific approval requirements of your classification society, so always verify certification before purchasing.

What’s the difference between catalytic bead, electrochemical, and infrared sensors?

The sensor technology inside a gas detector determines what it can measure, how accurately it measures, and how well it holds up over time. The three most common technologies in maritime gas detectors are catalytic bead sensors, electrochemical sensors, and infrared sensors, and each has a different application.

Catalytic bead sensors

Catalytic bead sensors, also called pellistors, detect flammable gases by measuring the heat generated when gas oxidises on a catalytic surface. They are robust, cost-effective, and widely used for LEL measurement. Their limitation is that they can be poisoned by silicones, lead compounds, or halogenated gases, which permanently damage the sensor and cause false readings. They also require oxygen to function, so they will not work reliably in oxygen-depleted atmospheres.

Electrochemical sensors

Electrochemical sensors measure toxic gases such as CO, H₂S, and O₂ by detecting the electrical current produced by a chemical reaction at the sensor electrode. They are accurate, relatively affordable, and the standard choice for CO and O₂ measurement. However, they have a limited service life, typically two to three years, and can drift over time if not regularly calibrated. For CO₂ measurement in the ppm range required by MSC.581(110), electrochemical sensors lack the resolution needed to accurately detect the 5,000 ppm regulatory limit.

Infrared sensors

Infrared (IR) sensors, particularly Non-Dispersive Infrared (NDIR) sensors, are now the benchmark for CO₂ measurement in compliant five-gas detectors. NDIR technology detects gas concentration by measuring how much infrared light a gas absorbs at a specific wavelength. It is highly stable, not affected by oxygen depletion, and provides the high-resolution ppm monitoring needed to accurately detect dangerous CO₂ build-up. IR sensors are also used for hydrocarbon detection in environments where catalytic bead sensors would be unreliable. Their higher cost is offset by longer service life and superior stability.

How do you check if a gas detector is compatible with your existing system?

Compatibility between a new gas detector and your existing onboard systems depends on three factors: signal output type, communication protocol, and physical installation interface. Before purchasing any detector, confirm that its output matches what your control panel or monitoring system expects to receive.

For fixed detectors connected to a central gas detection panel, the most common signal outputs are 4-20 mA analogue signals and digital protocols such as Modbus or proprietary manufacturer protocols. A detector with a 4-20 mA output will generally connect to most panels, but digital protocol detectors are often only compatible with panels from the same manufacturer or those specifically configured to accept that protocol.

For portable detectors, compatibility is less about panel integration and more about whether the device meets the same calibration gas standards used by your existing fleet of instruments. Using the same calibration gas across all portable detectors simplifies your maintenance programme and reduces the risk of calibration errors.

Rather than replacing an entire fleet of functional four-gas detectors, a practical approach is to supplement existing equipment with a dedicated standalone CO₂ detector. This bridges the regulatory gap introduced by MSC.581(110) without the capital expenditure of a full fleet replacement. Our fire and gas detection range includes options that work alongside existing equipment, and our technical team can advise on which combination meets your specific panel and flag state requirements.

When should you replace a gas detector instead of recalibrating it?

A gas detector should be replaced rather than recalibrated when it consistently fails bump tests, when sensor response time has slowed beyond the manufacturer’s specification, when the unit is physically damaged, or when the sensor has reached the end of its rated service life. Calibration corrects drift, but it cannot restore a sensor that is chemically exhausted or mechanically compromised.

Practical indicators that replacement is the right decision include:

The detector fails to reach the correct reading during a bump test even after calibration
Electrochemical sensors are beyond their rated lifespan, typically two to three years for CO and H₂S sensors
The unit has been exposed to sensor-poisoning substances such as silicones or lead compounds
The display, alarm, or battery no longer functions reliably
The detector does not meet the new five-gas requirement under MSC.581(110) and cannot be upgraded with a CO₂ sensor module
The manufacturer no longer supports the model with spare parts or calibration gas

Recalibration is a maintenance task, not a repair. It adjusts the detector’s output to match a known reference gas concentration, but it does not fix a failing sensor. A detector that requires unusually frequent calibration to stay within tolerance is telling you the sensor is deteriorating. At that point, the cost and risk of continued recalibration outweigh the cost of replacement. Our service and repair team can assess whether your current detectors are worth maintaining or whether replacement is the more reliable path forward.

How Lavastica helps you choose the right gas detector

Selecting the right gas detector involves more than picking a model from a catalogue. It requires matching sensor technology to the gases present on your vessel, verifying compliance with current IMO and classification society requirements, and confirming that the new equipment works with what you already have installed onboard. We help you work through each of those steps.

Regulatory guidance: We advise on which detectors meet the requirements of MSC.581(110) and your specific flag state and classification society
Compatibility assessment: We check whether new detectors integrate with your existing fixed detection panels or portable instrument fleet
Sensor technology advice: We help you select the right sensor type, including NDIR CO₂ sensors, for your specific application
Supplement or replace: Where possible, we identify whether supplementing existing equipment with a standalone CO₂ detector is a practical alternative to full fleet replacement
Fast delivery: We maintain stock of gas detection equipment in Rotterdam and can arrange worldwide delivery to minimise port time
Calibration and service support: Our in-house workshop handles calibration, repair, and overhaul to keep your detectors in working order

Whether you need a single replacement unit or advice on upgrading your entire detection setup, we are ready to help. Learn more about our expertise or contact us directly to discuss your situation. You can reach us by phone at +31 (0) 10 265 5070 or by email at info@lavastica.com.