Gas Detection on Board Vessels - What Ship Operators Need to Know

The main gas hazards on board

Different spaces on board present different gas hazards. Understanding which gas types are relevant to each space is the starting point for any gas detection specification.

Ammonia (NH₃)
Ammonia is widely used as a refrigerant in vessel refrigeration systems, particularly on fishing vessels, reefer ships, and vessels with large cold storage capacity. It is toxic at low concentrations and has a distinctive odour, but in enclosed machinery spaces it can accumulate to dangerous levels before the smell alone provides adequate warning. Electrochemical sensors are used for ammonia detection.

Hydrogen (H₂)
Hydrogen is produced during the charging of lead-acid batteries and is increasingly relevant as LNG and hydrogen fuel cell propulsion systems become more common on commercial and passenger vessels. Battery rooms, hydrogen fuel storage areas, and fuel cell compartments all present hydrogen accumulation risk. Catalytic and infrared sensors are used for hydrogen detection depending on the application.

Carbon monoxide (CO)
Carbon monoxide from combustion engine exhaust is a risk in engine rooms, accommodation spaces with poor ventilation, and areas adjacent to exhaust systems. It is odourless, colourless, and acutely toxic at relatively low concentrations. Electrochemical sensors are the standard technology for CO detection.

Refrigerant gases
Modern HVAC systems and refrigeration plant on board vessels use a range of refrigerant gases - including R32, R410A, R1234YF, and other A2L refrigerants replacing older high-GWP gases under F-Gas Regulation. These gases are not acutely toxic but present flammability risks (A2L class) and asphyxiation risk in enclosed spaces. Infrared sensors are the appropriate technology for refrigerant detection.

Hydrocarbon gases (CH₄, LPG, propane, butane)
Relevant on LNG carriers, gas tankers, vessels with LPG fuel systems, and any vessel carrying hydrocarbon cargo. Catalytic and infrared sensors cover flammable hydrocarbon detection depending on the concentration range and application.

Oxygen depletion and enrichment (O₂)
Oxygen monitoring is required in enclosed spaces where inert gas systems are used - cargo tanks on tankers, for example - and in any space where oxygen depletion is a risk during maintenance or confined space entry. Electrochemical sensors are used for oxygen monitoring.

Where detection is required on board

The spaces requiring gas detection on a vessel depend on the vessel type, propulsion system, cargo, and applicable class society rules. The following are the most common locations across commercial vessel types:

Engine rooms - CO from combustion, hydrogen from battery charging, flammable gases from fuel systems. Zone 1 ATEX certified detectors are typically required.

Pump rooms - hydrocarbon vapours on tankers and product carriers. Zone 1 classification is standard for pump rooms.

Refrigeration machinery spaces - ammonia on vessels with NH₃ refrigeration, refrigerant gases on vessels with HFC or A2L systems.

Battery rooms and fuel cell compartments - hydrogen detection is mandatory where lithium-ion or lead-acid batteries are installed at significant scale. As hybrid and fully electric vessel numbers grow, this is an increasingly common detection requirement.

Cargo holds and tanks - hydrocarbon vapours on tankers, CO₂ in reefer containers, inert gas monitoring on LNG and chemical carriers.

Accommodation spaces and galleys - CO detection for crew safety, LPG monitoring where gas cooking is installed.

Open deck and enclosed deck areas - area-specific requirements depending on cargo and fuel type.

Certifications that matter for marine gas detection

Selecting a detector with the right technical specifications is only part of the specification process. For formally certified installations, the certification portfolio of the equipment matters as much as the detection performance.

ATEX - required for detectors installed in classified hazardous areas on board. The zone classification of each space determines whether Category 2 (Zone 1) or Category 3 (Zone 2) equipment is required. All Sensitron SMART 3G and SMART S series detectors carry ATEX certification.

MED (Marine Equipment Directive, 2014/90/EU) - required for safety equipment installed on EU-flagged vessels. MED certification means the equipment has been assessed against the harmonised standards applicable to marine safety equipment and is approved for use under the EU maritime regulatory framework. The Sensitron SMART S-MS detector and Multiscan ++MED control panel both carry MED certification.

Lloyd's Register and CCS - type approval from classification societies recognised globally. The SMART S-MS carries both Lloyd's Register Marine and CCS approval, covering a significant portion of the global fleet.

SIL (Safety Integrity Level) - increasingly specified for gas detection on vessels carrying hazardous cargo, LNG carriers, and offshore support vessels. SIL2 hardware / SIL3 software certification is standard across the Sensitron SMART 3G and SMART S series detectors.

IECEx - the international equivalent of ATEX, recognised outside the EU. For vessels trading internationally under non-EU flag states, IECEx certification alongside ATEX provides broader regulatory coverage.

Fixed vs portable detection - using both correctly

Fixed gas detection and portable gas detection serve different functions on board and are not interchangeable.

Fixed detectors monitor specific, permanently identified hazard points continuously - engine room bilges, refrigeration machinery spaces, battery rooms - and trigger automated alarms or ventilation systems when gas is detected. They are the primary layer of gas safety for the vessel in normal operation.

Portable detectors are carried by crew members during maintenance, confined space entry, tank inspections, and other work activities where a worker enters a space that may contain gas. They provide personal protection for the individual and are mandatory for confined space entry procedures under most flag state and class society requirements.

A correctly specified vessel gas detection system uses both. Fixed detectors cover the permanent hazard points; portable multi-gas detectors cover confined space entry and maintenance activities where workers move through spaces not covered by fixed systems.

Specifying a marine gas detection system

For ship operators, superintendents, and shipyards specifying gas detection for a newbuild or retrofit, the process typically follows four steps:

1. Hazardous area classification - confirm the zone classification of each space requiring detection, in line with class society rules and flag state requirements.

2. Gas hazard identification - identify the specific gases to be detected in each space and the appropriate sensor technology for each.

3. Equipment specification - select detectors with the correct ATEX category and certification portfolio for the installation and flag state. For EU-flagged vessels, confirm MED certification where required.

4. Control panel selection - select a control panel with sufficient input capacity for the number of detector points, RS485 capability if BMS integration is required, and SIL rating if functional safety requirements apply. For EU-flagged vessels, the Sensitron Multiscan ++MED provides a single MED-certified control solution.

Insatech Marine can support all four steps - from hazardous area classification advice and product selection through to certification documentation and worldwide supply from Denmark.