How do you test fixed gas detection systems on board between calibrations?

Between calibrations, you test a fixed gas detection system on board by performing regular bump tests, visual inspections, and functional checks of sensors, alarms, and control panels. These routine checks confirm the system is responding correctly without waiting for the next scheduled calibration. For maritime vessels, a structured testing routine is not just good practice — it is a requirement under flag state and classification society standards. Below, we cover the most common questions fleet engineers ask about keeping their fixed gas detection systems reliable between calibrations.

What is a bump test and how does it differ from calibration?

A bump test is a quick functional check that confirms a gas detector responds to a known concentration of test gas. You expose the sensor briefly to a gas sample and verify that it triggers an alarm above the set threshold. The test does not adjust or correct the sensor — it only confirms the detector is alive and responding. Calibration, by contrast, adjusts the sensor’s output to match a certified reference gas concentration, correcting any drift that has developed over time.

Think of it this way: a bump test tells you the detector reacts; calibration tells you it reads accurately. Both are important, and neither replaces the other. On board a vessel, bump tests are typically performed much more frequently than full calibrations because they are faster, require less equipment, and can be done by the ship’s own crew without specialist tools. Calibration usually requires certified reference gas and, depending on the system, a trained technician or a service and repair visit.

For fixed gas detection systems specifically, a bump test involves connecting a test gas cylinder to the sensor head via a calibration cap and confirming that the control panel registers the alarm condition. This is fundamentally different from portable detector bump testing because the sensor is wired into a larger system — the panel, relay outputs, and any connected suppression or ventilation systems must all respond correctly for the test to be considered valid.

How often should fixed gas detectors be tested between calibrations?

Fixed gas detectors on board should be bump tested at minimum once every three months, though many classification societies and flag states recommend monthly testing for sensors in high-risk locations such as engine rooms, pump rooms, and cargo holds. The exact interval depends on the sensor type, the environment, and the requirements of your vessel’s Safety Management System (SMS).

Sensors in harsh environments — high humidity, temperature extremes, exposure to oil mist or chemical vapors — degrade faster and should be tested more frequently. Electrochemical sensors used for toxic gases such as CO or H₂S are particularly sensitive to environmental stress and can lose sensitivity between calibrations without showing any outward sign of failure. Infrared sensors used for CO₂ detection, which are now required under IMO Resolution MSC.581(110) for enclosed space entry compliance, are more stable but still benefit from regular functional checks.

A practical approach for fleet engineers is to align bump test schedules with existing onboard maintenance routines — monthly safety rounds, quarterly equipment checks — so testing becomes part of a predictable workflow rather than an ad hoc task. Your SMS should document the required frequency for each sensor location, and that documentation will be reviewed during Port State Control inspections.

What checks can be done without test gas?

Several meaningful checks on a fixed gas detection system can be performed without any test gas at all. These visual and functional checks do not confirm sensor sensitivity, but they do identify faults in the system’s infrastructure that could prevent a valid alarm from reaching the bridge or control room.

Panel status check: Confirm the control panel shows no fault conditions and all zones are active and reporting normally.
Sensor head inspection: Check for physical damage, corrosion, blocked inlet ports, or contamination from paint, grease, or debris — all common on working vessels.
Cable and junction box inspection: Look for loose connections, water ingress, or damaged conduit, particularly in areas exposed to vibration or wash-down.
Alarm output test: Most panels include a built-in lamp test or alarm simulation function that activates audible and visual alarms without test gas — use this to confirm outputs are functioning.
Relay and output verification: Where fixed detectors are connected to ventilation shut-off, fire dampers, or suppression systems, verify that the relay outputs are correctly wired and responding to simulated alarm conditions from the panel.
Power supply check: Confirm the system is receiving the correct supply voltage and that backup power (where fitted) is operational.

These checks are valuable precisely because they catch infrastructure failures that a bump test alone would miss. A sensor might respond perfectly to test gas but fail to transmit the alarm if a cable connection has corroded. Running both types of checks together gives you a much more complete picture of system health.

Why might a fixed gas detector fail a between-calibration test?

A fixed gas detector can fail a bump test or functional check for several reasons, most of which are predictable and preventable. The most common cause is sensor poisoning or contamination — certain chemicals, particularly silicones, solvents, and paint fumes, can permanently damage electrochemical and catalytic bead sensors. On a working vessel, this is a realistic risk during maintenance periods.

Other common failure causes include:

Sensor end-of-life: All sensors have a finite service life, typically two to five years depending on type and environment. An aged sensor may still show a reading but respond too slowly or at too low a level to trigger an alarm at the correct threshold.
Blocked inlet: Dust, paint, or corrosion blocking the sensor’s sampling port prevents gas from reaching the sensing element — the detector appears operational but cannot detect anything.
Moisture ingress: Water inside a sensor head can short electrochemical cells or distort readings, particularly after wash-down or in high-humidity spaces.
Zero drift: Sensors can drift from their baseline reading over time, causing false readings or missed alarms even when the hardware appears intact.
Panel or wiring fault: The sensor itself may be functioning, but a fault in the panel or wiring prevents the alarm from registering correctly.

When a detector fails a test, the correct response is to take that zone out of service, post a physical warning, and arrange inspection or replacement before the space is used. Never assume a failed test result is a false alarm without investigation — on a vessel, the consequences of an undetected gas leak are severe.

How should test results be recorded for maritime compliance?

Test results for fixed gas detection systems should be recorded in a dedicated maintenance log that captures the date, location, sensor zone, test method used, result, and the name of the person who performed the test. For maritime compliance, this record must be available for inspection by Port State Control officers, class surveyors, and flag state auditors at any time.

A compliant record-keeping approach includes:

A system-specific logbook or digital maintenance record for the fixed gas detection installation, separate from general ship maintenance logs.
Documentation of both passed and failed tests — a log that only shows successful results will raise questions during an audit.
Records of any corrective actions taken following a failed test, including parts replaced, technicians involved, and the date the system was returned to service.
Calibration certificates kept on board and accessible, showing the reference gas used, concentration, and the technician or facility that performed the calibration.
Alignment with your Safety Management System — test records should be cross-referenced with the SMS maintenance schedule so auditors can confirm procedures are being followed consistently.

Under the updated enclosed space entry framework introduced by IMO Resolution MSC.581(110), atmospheric test results for pre-entry checks must also be recorded before any permit to work is issued. An unrecorded test is treated by inspectors as a test that did not occur. The same principle applies to your fixed system maintenance records — if it is not written down, it did not happen.

When should a fixed gas detector be replaced rather than recalibrated?

A fixed gas detector should be replaced rather than recalibrated when the sensor has reached the end of its rated service life, has been poisoned by chemical contamination, shows physical damage, or repeatedly fails bump tests despite recalibration attempts. Recalibration corrects drift — it cannot restore a fundamentally degraded sensor.

Specific situations that call for replacement rather than recalibration include:

The sensor is beyond its manufacturer-recommended service life (typically two to five years for electrochemical sensors).
The sensor fails to respond to test gas even after recalibration and cleaning.
The sensor has been exposed to known poisons such as silicone compounds, lead, or high concentrations of solvents.
Physical inspection reveals cracked housings, corroded contacts, or water damage inside the sensor head.
The detector is no longer capable of measuring all required gases — for example, a legacy sensor that cannot detect CO₂ in the ppm range required under current IMO recommendations.

Compatibility with your existing panel is an important consideration when replacing sensors. Not all replacement sensors are interchangeable, and using an incompatible unit can cause communication errors, incorrect alarm thresholds, or a complete loss of that detection zone. Always verify that a replacement sensor is approved for use with your specific control panel before installation.

How Lavastica helps with fixed gas detection testing and maintenance

We understand that keeping a fixed gas detection system compliant between calibrations takes more than good intentions — it takes the right parts, the right knowledge, and a supplier who responds when you need them. At Lavastica, we support fleet engineers and technical superintendents with:

Replacement sensors and spare parts for a wide range of fixed gas detection systems, including hard-to-find components for older installations.
Compatibility advice to ensure replacement sensors and components work with your existing control panels and system architecture.
Calibration and repair services from our in-house workshop in Rotterdam, with fast turnaround to minimize vessel downtime.
Technical support on testing procedures, compliance requirements, and which products meet current IMO and classification society standards.
Emergency service for urgent situations when a sensor failure cannot wait for a scheduled maintenance visit.

If you have questions about testing your fixed gas detection system or need parts quickly, our team is ready to help. Learn more about who we are or contact us directly for fast, practical support.

Phone: +31 (0) 10 265 5070Email: [email protected]