Gas Detector Calibration vs Bump Testing: What’s the Difference?

Gas detection systems are only as reliable as the sensors inside them. Over time, those sensors can drift, degrade or become damaged and when that happens, workers may not receive a reliable warning of hazardous gas concentrations. That’s why calibration and bump testing are essential parts of maintaining safe, compliant gas detection equipment.

Below is a clear breakdown of what calibration really means, how bump testing fits in, and why neither can replace the other.

What Calibration Means

Calibration is the process of adjusting a detector’s response using a certified calibration gas and, where required, an appropriate zero gas such as clean air, synthetic air or nitrogen. This ensures the detector’s readings remain aligned with the actual concentration of gas present.

Three key concepts underpin calibration:

• Sensor drift – Over time, a sensor’s baseline shifts and its sensitivity can decrease. This can happen due to environmental conditions, ageing, or chemical changes inside the sensor.
• Detection capability – This refers to the detector’s ability to reliably detect the target gas within its specified operating range.
• Accuracy – How close the detector’s reading is to the true gas concentration.

If drift is left unchecked, sensors can degrade to the point where they no longer detect gases reliably, even if the device appears to be functioning normally.

Bump Testing: What Is It?

A bump test is a quick functional check. It exposes the detector to a known concentration of gas to confirm:

• The sensor responds.
• The alarms activate.
• The device is functioning as expected.

However, bump tests do not verify accuracy. They simply confirm that the detector reacts to the gas.

Recommended Bump Test Frequency

For portable gas detectors, bump testing is commonly carried out before each day’s use or in line with the manufacturer’s recommendations and the site’s risk assessment.

For fixed gas detection systems, functional testing should be carried out at intervals determined by the manufacturer, site procedures and the operating environment.

Full Calibration: What Is It?

Full calibration adjusts the detector’s response using a certified reference gas to ensure readings remain accurate and alarms activate at the correct set points.

Calibration should be carried out in accordance with the manufacturer’s recommendations and should also be considered if:

• Detector readings become inconsistent.
• The detector has suffered physical damage, such as being dropped.
• Repairs have been completed.
• Sensor performance is in doubt.
• The sensor shows signs of ageing or contamination.

Industry Standards

Many manufacturers recommend full calibration at six-month intervals. However, the appropriate frequency should always follow the manufacturer’s guidance, site conditions and previous maintenance results.

Equipment Needed

• Certified calibration gas cylinder.
• Compatible flow regulator
• .Detector-specific calibration cap.
• For automated testing, a manufacturer-approved docking station.

Calibration usually takes only a few minutes per detector, depending on the equipment being used.

Bump Tests vs Calibration: Why You Need Both

Bump tests confirm functionality.

Calibration confirms accuracy.

According to the International Safety Equipment Association (ISEA), bump testing helps identify silent failures, such as a sensor that displays 0 ppm because it’s blocked by dirt or contamination. The detector may appear to be working, but it may not respond correctly to hazardous gas.

A detector can pass a bump test and still produce inaccurate readings. Only calibration confirms that the detector is measuring gas concentrations correctly and that alarms will activate at the correct levels.

In the UK:

• Pre-use or daily bump testing is widely recommended for portable gas detectors.
• Calibration intervals should follow the manufacturer’s recommendations and the site’s maintenance procedures.

Sensor Drift, Poisoning and Lifespan

Environmental factors such as temperature, humidity and pressure can affect sensor performance. However, the main causes of degradation come from the internal chemical or physical processes used by different sensor technologies.

Catalytic Bead Sensors

Catalytic bead sensors can suffer from poisoning, where substances such as silicones, sulphur compounds or lead attach to the active surface and permanently reduce the sensor’s ability to detect combustible gases.

Electrochemical Sensors

Electrochemical sensors rely on internal electrolytes and naturally degrade over time through:

• Electrolyte depletion.
• Desiccation (loss of moisture).
• Flooding or moisture ingress into the sensor chamber.

Infrared (IR) Sensors

Infrared sensors detect gas using light rather than chemical reactions. Although they are generally more resistant to poisoning, they can still degrade over time due to ageing electronic components, contamination or obstruction of the optical path.

Overall

Bump tests ensure your detectors respond.

Calibration ensures your detectors respond accurately.

Both are essential for maintaining reliable gas detection and protecting workers from toxic or explosive gases. Relying on bump testing alone isn’t enough because only calibration confirms that a detector is measuring gas concentrations accurately.

At Protex, we support reliable maintenance across a wide range of fire and gas detection systems, including calibration, bump testing and ongoing preventative maintenance.

Our experienced engineers help ensure your equipment continues to perform as intended, giving you confidence that your gas detection system is ready when it matters most.