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Gas detector false readings can create serious problems in the workplace. An instrument that reports inaccurate gas concentrations may trigger unnecessary alarms, fail to identify a real hazard, or give workers a false sense of security. Understanding why gas detectors produce inaccurate readings is the first step toward keeping equipment reliable and workers protected.
Several factors can affect gas detector accuracy, including sensor interference, calibration drift, environmental conditions, and sensor deterioration. Some problems can be addressed through routine maintenance and professional calibration. Others require sensor replacement, repairs, or a different detection solution.
Let’s look at some common causes of inaccurate gas readings and what you can do about them.
1. Gas Detector Cross-Sensitivity: When Other Gases Interfere
One common reason for unexpected gas detector readings is cross-sensitivity.
Cross-sensitivity occurs when a sensor responds to a gas other than the specific gas it was designed to detect. Depending on the sensor technology and the interfering gas, this response can produce a reading even when the target gas is not present.
For example, an electrochemical sensor designed to detect one toxic gas may also respond to certain other chemicals. The result could be an unexpected reading or an alarm that appears to have no obvious explanation.
Cross-sensitivity can also create a more concerning problem: an interfering gas may suppress a sensor’s response, potentially causing it to report a lower concentration than what is actually present.
What causes gas sensor interference?
- Exposure to other gases or chemical vapors.
- Cleaning products and industrial solvents.
- Chemicals commonly present in manufacturing environments.
- Interactions between different sensor technologies.
The specific gases that cause interference depend on the sensor manufacturer, sensor type, and instrument configuration. Manufacturers often provide cross-sensitivity charts that identify known interactions.
If your detector consistently produces unexpected readings in a particular environment, consult the manufacturer’s documentation and have the instrument evaluated by a qualified technician.
2. Calibration Drift: Why Gas Detector Readings Become Inaccurate Over Time
Another common cause of gas detector false readings is calibration drift.
Calibration drift occurs when a sensor’s reference point gradually changes. As a result, the detector may continue responding to gas exposure but display an inaccurate concentration.
Several factors can contribute to calibration drift:
- Normal sensor aging and chemical degradation.
- Exposure to high concentrations of target gases.
- Extreme temperatures or humidity.
- Dust, dirt, and other airborne contaminants.
- Physical shock, vibration, or rough handling.
- Exposure to chemicals that damage or degrade sensors.
Even a detector that looks perfectly fine on the outside may have internal components that affect its accuracy.
How does calibration help?
Gas detector calibration compares an instrument’s response against a known concentration of certified test gas. If the instrument’s reading is outside the manufacturer’s acceptable tolerance, a full calibration can adjust the instrument to match the known reference concentration.
Routine calibration helps identify measurement drift before inaccurate readings become a serious safety concern.
Routine gas detector calibration services help identify measurement drift before inaccurate readings become a serious safety concern.
However, calibration cannot repair a physically damaged sensor or eliminate every form of chemical interference. If a detector cannot be calibrated successfully, it may need professional repair or sensor replacement.
3. Sensor Poisoning and Deterioration
Gas detector sensors don’t last forever. Depending on the technology, operating environment, and chemical exposure, sensors can lose sensitivity or stop functioning properly.
Sensor poisoning occurs when exposure to certain substances interferes with a sensor’s ability to detect gas accurately. Some substances can permanently damage the sensing element.
For example, catalytic bead sensors used to detect combustible gases can be affected by certain silicones, sulfur compounds, and other chemicals. Electrochemical sensors can also deteriorate after exposure to solvents and corrosive substances.
Signs of a deteriorating or damaged sensor may include:
- Unexpected or inconsistent readings.
- Failure to respond during a bump test.
- Repeated calibration failures.
- Slow sensor response.
- Persistent error messages.
A calibration attempt may reveal that a sensor is no longer responding within acceptable limits. In these situations, replacing the sensor may be necessary.
Continuing to use a detector with a damaged or unreliable sensor can put workers at risk. Follow the manufacturer’s instructions and remove equipment from service when it fails required performance checks.
4. Environmental Conditions Can Affect Gas Detector Accuracy
Gas detectors are designed to operate within specified environmental conditions. Using them outside those conditions can affect sensor performance and produce unreliable measurements.
Temperature, humidity, atmospheric pressure, and airborne contaminants can all influence how certain sensors respond.
For example:
- Temperature changes: Extreme heat or cold can affect sensor response and instrument electronics.
- Humidity: High or low humidity can influence certain electrochemical sensors.
- Dust and particulates: Contaminants can obstruct sensor openings and interfere with gas reaching the sensing element.
- Chemical exposure: Solvents, corrosive gases, and other chemicals may affect sensor performance.
If your gas detector produces inconsistent readings when moving between different work environments, environmental conditions may be contributing to the problem.
Always check the manufacturer’s operating specifications and make sure the detector is suitable for the environment where it will be used.
5. Bump Testing vs. Gas Detector Calibration: What’s the Difference?
Bump testing and calibration are both important parts of gas detector maintenance, but they serve different purposes.
Understanding the difference is important because a detector can pass a bump test and still produce inaccurate gas concentration readings.
What is a bump test?
A bump test exposes the detector’s sensors to a known concentration of test gas to confirm that the sensors respond and the instrument’s alarms activate.
A bump test verifies basic functionality. It does not establish that the detector is accurately measuring gas concentrations.
What is a calibration check?
A calibration check compares the detector’s displayed reading against a known concentration of test gas. If the reading falls within the manufacturer’s acceptable tolerance, the instrument passes the check.
What is a full calibration?
A full calibration adjusts the instrument’s readings to match a known concentration of certified calibration gas.
If a detector fails a calibration check, a full calibration may be necessary. If it cannot be calibrated successfully, the instrument should be removed from service and evaluated by qualified personnel.
According to OSHA’s guidance on calibrating and testing direct-reading monitors, portable gas monitors should undergo an operational check before each day’s use, following manufacturer instructions. OSHA also explains the importance of using certified, traceable test gas and maintaining calibration records.
Always follow the manufacturer’s specific requirements for bump testing, calibration checks, and full calibration intervals.
6. When Should You Have Your Gas Detector Professionally Calibrated?
Routine gas detector calibration is essential for maintaining accurate measurements and dependable equipment.
However, calibration shouldn’t be something you think about only when a detector starts producing questionable readings.
Consider having your equipment evaluated when:
- Your detector fails a bump test or calibration check.
- Readings appear inconsistent or unexpected.
- The instrument has been exposed to extreme environmental conditions.
- The detector has experienced physical damage or significant impact.
- A sensor has been exposed to potentially damaging chemicals.
- Your manufacturer’s recommended calibration interval has arrived.
Keeping accurate service and calibration records also helps identify recurring problems and determine when sensors may need replacement.
Remember that calibration intervals vary depending on the instrument, sensor technology, manufacturer recommendations, and workplace conditions. There isn’t one schedule that applies to every gas detector.
Keep Your Gas Detectors Accurate with Professional Calibration from Apollo Safety
Whether you’re maintaining a single portable gas monitor or managing an entire facility’s detection equipment, Apollo Safety can help you keep your instruments in working order.
Not sure whether your gas detector needs calibration, repair, or a replacement sensor?
Contact Apollo Safety’s technical team at 508-673-2544 or learn more about our gas detector calibration and repair services.
Don’t wait for an inaccurate reading to become a workplace safety problem. Make sure your gas detection equipment is ready when you need it.
