As part of the Department of Labor, the Occupational Safety and Health Administration (OSHA) implements many workplace safety regulations. The agency does not have a standard or regulation related to gas detector calibration. Despite this, it has released guidelines through a Safety and Health Information Bulletin. This bulletin has important information that can help employers complete gas detector calibration safely. 

Portable gas monitors are designed to alert employees and contractors of toxic gases or oxygen deficiencies in workspaces. The improper calibration of these devices can lead to exposure to hazardous gases. It can also lead personnel into oxygen-deficient environments. Exposure can lead to illness, injury, or death. When hazardous gases accumulate, there is the threat of explosion. Explosions can be devastating in terms of loss of life and loss of property. 

Calibration Basics

OSHA recommends developing standard procedures for gas detector calibration. Recommendations include documentation to support the proper maintenance and timely calibration of these instruments. Gas detector calibration refers to an instrument’s measuring accuracy relative to a known traceable concentration of test gas. The detector compares the sensor’s response to a known concentration of test gas. To confirm the accuracy of the response, it’s crucial to use calibration gas that has not expired. 

Gas detector calibration should be completed in environmental conditions that are the same (or similar to) the actual workplace conditions. This process is recommended because detectors may have sensitivity to temperature and humidity variances. 

Regular gas detector calibration should also conform to the manufacturer’s instructions. In addition to this, company policy and any appropriate agency guidelines should be followed. This level of detail can ensure that proper gas detection calibration procedures are followed. These procedures ensure the gas detectors operate and are accurate when needed. 

Gas detector calibration records should also be kept for every single instrument. A record for each device allows operators to identify any gas detectors that have needed excessive repairs or are prone to erratic readings, and to track the drift of sensors to determine when they need replacement. 

ISEA Statement on Validation of Operation For Direct Reading Portable Gas Monitors

Addressing Calibration Drift

When a gas detector’s reference point slowly changes, it is called calibration drift. This drift occurs to all sensors over time and leads to unreliable readings. Sensors that have experienced drift can usually still measure the quantity of gas present. However, they cannot convert the information into an accurate reading. Calibration checks with traceable gas concentrations will verify or update the device’s reference point. These checks should be completed often – daily in some instances.

Operators of gas detectors should also be aware of common causes of calibration drift to minimize potential drift. These include:

  • Degradation due to phosphate exposure
  • Degradation of phosphorus- or lead-containing components
  • Expected, gradual chemical degradation of sensors
  • Use of the detector in extreme environmental conditions. This includes extreme temperatures or humidity and high concentrations of certain airborne particulates
  • Exposure to high concentrations of target gases and vapors
  • Exposure of catalytic hot-bead LEL sensors to silicones, hydride gases, halogenated hydrocarbons, and sulfide gases
  • Exposure of electrochemical toxic gas sensors to solvent vapors or corrosive gases
  • Exposure to high amounts of vibration or shock that may affect electronic components and circuitry

The detector’s operability should be verified when it has been exposed to any of these conditions. It should also be verified if exposure is suspected. It’s also crucial to keep in mind that even though a gas detector sensor may appear unharmed, it could have damage that is not visible. 

Gas Detector Calibration Best Practices

There are a few basic rules when it comes to gas detector calibration, such as:

    • Follow the manufacturer’s guidelines. 
    • Use the correct tools for the job. 
    • Calibrate in environmental conditions that mimic the workplace.
    • Only used a non-expired certified traceable test gas. The test gas supplier should be able to provide a certificate of analysis for every test gas cylinder. Since the concentration of test gases does not stay stable forever, it is crucial not to use test gases that have passed their expiration date. 
  • Train operators how to properly perform a calibration. 

Operators may conduct a bump test, also called a function check, to confirm the detector’s alarms are functional. This test does not measure the device’s accuracy, but it should verify the alarm is working. 

Additionally, full calibration of the gas detector may not always be necessary. A calibration check can verify that the sensor and alarm are working properly when exposed to test gas. The device should first be “zeroed” to ensure results are accurate. And the concentration of test gas used should be high enough to trigger the alarm. If the reading is in the acceptable range, the calibration check has verified the accuracy. If the results are not in the acceptable range, a full calibration is necessary. Full calibration adjusts the reading to coincide with a known concentration of test gas. 

Workplace Safety

Many workplaces have combustible and toxic gases. Employees at these facilities have a higher risk of illness, injury, or death. The primary reason for gas detector calibration is to ensure worker safety. Proper calibration ensures that the detector will respond and alert workers to hazardous conditions. The OSHA guidelines are not formal regulations. However, they can serve to ensure proper calibration of gas detectors to maintain workplace safety. 

Calibration of MPS™ Sensors

Frequent calibration is often necessary for gas detectors, including NDIR and catalytic bead sensors. The Molecular Property Spectrometer™ (MPS™) can help organizations save money without sacrificing accuracy. These sensors have a longer life expectancy (up to ten years) than other types of gas detectors. They also do not require recalibration, which lowers the total cost of ownership of the MPS sensors. 

The MPS sensors are also extremely tolerant of environmental fluctuations and extremes. This represents a tremendous advantage over other gas detection technologies. Other methods can provide inaccurate readings even with small environmental changes and require frequent gas detector calibration. MPS sensors are a great tool to ensure that your workplace remains safe. Their accuracy means that everyone in the vicinity will know immediately if flammable or combustible gases are present. And accuracy is achieved even without recalibration. MPS sensors are the next generation of gas detection technology.