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Gas Meter Calibration Requirements - OSHA and Technical Considerations

Why do gas monitors need to be calibrated? Hasn't technology advanced enough that calibration requirements are overkill? These questions are common. We hope to convince you that calibration is essential (and required, of course) for the safety of any confined space entry program.

Technical Calibration Considerations

Typically, it is thought that OSHA requirements drive the push to frequently calibrate gas meters. In fact, however, it is the technology used in gas meter sensors that necessitate the need for calibration.

All four sensors in a typical confined space gas detector - Oxygen, Combustible, Hydrogen Sulfide, and Carbon Monoxide - have limitations that contribute to their decline in accuracy.

Electrochemical sensors, typically H2S and CO, are certainly the most durable of the four sensors. However, these sensors can be compromised by dirty filters, exposure to organic solvents and alcohols, and exposure to methanol. These sensors also just wear out with age.

Oxygen sensors (typically fuel cell type sensors) can develop slow response times over a short period of time. They also age faster than other sensors. On occasion, the electrolyte in them can leak.

Combustible sensors are particularly prone to being poisoned by high levels of explosive gases (like butane) or a number of other substances. Once poisoned, they are inaccurate and may malfunction all together. They also age over a short period of time.

Any of these issues mentioned above will put a gas monitor "out of" calibration. For example, as sensors age, they experience what is called calibration drift. In other words, they become inaccurate. I'll have more on calibration drift in the next section.

In addition to all of the above, it is important to note that calibration can be compromised if the sensors or instrument are subject to a fall or other sort of impact. It is possible to have just calibrated an instrument...drop it...and it be no longer "in calibration".

Finally, and importantly, sensors also age whether they are used or not. It does not matter if you've stored your meter away for 6 months and never used it. The sensors still age and drift.

OSHA Calibration Considerations

OSHA, in their Calibrating and Testing Direct-Reading Portable Gas Monitors Bulletin, is very clear why they require gas meter calibration. They rightly point out that, "exposure to hazardous levels of toxic gases or to an oxygen-deficient atmosphere...can cause workers to suffer serious injuries or illness, and even death. Flammable gas explosions are often catastrophic, resulting in worker injuries and death, or destruction of property."

Calibrations prevent injury and death. This is a legitimate and serious concern. Lives are lost every year due to gas monitors that are not giving accurate readings.

OSHA's explanation for why inaccuracies in meter readings occur has nothing to do with a desire to implement heavy handed rules and regulations. It has everything to do with, you guessed it, technical considerations.

All sensors lose accuracy over time. The amount they lose and how long it takes varies. This loss of accuracy causes calibration drift. This means that the reference points for the measured gases established at the prior calibration are no longer valid. Therefore, the readout is no longer accurate.

The amount of calibration drift can depend on many environmental issues as well as sensor age. OSHA actually cites many causes of calibration drift. Here are a few:

  • Gradual chemical degradation of sensors
  • Use in extreme environmental conditions, such as high/low temperature and humidity
  • High levels of airborne particulates
  • Exposure to high concentrations of target gases and vapors
  • Handling and jostling of instrument that causes vibration or shock to circuitry

Given the real problem of calibration drift, a technical feature of any gas monitor, OSHA requires regular calibration. It's the only way to be certain the technology is working properly.


So the requirement to calibrate frequently, is wholly due to the limitations of the technology. It's not heavy handed regulation. Such requirements will and do save lives.

A quick note on bump testing: for all of the above reasons, OSHA and most manufacturers recommend a bump test before each use. This can be as simple as exposing the sensors to calibration gas and confirming that each responds.

So what should you do? Send your meters back to us for regular calibrations and bump test your meters before each use. A perfect bump test gas solution is just a click away.


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