Someone pinch me! It is 2023, and I’m still teaching HAZMAT, Hot Work, and PRCS courses, where most students use direct-reading instruments daily. And yet, none of them have ever been trained on the LIMITATIONS of the brand/model of direct-reading instruments they use. There are dozens of reasons why this is what it is, but this oversight of the critical tool we use to make life-and-death decisions is unacceptable.
Back in the day, when I learned about the limitations of the meters we were using, I was floored and then scared to learn just how little I knew as a safety engineer. I also considered all the courses I had trained workers on PRCS entry and never mentioned these critical limitations. But I had a Plant Manager who grew up in one of the top chemical companies in the world, and he taught me the following when it comes to LEL readings on our direct-reading instruments…
It is a fact that OSHA has established that when an atmosphere is 10% of the chemical’s LEL, then it is a “hazardous atmosphere.” But why do we have to use OSHA’s definition/quantification? Why not remove all the “correction factors” from the process and use 2% as our LEL % limit for any work permit?
Almost everyone will agree that we want a reading of 0% on the LEL reading, so this idea that less than 10% is what we want is silly, setting up our supervisors for a severe error.
By establishing our LEL meter MAX reading to 2%, we get more objective about our safety expectations. It ensures that our supervisors will NOT send entrants into a PRCS over the actual 10% LEL of the atmosphere. The highest “Correction Factor” I have seen with a direct-reading meter is just less than 5.0, so even with that flammable vapor present in the atmosphere AND we have set our Max LEL meter reading at 2%, we will ensure all our entries will be into an atmosphere is LESS THAN OSHA’s 10% (e.g., Meter reads 2% times the 4.8 correction factor equals 9.6% which is less than 10%).
However,
- if the user of the meter is NOT knowledgeable of these LIMITATIONS of the LEL sensor and
- if the user of the meter is NOT knowledgeable of the correction factors that go with the sensor and
- if our program’s definition is 10% LEL
most entry supervisors will look at the meter reading, and as long as it is less than 10%, they will authorize entry into a hazardous atmosphere.
For example, the meter reading is 9% LEL, and since that is less than 10%, they will think the LEL is less than OSHA’s 10% limit. If the correction calculation for the flammable gas/vapor is 4.8, the atmosphere they authorize entry into is 43% of the LEL (nearly halfway to achieving an explosive atmosphere).
If we want to keep our PRCS program definition of a Hazardous Atmosphere, as it relates to a flammable atmosphere, at 10%, then it will be incumbent on us to train the user(s) of our brand/model of the direct reading instrument(s) on the proper use of its “correction factors” for the LEL sensor. This means the meter user will always have access to these correction factors to adequately determine the REAL LEL% of the atmosphere being sampled.
TRUST me; it is easier to declare 2% as the MAXIMUM reading on the meter. Any reading over 2% requires a safety team member who is fully knowledgeable of the limitations of the meter(s) being used to approve the permit AFTER they understand the actual atmosphere.
PLEASE see my other articles on this safety-critical topic
Improper direct-reading instrument sampling tube leads to fatal explosion (2023)
Your 4-gas direct-reading meter has been lying to you (2018)
One MAJOR flaw in the use of Combustible Gas meters that ALL users should know (2011)
