Page 47 - Occupational Health & Safety, April 2018

Inhibitors, while not as destructive as poisons,
still have a negative effect
on the sensor. If combustible gases and inhibitors are present at the same time, the catalytic bead sensor may not detect the combustible gas.
with that heated bead, they instantly melt and head to the surface. Once these poisons encapsulate the catalytic bead, there is no way to remove them and the sensor must be replaced. Since this sensor now has a layer of the melted poison substance sur- rounding it, it is no longer able to burn any combustible gas that may come in contact with it and can no longer provide a reading.
If an instrument is not regularly cali- brated and bump tested, there would be no way to identify if it has been poisoned or not. This can put a user in a dangerous situ- ation as they could have a meter in a com- bustible environment that is not providing a reading due to the bead being blocked. If there is any thought that the LEL sen- sor may have been poisoned, it should be calibrated immediately to make sure it is in working order. If the sensor can read the calibration gas and provide a readout during this process, then it will be able to detect gas in the field. If the sensor is poi- soned, it will not be able to read the cali- bration gas applied and will give the user a failed calibration.
Inhibitors, while not as destructive as poisons, still have a negative effect on the sensor. If combustible gases and inhibitors are present at the same time, the catalytic bead sensor may not detect the combusti- ble gas. Inhibitors can desensitize the bead and may shorten its life span, but after a calibration and bump test, the sensor may still be in a usable state.
Some of the most common inhibitors would be halogenated compounds as well as anything containing astatine, bromine, fluorine, chlorine, and iodine. If an instru- ment has been exposed to any inhibitors, a calibration is recommended to make sure the instrument is still in working order. When the catalytic bead burns the gas from the calibration cylinder, it will also burn off some of the inhibiting material that may have been stuck on. If the bead is repeatedly
By starting each day with a calibration or bump test and calibrating your instrument any time you think it has come in contact with anything that may have a negative effect, you are ensuring that your instrument is in working order and will detect gas that may be present.
desensitized by inhibitors, or comes in con- tact with a large quantity of them, it may not recover, which results in a failed calibration.
Staying on the Safe Side
In some instances it may be obvious that the sensor was exposed to a poison or in- hibitor, but this might not always be the case. Many lubricants or silicone based products come in some form of spray that can bounce off of the surface it may be ap- plied to, and if standing too close, can easily come in contact with a personal gas detec- tor a user is wearing. A lot of these products also take some time to dry, releasing chem- icals and vapors in the process. Storage also has to be taken into consideration. Just be- cause a poison or inhibitor wasn’t applied directly to the instrument doesn’t mean that it may not have been exposed to some-
thing while in a tool box, storage locker, or anywhere else gas detection equipment may be stored.
Some of the most common poisons and inhibitors are listed above, but this does not limit the list to what has been stated here. By starting each day with a calibration or bump test and calibrating your instrument any time you think it has come in contact with anything that may have a negative ef- fect, you are ensuring that your instrument is in working order and will detect gas that may be present. If a meter was affected by a substance, a failed calibration will indicate this instrument is no longer in working or- der and will need attention.
Ryan Thompson serves as associate product manager at Industrial Scientific and can be reached at rthompson@indsci.com.
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APRIL 2018 | Occupational Health & Safety 41
COMING IN OH&S NEXT MONTH
Our May 2018 issue will preview the AIHce EXP2018 show in Philadelphia and will include an industrial hygiene section, along with respiratory protection, chemi- cal safety/SDS, combustible dust, and emergency eyewash & showers articles.