In our Gas Detection Applications Primer, we describe the notion of recommended and regulatory limits, as applied to toxic gases in the workplace. Discussed therein are the OSHA parameters of Permissible Exposure Limit, Action Level, and Ceiling Value.
If this “Action Level” is detected during initial monitoring of the occupancy in question, that is the trigger for increased industrial hygiene monitoring and initiation of worker medical surveillance. The Action Level is usually set at one-half the PEL, but there are exceptions such as formaldehyde. In this case, the PEL is 0.75 and the Action Level is 0.5 ppm.
OSHA PELs are listed in this handy table. Unfortunately, it is more difficult to locate a definitive list of Action Levels—presumably because they are almost always one-half the PEL. You will seldom go wrong using the “one-half” rule.
Sometimes, the Action Level is used as an alarm set point, but this is overkill in most cases. Remember that PELs are set up as eight-hour time-weighted averages. Even if your occupancy will frequently reach an instantaneous level near the PEL number, your eight-hour average may still be in compliance. If you are concerned that your occupancy might exceed the PEL as an eight-hour average, you might consider a data acquisition system whereby the eight-hour average is being continuously calculated, such as our Arc-Max®.
This would provide an alarm when the allowable eight-hour time-weighted average level is exceeded in less than eight hours. Depending our your instantaneous alarm set points, such an exposure would likely activate these alarms, as well.
If you need clarification on any of these matters, just contact us.