What Exactly are Permissible Exposure Levels?

Alison Montgomery, CHST
API Safety Advisor, Owner Services Group

Worksite safety involves a great deal of terminology. Most of the terms have pretty obvious meanings. For example, “fall protection” is all about steps we’ll take to protect workers from falls.

Some terms aren’t quite as easily defined, so they can create confusion or misunderstanding among works. “Permissible Exposure Levels” is one of those terms. What exactly is an exposure, and what makes it permissible? And how can a worker or a safety professional determine levels?

In reality, the basic concepts behind Permissible Exposure Levels (or PELs) are very simple. An “exposure” refers to coming in contact with some kind of substance that is potentially harmful to humans. For example, an exposure might refer to touching or inhaling a solvent such as acetone. “Exposure levels” are a way of measuring just how much of the substance you’re exposed to over a certain period of time. And “permissible” refers to the acceptable levels that have been determined by industrial hygienists, safety organizations, or, most commonly, regulators such as OSHA.

Generally speaking, OSHA considers PELs to be how much exposure you can have while working during an eight-hour period. Whether the harmful substance is something in the air or something you might touch, the PEL says that your body can be in contact with only a certain amount of it over an eight-hour period before you have to take measures to reduce the exposure. (Note that OSHA’s PELs refer to an eight-hour period. If you’re at a jobsite where workers are on ten- or twelve-hour shifts, you’ll have to manipulate the PELs to reflect the specific situation.)

To help explain how PELs work, I can draw upon my experience overseeing safety in an automotive parts manufacturing facility. The workers soldered electronic parts to circuit boards then the boards would be cut apart by a machine. The employees would come into contact with dust containing the lead when cleaning clogged hoses and when cleaning the machine. Because lead is a material that can be harmful when it accumulates in the body, and because workers would be exposed to dust that contained lead, we had to observe OSHA’s PELs for lead..

While the dust was minimized through the use of an enclosed procedure and vacuums, there were times when workstations would have to be cleaned and the vacuum equipment would have to be disconnected.

OSHA’s PELs said we had to limit exposure to no more than 50 micrograms of lead over an eight-hour shift. Because our workers normally worked longer shifts, we decided to be extra careful, and set our own PEL at 30 micrograms over the entire shift.

To ensure we stayed below the PEL we measured lead exposure through blood tests that were performed during the annual fit test process. In addition, we mitigated the exposure to airborne lead by mandating respiratory protection for all the workers who performed soldering operations. We also had to determine the radius through which the lead dust could travel when the workstations were being serviced. We placed monitors in that radius to get an accurate measurement of how far the lead traveled. In selecting respiratory protection and filters for the vacuums, we had to identify filtration material that was capable of capturing the lead particles.

While that’s only one unique situation, it helps to explain what a safety professional has to consider when working with substances that have PELs. The first step is identifying exactly what types of substances are involved, and whether the process is enclosed or open. If the hazard cannot be engineered out of the process, it’s up to the safety professional to determine how best to monitor and mitigate the hazard.

Conditions that may affect the substances also need to be considered. If the work is being handled outdoors, the substances may behave differently in different temperatures and weather. Or, if other substances may interact with the first, the PEL may need to be adjusted.

Safety professionals also have to determine the type of training that will be needed, and which workers will need to be trained. It may even involve designating areas and setting rules that employees cannot enter those areas unless they’ve been trained in the specific hazard.

The key thing to remember is that the published PEL is just a starting point. Using that as a foundation, the safety professional has to consider all aspects of the hazard and how it may affect workers.

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