By Safety Management Group
Workers in many industries perform their tasks with and around a wide variety of chemicals. Each of those chemicals may pose some level of danger to the workers’ well-being, depending upon how closely and how long they come in contact. But exactly how much exposure is too much?
OSHA answers that question through what are known as Permissible Exposure Limits (or, more familiarly, PELs). PELs are legal limits for the degree to which workers may be exposed to chemicals and other hazards (such as noise) without suffering harm.
PELs are normally expressed in what are known as time-weighted averages (TWA), which describes the average exposure over a set period. In most cases, the TWA reflects a standard eight-hour shift, based upon a 40-hour workweek. In some cases, the chemical may also have short-term exposure limits (STELs) or ceiling limits. As the terms imply, those are the maximum levels to which workers may be exposed, even for a very short period of time.
When TWAs are used, it’s important to remember that they are averages. It’s entirely possible that a worker may be exposed to significantly higher levels of a chemical for a period of time during the eight hours. Those situations involve another term — the excursion limit — that normally describes situations in which workers are exposed to more than three times but less than five times the TWA PEL for no more than a total of 30 minutes during a shift.
If a worker is exposed to more of the chemical than allowed by the STEL or excursion limit, he is required to be completely removed from the hazard for at least an hour.
Another measurement created by the National Institute for Occupational Safety and Health is a level of a substance that is considered to be immediately dangerous to life or health (IDLH). NIOSH describes IDLH as an exposure “that is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment.”
The problem with PELs
OSHA is responsible for determining PELs. Shortly after the agency was established in 1970, it set levels for nearly 500 chemicals. Unfortunately, legal disputes about the rulemaking process have kept OSHA from adopting any new PELs since then, and the agency has been unable to update its original PELs to reflect newer scientific data. In fact, OSHA has only been able to update fewer than three dozen of the PELs.
That creates two concerns for workers. First, PELs exist for only about 500 of the thousands of chemicals that may be found in American workplaces. Second, the vast majority of the PELs that do exist are nearly 50 years old. That has led many occupational safety experts to express concerns that the PELs provide inadequate protection of worker health and safety.
How can employers and safety professionals contend with that perceived shortfall? OSHA has suggested that employers use alternative exposure limits developed by other organizations, because those alternative measures generally allow less exposure than the PELs.
RELs, TLVs, and BELs
One of the other measures is RELs, or Recommended Exposure Limits, developed by NIOSH. That agency evaluates all of the most current evidence about the chemical’s properties and effects upon workers before issuing RELs. Details of RELs appear in publications such as the well-known NIOSH Pocket Guide to Chemical Hazards.
A private scientific organization known as ACGIH (the American Conference of Governmental Industrial Hygienists) has developed a pair of health-based limits that may be useful to employers, although they should not be approached as legal standards for workplace safety. The first, Threshold Limit Values (TLVs), identifies the airborne concentrations of chemicals to which workers can be exposed on a daily basis without harmful effects. OSHA requires TLVs to be included on safety data sheets for chemicals.
The second measure, Biological Exposure Indices (BEIs), considers how much of the chemical may have been accumulated in the worker’s body, such as what can be detected in blood and urine. However, ACGIH does not believe these measures should be used for standards without considering other risk management-related factors such as technical and economic information.
Key information
The NIOSH Pocket Guide provides well-organized information for nearly 700 common chemicals or types of substances that are commonly used on jobsites. It uses a table format to list the name of each chemical or substance, as well as its:
– chemical structure or formula
– Chemical Abstracts Service registry number (CAS number)
– Registry of Toxic Effects of Chemical Substances number (RTECS number)
– U.S. Department of Transportation (DOT) identification and guide numbers
– trade names and known synonyms for the chemical or substance
– factors for converting measurements
– NIOSH Recommended Exposure Limits (RELs), using a time-weighted average concentration
– the short-term exposure limit (STEL)
By using the OSHA PEL (when available) as a starting point, and the NIOSH Pocket Guide as a reference, employers should be able to make reasonable decisions about the amount of exposure that’s acceptable on their worksites.
