The toxicological effects of chemicals can manifest themselves in a number of ways. The results of exposure from some materials can be felt immediately such as watering of the eyes with lachrymators.

With other chemicals, there may be both immediate effects such as irritation and delayed effects such as pulmonary edema. With carcinogens there may be no symptoms yet effects are seen decades later. Effects of teratogens and mutagens are not seen until the next generation. With the thousands of chemicals that can be encountered and the different effects how does one go about determining what is a safe exposure?

OSHA Compliance – A Minimum Standard
Exposure concentrations and limits in air are typically given in parts per million (ppm), milligrams per cubic meter (mg/m3), or fibers/cm3 (fibers per cubic centimeter). Where additive exposure potential exists via absorption through the skin, a "[skin]" designation appears with the exposure limit.

The OSHA permissible exposure limits (PELs) (29 CFR 1910.1000) are typically the least restrictive exposure values and serve as a minimum performance standard in the United States. It should be noted that when PELs are established, it is a political process mixed with scientific evidence. Economic factors related to compliance are presented by industry groups and influence the final selection of exposure limits as a compromise value. OSHA limits may also lag behind new scientific literature as the entire political rulemaking process must be followed to make changes to a PEL. PELs are typically time-weighted average concentrations that must not be exceeded during any 8-hour workshift. Short term exposure limits (STEL) have been established for some materials and are usually measured over a 15-minute period. OSHA ceiling concentrations must not be exceeded during any part of the workday.

The American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs) are also expressed as time-weighted averages and short term limits. These are determined by ACGIH committees of experts in public health and related sciences through review of existing scientific literature. TLVs are based only on health factors and not subjected to a political process. The TLVs can more rapidly adapt to new scientific information than OSHA PELs. Most health and safety professionals we have known rely on the more conservative ACGIH TLVs as minimum protective standards for their clients.

However, TLVs and PELs are not available for most chemicals. The absence of an exposure limit does not mean a chemical is “safe”; it means that the chemical has not gone through the rigorous review and standards setting process. In the absence of exposure limits, the LD50 and LC50 along with physical parameters such as vapor pressure can help establish the risk of working with a chemical.

We have found the Poison Information Centers and Teratogen Information Service excellent sources of information when standard literature searches yield poor or equivocal results. The professional staff at these centers are willing to help, however, please let them know this is not an emergency and that you are willing to wait a few days for an answer. We would caution not to request assistance except when your efforts fail to find results by conventional means or of course when you have an actual exposure event.

There is a term “ALARA” taken from the nuclear industry. It stands for “as low as reasonably achievable.” This is a good mantra. Compliance with OSHA is a legal obligation; meeting ACGIH guidelines can help limit liability further. But reducing levels as low as one can using reasonable means makes good sense, further limits potential liability, and helps create a more pleasant and possibly more productive workplace.