Advances in pharmaceutical research and development have allowed increasingly selective compounds to be synthesized, better targeting disease with minimal side effects. Often, therapeutic doses are on the order of micrograms. And this increased specificity means that the compounds have increased potency.

But greater potency typically comes with higher toxicity--operating and maintenance staff must be protected from exposure, and the environment must be protected from discharge into the environment. Facility design and attendant heating, ventilating, and cooling (HVAC) system decisions play a critical role.

Exposure Limits Defined

The Occupational Exposure Limit (OEL) concept is used to quantify the toxic effects of compounds on workers (Table I).

The American Conference of Governmental Industrial Hygienists (ACGIH) has historically published occupational exposure limit (OEL) values for many commonly-used industrial chemicals and termed them threshold limit values (TLVs). When the U.S. Occupational Safety and Health Administration (OSHA) was formed, the ACGIH TLVs were adopted and codified as workplace standards.

The OEL is the maximum concentration of a chemical (in air) to which most workers can be exposed for an 8-hour work day, 40-hour work week over a 40-year lifespan without significant adverse health effects. The OEL is expressed in milligrams of substance per cubic meter of air (mg/m³), parts per million (ppm) or even parts per billion (ppb). A higher OEL value means that a compound is more benign, so a worker may be exposed to more of this substance without future risk.

The OEL measures the health effects of long-term occupational exposure to a compound. Short-term exposure limit values (STELs) have also been developed to define the health effects of more acute occupational exposures. Permissible exposure limit (PEL) values are published in OSHA Standards 1910.1001 through 1052. Table I  identifies some sample permissible exposure limit values.