There are few air contaminant levels specifically established for children in schools. Human exposure guidelines for a number of air pollutants have, however, been established in regulations or recommended for other environments by various governmental agencies and professional organizations. Differences between guidelines usually stem from the assumptions about the population each guideline is intended to protect. For example, air contaminant limits for the industrial workplace are comparatively high since they are intended to protect a relatively healthy, adult workforce, are not intended to protect the more sensitive individuals, and assume little or no exposure to the contaminant beyond the normal 40-hour work week.

The Occupational Safety and Health Administration (OSHA) regulates workplace exposure to many laboratory chemicals through the use of Permissible Exposure Limits (PELs). The National Institute for Occupational Safety and Health (NIOSH) performs health effects research and studies, then makes recommendations to OSHA for new regulations based on their work. The OSHA PELs and NIOSH recommendations are contained in Department of Health and Human Services (NIOSH) Publication no. 90-117, "Pocket Guide to Chemical Hazards," available from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402.

The American Conference of Governmental Industrial Hygienists (ACGIH) annually publishes a list of Threshold Limit Values (TLVs) to be used as guidelines for the control of potential health hazards in the workplace, including those found in laboratories. The original OSHA PELs were based on the 1968 list of TLVs. TLV booklets are available from ACGIH, Technical Information Office, 1339 Kemper Meadow Drive, Cincinnati, OH 45240.

Other organizations and regulatory bodies have developed approaches for assessing non-industrial workplace exposures.

These are summarized below.

• ASHRAE Standard 62-1989 summarizes IAQ exposure guidelines and applicable standards used in the U.S. and Canada and consensus guidelines published by the World Health Organization. Appendix C of this standard recommends that the TLVs be divided by 10 before using them to evaluate IAQ exposures. Information regarding ASHRAE standards is available from ASHRAE, 1791 Tullie Circle, N.E., Atlanta, GA 30329.

• Many states are developing air toxics regulations or guidelines. Most of these states are applying safety factors to workplace exposure limits to develop ambient (outdoor) exposure limits. The safety factors used vary from state to state and range in magnitude from 42 to 100. These limits are designed to protect the more susceptible members of the general population (asthmatics, etc.) and, therefore, may be more applicable for evaluating the indoor environment where protection of similar populations is desired. However, the scientific basis for the safety factor must be understood and matched with the toxic hazard presented by each chemical.