Occupational exposures in the work place are evaluated by comparing the airborne concentrations of regulated substances to the most recent Federal Occupational Safety & Health Administration (OSHA) Permissible Exposure Limits (PELs) and the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limits Values (TLVs). PEL's/TLV's are time-weighted average concentrations for a normal 8-hour workday or 40-hour work week to which nearly all workers may be repeatedly exposed, day after day, without adverse effects.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has suggested the use of more stringent guidelines for indoor air quality based largely on the National Ambient Air Quality (NAAQ) Standards adopted by the Federal Environmental Protection Agency (EPA) for outdoor air. These guidelines are based on concentrations at which at least "80%" of building occupants normally do not express dissatisfaction due to unsatisfactory indoor air quality. These guidelines do not address the comfort levels of hypersensitive individuals or those with existing medical conditions.
Recent studies conducted by the National Institute for Occupational Safety and Health (NIOSH) indicate over "50%" of indoor air quality complaints originate due to ventilation problems in the work place. ASHRAE Standard 62-1989 recommends a ventilation supply rate of 20 cubic feet per minute of outdoor air, per person, for satisfactory indoor air quality in the work place. The quantity of outdoor air can be determined by comparing carbon dioxide levels within the space to outdoor concentrations. Maximum guideline for maximum indoor carbon dioxide concentrations vary between leading indoor air quality organizations and federal, state and local concerns. The OSHA permissible exposure limit (based on an 8-hour time-weighted average) for carbon dioxide is 5000 ppm (parts per million), whereas the American Society of Heating, Refrigerating & Air Conditioning Engineers (ASHRAE) recommends a maximum concentration of 1000 ppm and the Commonwealth of Massachusetts, Department of Public Health and Workforce Development (DLWD) recommend levels not to exceed 800 ppm. The current standards for the contaminants evaluated are as follows:
| OSHA | ACGIH* | ASHRAE* | MA DPH/DLWD* | |
| Cartbon Monoxide | 50 ppm | 25 ppm | 9 ppm (8 hrs) | 9 ppm |
| Carbon Dioxide | 5,000 ppm | 5,000 ppm | 1,000 ppm | 800 ppm |
PPM = Parts per million
* recommended standard