Depending on the industry, workers may be at risk from exposure to tobacco smoke, carbon monoxide, allergens, bacteria, viruses, and chemicals that build up indoors.

Workers may also be exposed to airborne contaminants on the job such as dusts, welding fumes, gases, solvent vapors and mists. 

If you aren't sure, ask yourself: 
 Do health symptoms improve when you leave the building? 
 Do they return when you come back into the building?

Inspecting the heating, air conditioning and ventilation systems is an important step, as many of indoor air problems involve those systems. The inspection looks for potential indoor problem sources, as well as outdoor sources that may be brought indoors via the ventilation system.