Ventilation systems have to be balanced to work right. Sometimes, a change is made which affects the ventilation system and it stops working well. Sometimes, the system was poorly designed.

There are two kinds of ventilation:
* General ventilation (for moving the air in a room)
* Local exhaust system (to exhaust air with a lot of contaminants, usually using a ventilation hood)

One of the most common air quality problems is when buildings don't have good general ventilation systems. When people have symptoms in the building but feel fine when they're away from it, it's called Sick Building Syndrome. Common problems are:

  • The intake may be near a delivery dock so it's sucking in diesel fumes.
  • The intake may be right next to the exhaust, so it sucks the exhausted air back in.
  • A smoking area may not be exhausted directly outside, so the smoke is re-circulated throughout the building.
  • The HVAC (heating, ventilation, and air conditioning) may not be maintained regularly, so air filters are not clean and pools of water grow mold and bacteria.
  • The boss may save money on heating or air conditioning by not bringing in enough outside fresh air.

Many of the resources on ventilation and air quality are written for union members who have rights to inspect their workplaces, survey their co-workers about symptoms, ask questions without being intimidated, and bosses can't refuse to give information. If you don’t have a union, the materials can still help to understand the problem.