Dilution ventilation relies on adequate circulation of fresh air in the room to dilute the contaminant concentration. This type of ventilation has a number of limitations:
- workers close to the air contaminant’s source may be exposed to high, localized concentrations of the contaminant,
- dilution ventilation systems are affected by weather conditions (doors or windows are kept open or closed depending on the temperature) and the movement of objects and people in a room, and
- if the rate of contaminant generation increases, the dilution supplied may be inadequate.
Given these limitations, such systems are usually not recommended for contaminants that are highly or moderately toxic.