A brief discussion on the ventilation of toxic substances. Since health effects of chemicals occur at air concentrations well below the lower explosive limits of solvents and gases, ventilation to prevent health effects will also prevent a buildup of vapours which could cause fires or explode. There are two types of ventilation: dilution ventilation involves bringing in clean air to dilute contaminated air, then exhausting the diluted air to the outside via exhaust fans. Local exhaust ventilation involves trapping the contaminants at source before they get into the air bein inhaled. References.