The best way to prevent or reduce exposure to airborne substances is to control their escape into the work environment by the use of laboratory hoods and other ventilation systems.
The two basic types of laboratory ventilation are general dilution and local exhaust ventilation.
A. General Dilution Ventilation (GDV)
General dilution ventilation refers to the quantity and quality of air supplied, for example, exchanging indoor room air with outdoor air. Laboratory air should be replaced continuously, approximately 6 to 12 air changes per hour, so that the concentration of air contaminants are continuously diluted.
General dilution ventilation should NOT BE RELIED ON FOR PROTECTION FROM TOXIC SUBSTANCES RELEASED INTO THE LABORATORY. It provides only modest protection against toxic gases, vapors, aerosols, and dusts. It is an inefficient way to control highly toxic contaminants because of the amount of air exchange necessary to achieve dilute concentrations within acceptable ranges.
Laboratory air should not be recycled. GDV is intended to increase the comfort of the laboratory environment and to serve as a source of air-flow through the ventilation system and through dedicated systems, such as fumehoods.
Typical uses for GDV include:
B. Local Exhaust Ventilation (LEV)
Local Exhaust Ventilation is a system designed to exhaust contaminants captured near their source without allowing them to escape and disperse into the laboratory atmosphere. Laboratory hoods use LEV to prevent harmful dusts, mists, fumes as well as toxic gases and vapors from entering the laboratory.
Laboratory hoods offer other types of protection as well. A chemical reaction system located within a hood, with the hood sash correctly lowered, places a physical barrier between the worker and the chemical reaction system. This physical barrier will provide protection from hazards such as chemical splashes, spills, sprays, fires and minor explosions from an uncontrolled reaction.
C. Other Local Ventilation Devices
Ventilated storage cabinets, canopy hoods, snorkels and other such devices should be provided as needed. Each canopy hood and snorkel should have a separate exhaust duct.