Walk-in type LEPT Series fume hoods intended to provide a standard for selection, installation, usage and maintenance of the laboratory. The exposure control system is explosion-proof in the sense of having all potential ignition sources located outside the cabinet. However, if the vapors can escape from the freezer and sink to floor-level then the potential for fire or explosion continues to exist if the vapors come in contact with other sources of heat or flame which are inherent in most laboratories.