Containment testing for occupied and unoccupied laboratory chemical hoods.

Containment of hazards in a laboratory chemical hood is based on the principle that air drawn through the face area of the hood is sufficient to overcome the many challenges at or near the opening. Challenges to overcome include, but are not limited to, air velocities near the hood, movement of the researcher, people walking past the hood, location of equipment inside the hood, size of the sash opening, and the shape and configuration of entrance conditions. To overcome these challenges, a sufficient face velocity must be maintained. Determining that proper face velocity for a given hood should be resolved by the system designer, facility safety officer, and researcher with these and other issues in mind. This research tests for containment at 100 feet per minute (fpm) face velocity on occupied hoods and tests the same hoods for containment at the reduced velocity of 60 fpm when unoccupied. Three laboratory chemical hoods of different sizes with several sash positions are used. The test results show that under ideal conditions in a test laboratory, an unoccupied hood (without a manikin) at 60 fpm contains as good as, if not better than, an occupied hood (with a manikin) at 100 fpm, as measured by the tracer gas tests specified in ANSI/ASHRAE 110-1995, Method of Testing Performance of Laboratory Fume Hoods (ASHRAE 1995). Further testing is needed to determine if this relationship is the same under conditions of actual use, i.e., cluttered hoods and presence of cross-drafts