Fume hood face velocity directly affects the laboratory's energy efficiency. Higher face velocities increase exhaust air-flow rates and consequently increase the volume of conditioned air expelled, requiring more fan energy. In other words, reducing the fume hood face velocity increases a laboratory's energy efficiency.
The safest fume hood face velocity has been the subject of numerous studies and evaluations that have produced the following two criteria:
·Face velocities in the 60 to 100 fpm range provide acceptable and safe hood operating conditions.
·Room air patterns can account for at least 50 percent of unsafe hood performance. [Saunders, 1993; Lyons et al., 1990]
These data were reviewed and published in 1982 by the American Conference of Governmental Industrial Hygienists (ACGIH). This endorsement by a society of health professionals, of the criteria, which are substantiated by excellent research, made a definitive statement regarding hood safety and face velocities. Some fume hood manufacturers' catalogs still reflect parameters as outlined in SAMA Standard LF 10-1980, where so-called class A, B, and C hoods are represented with face velocities up to 150 fpm. In view of more current data, these A, B, and C classifications and their implied face velocities should be ignored. Relying upon this increased face velocity rather than considering hood and room ventilation design wastes energy. [Saunders, 1993]
Face velocity—a historical review
Measured face velocity