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Appl Environ Microbiol. 1974 October; 28(4): 647-650
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Modified Laminar Flow Biological Safety Cabinet

Department of Microbiology, Institute for Medical Research, Camden, New Jersey 08103

ABSTRACT

Tests are reported on a modified laminar flow biological safety cabinet in which the return air plenum that conducts air from the work area to the high efficiency particulate air filters is under negative pressure. Freon gas released inside the cabinet could not be detected outside by a freon gas detection method capable of detecting 10^-6 cc/s. When T3 bacteriophage was aerosolized 5 cm outside the front opening in 11 tests, no phage could be detected inside the cabinet with the motor-filter unit in operation. An average of 2.8 x 10⁵ plaque-forming units (PFU)/ft³ (ca. 0.028 m³) were detected with the motor-filter unit not in operation, a penetration of 0.0%. Aerosolization 5 cm inside the cabinet yielded an average of 10 PFU/ft³ outside the cabinet with the motor-filter unit in operation and an average of 4.1 x 10⁵ PFU/ft³ with the motor-filter unit not in operation, a penetration of 0.002%. These values are the same order of effectiveness as the positive-pressure laminar flow biological safety cabinets previously tested. The advantages of the negative-pressure return plenum design include: (i) assurance that if cracks or leaks develop in the plenum it will not lead to discharge of contaminated air into the laboratory; and (ii) the price is lower due to reduced manufacturing costs.