Biology ETDs

Publication Date



An Envirco Model DF-400 laminar down flow hood with an exhaust HEPA filter adaptation was tested for its efficiency by using Bacillus subtilis var. niger as an indicator organism. The experimental emphasis was on the bacterial spore penetration of the frontal barrier and of the exhaust system. Interior and exterior challenges were made. The interior challenge utilized two heights and progressed from the front of the hood to the rear. Bacterial migration on the hood surface, surface impingement, ambient air conditions, and exhaust air were checked. All ambient air sampling was done with Andersen samplers. The exterior challenge consisted of producing an aerosol at three heights and at two depths. The results were obtained on settling plates as were all studies within the work area. The results indicate the exhaust system is very efficient with a drop of at least 7 orders in magnitude of bacteria across the filter. The exterior challenge possibly showed an extremely small amount of organism penetration but the number of organisms was not significant. However, the interior challenge penetrated the frontal barrier when the aerosol was released within 8 inches of the front of the cabinet near the work surface and within 12 inches at the hood eyelid height. This is a function of the turbulence at the eyelid. Practical application experiments indicate these distances contain a safety factor.



Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Committee Member (Chair)

John Wm. Beakley

Second Committee Member

Gordon Verle Johnson

Third Committee Member

Bruce David West

Included in

Biology Commons