Applied Biosafety

To determine the effectiveness and limitations of ultraviolet (UV) germicidal lamps in biosafety cabinets and pass-boxes, with particular reference to anthrax spores.

An estimated 50 colony forming units (CFUs) of spores of the Sterne strain of Bacillus anthracis were distributed on blood agar plates and on smooth and rough plastic surfaces, glass slides, galvanized metal strips, squares of writing paper, nitrocellulose/cellulose acetate strips, and membrane filters. After drying these were exposed in triplicate to the UV sources of a Class 2 biosafety cabinet and a biosafety level (BSL) 3 pass-box for various time periods. Viable B. anthracis could not be recovered from hard surfaces at 15 minutes (the shortest time period tested) when fully exposed to UV at intensities of ≥ 3.8 W/m² (the lowest intensity tested) in a Class 2 biosafety cabinet and a BSL3 pass-box. However, the penetrating ability of the UV was found to be extremely limited with even the microstructural elements of nitrocellulose or similar membranes able to substantially shield the spores. The UV failed totally to penetrate thin (66 μm) paper or Petri dish plastic, although it did penetrate plastic sandwich wrap.

The UV from germicidal lamps in biosafety cabinets and pass-boxes is rapidly sporicidal for fully exposed anthrax spores on hard surfaces but is readily nullified by the slightest obstacle to direct exposure.

The results fill a major information gap for those devising or following protocols for decontamination of items and materials in biosafety cabinets and pass-boxes. Such protocols need to be written around a full comprehension of the data presented here.