Abstract
Biosafety Level 3 (BL-3) laboratories are designed to prevent the escape of pathogenic microorganisms by operating at negative pressure so that if microorganisms become airborne, they remain within the laboratory. However, the authors are not aware of any published evidence or international guidance on the level of pressure differential required for BL-3 laboratories. This uncertainty was reflected in a survey of BL-3 laboratories in the United Kingdom where a range of pressure differentials between 30 and 100 Pascals (Pa) were found. In this paper, an attempt is made to address this issue. The authors have developed techniques to quantify the effectiveness of containment laboratories in preventing the egress of airborne microorganisms. A potassium iodide (KI) aerosol tracer method was adapted to measure the degree of containment in an experimental facility and in five working BL-3 laboratories. The level of laboratory containment was expressed as the laboratory protection factor (LPF). Using this technique, it was found that providing an anteroom increased the LPF by approximately one order of magnitude. No direct relationship was found between the magnitude of negative pressure and LPF. There was, however, a direct relationship between inflow velocity and LPF: A volumetric inflow of 10 m3/min into a laboratory through an anteroom gave a LPF of greater than 105. The KI aerosol tracer method offers a simple and appropriate means of validating the performance of BL-3 laboratories in terms of the LPF.