The Efficiency of HEPA Filters in the Air-Handling System of a Bio-Containment Laboratory in India

Abstract

The High Security Animal Disease Laboratory (HSADL) in Bhopal, India is a BSL-4 laboratory that was constructed following the Labystad (The Netherlands) model and was commissioned in 1997 as a bio-containment facility to undertake research and diagnostic work on exotic and emerging diseases of animals in the country. The laboratory's air-handling system is comprised of 23 air-handling units (AHUs) with 97 HEPA filters (Anfilco, India) fitted in 92 filter housings. Preventing environmental contamination is achieved by maintaining graded negative pressure ranging between −50 to −200 Pascals. This paper discusses the efficiency of the HEPA filters following the dioctylphthalate (DOP) testing carried out over a decade-long period. Out of the 81 (83.5%) filters replaced during this period, HEPA filters of 59 (72.83%) housings were replaced once; of 17 housings (20.98%) were replaced twice, and of 6 housings (7.4%) were replaced three times. Major reasons for the replacement of these filters include blockage (48.18%) and lowered efficiency (51.85%) of the filter medium. The majority of the filter changes at HSADL can be attributed to the routine ageing of the filters, resulting in the degraded mechanical strength of the filter medium or choking due to aerosols and dust. Some areas of the laboratory encountered a higher rate of filter change and the reasons thereof are discussed. These observations regarding HEPA filter efficiency in AHUs are probably the first in a tropical environment. The possible roles of factors such as the availability of a dense tree canopy in the direction of the air flow, the close location of the lab to a large water body, and the lab's distance from the dusty highways in the longevity of this laboratory's HEPA filters are also discussed. This study re-emphasizes the need for regular monitoring of the HEPA filter function in the AHUs and their prompt replacement when damaged to ensure effective bio-containment.