Share thisThe last few columns discussed planning issues related to the design and construction of biocontainment facilities. The next few columns will discuss some technical issues and the rationale behind the technical issue so that good judgment can be made in the application of technical criteria. This column will focus on HEPA filtration of the heating, ventilating and air-conditioning (HVAC) system of a BSL-3 laboratory or animal facility. It seems that HEPA filtration has become an arbitrary decision for BSL-3 laboratories and animal facilities; however, there should be clear rationale for their use. Without this, the addition of HEPA filtration unnecessarily increases operating and maintenance costs without concurrent benefits.
Filtration considerations for exhaust air from a BSL-3 laboratory
The CDC/NIH Guideline Biosafety in Microbiological and Biomedical Laboratories (BMBL) states that for BSL-3 laboratories, “A ducted exhaust air ventilation system is provided. This system creates directional airflow that draws air from ‘clean’ areas into the laboratory toward ‘contaminated’ areas. The exhaust air is not recirculated to any other area of the building. Filtration and other treatments of the exhaust air are not required, but may be considered based on site requirements and specific agent manipulations and use conditions. The outside exhaust must be dispersed away from occupied areas and air intakes or the exhaust must be HEPA filtered.” Clearly, basic BSL-3 laboratories that follow the procedures and practices outlined in the BMBL do not automatically have to be HEPA-filtered.
For ABSL-3 animal areas, the BMBL states that, “Ventilation should be provided in accordance with criteria from the Guide for the Care and Use of Laboratory Animals, latest edition. A ducted exhaust air ventilation system is provided. This system creates directional airflow which draws air into the laboratory from “clean” areas and toward “contaminated” areas. The exhaust air is not recirculated to any other area of the building. Filtration and other treatments of the exhaust air may not be required, but should be considered based on site requirements, and specific agent manipulations and use conditions. The exhaust must be dispersed away from occupied areas and air intakes, or the exhaust must be HEPA-filtered.” Again, basic ABSL-3 animal facilities that follow the procedures and practices outlined in the BMBL do not automatically have to be HEPA-filtered.
If the air exhausted from the room does not automatically have to be HEPA filtered, when should HEPA filtration be considered? Examples include:
• In general, the exhaust from BSL-3 laboratories is expected to be dispersed above the laboratory in a manner that allows dilution and dispersion away from the building. However, at times, particularly in old facilities, this may nor be possible. If there is a significant chance that exhaust from the BSL-3 laboratory or animal facility could re-enter the facility through windows or air intake louvers, HEPA filtration should be provided in the exhaust stream.
• Some agent summary statements in the BMBL recommend that laboratories working with specific agents (such as VEE) have the exhaust air HEPA-filtered.
• The risk assessment of some agents that are easily transmitted with a low infectious dose such as Q Fever or LCMV used in an animal facility may determine that the facility should have exhaust HEPA filtration.
• Uses of BSL-3 agents in a manner with a high probability of generating an aerosol that could escape primary containment may warrant HEPA filtration.
• Uses of agents in animal species or equipment that has limited primary containment available may generate a risk that would need exhaust HEPA filtration for mitigation.
• High environmental consequence such as highly pathogenic avian influenza may require HEPA filtration as determined by the permitting agency.
• The risk assessment, if large quantities of agents are used with the potential to escape outside of a closed system, may suggest exhaust HEPA filtration.