Share thisFor basic and enhanced BSL-3 and ABSL-3 facilities, the CDC/NIH guideline, Biosafety in Microbiological and Biomedical Laboratories (BMBL), states that the spaces be sealed. This lead to confusion and effort beyond what is can lead to confusion and effort beyond what is required for biosafety.
The BMBL does not require an objective measure for the sealing of BSL-3 and ABSL-3 facilities, thus allowing each institution to determine their requirements based on risk assessment and planned use of the facility. When examined, even terms like airtight and gastight, unless specifically defined for the application, become subjective when questions like “what pressure differential,” “what gas,” and “how tight” are raised.
It is important to note that the generally accepted criteria for testing rooms that act as primary containment, such as the “pressure decay test” defined in the USDA Agricultural Research Service Facility Design Standards, 242.1M, does not provide 100% airtight construction. “Pressure decay” implies “leakage over time” at certain pressures. It is also important to point out that the construction technology, cost, and effort required to design, build and maintain a true “pressure decay tested barrier” far exceeds the requirements of most BSL-3 and ABSL-3 spaces. We as owners, architects, engineers, and constructors often make it much harder and more costly by trying to create containment barriers that are greater than needed to safely contain the biohazards. Often, the lack of knowledge of the fundamental nature and purpose of the BSL-3 or ABSL-3 facility containment barrier is the culprit.
The BSL-3 and ABSL-3 facility containment barrier is (almost always) the secondary containment barrier. It is allowed to have openings such as space below and along the sides of doors to allow directional airflow to come into the room, ducts to allow supply and exhaust air to be moved into and out of the space (these openings may or may not have HEPA filters), and openings for measurement of airflow or to provide devices to indicate directional airflow. As one understands that unfiltered openings are allowed to occur in the barrier, one also understands that the sealing of the room has little impact on biosafety. The attempt to keep microorganisms in the room (if they were actually outside of the primary containment) by sealing the walls would be futile. If microorganisms were able to pass out of the room through the walls, they could more easily pass out of the room through the intended openings described above.