Share thisIn the previous column, we reviewed some basic principles and features found in the Biosafety Microbiological and Biomedical Laboratories (BMBL) 5th Edition for BSL-3 and ABSL-3 containment design. We described the fundamental need for risk assessment for a given laboratory or animal research program in order to effectively design the BSL-3 or ABSL-3 facility to meet the specific requirements of that program.We also highlighted the new Appendix D, Agriculture Pathogen Biosafety section, which provides excellent guidance on requirements for working with Pathogens of Veterinary Significance in a complimentary relationship to the main body of requirements in the BMBL. We also discussed directional airflow—the new language found in the 5th Edition and the challenge interpreting its intent into facility design. We will go further into this subject in this column.
The question we will review here is simple to state but not so simple to answer: how do we best meet the BMBL 5th Edition requirement which states that, “the laboratory shall be designed such that under failure conditions the airflow will not be reversed?”
Redundancy and Reliability
To understanding this problem, it is important to begin by differentiating between the concepts of reliability and redundancy. To prevent the reversal of airflow is a system reliability requirement. It does not necessarily dictate the need for redundancy. In fact, redundancy can make reliability more difficult if it is not managed carefully. In principle, reliability is best achieved through simplicity. Simple here means to design with straightforward logic and relationships, fewer moving parts, and fewer things to break or drift out of proper alignment. Redundancy means more failure scenarios. It creates more parts and more complex relationships that must be configured and maintained properly to work as intended.
A Simple Model
Using this dictate, the simplest way that we can achieve airflow from area of least hazard to highest hazard will be to supply all the air required into a clean corridor (with no exhaust in that space), exhaust all the air via the BSL-3 laboratory (without any additional supply), and design an ante room between these zones that allows the transfer of the air from corridor to lab efficiently. In this way, we have provided a fully compliant BSL-3 laboratory that has no means to reverse the airflow. So long as there is power to move air, there will be proper airflow of some measure. Loss of power and motive force to move the air will make the rooms go neutral but not reverse airflow. Such an arrangement, with the right transfer methods across the ante room barriers, would be ideal for a basic BSL-3 laboratory. It would be simple to construct, to balance the airflow, and maintain in balance.
In practice though, most BSL-3 laboratories cannot be solved this simply. The ventilation requirements of laboratories and animal spaces are typically greater than can be achieved by just air transfer across barriers. Therefore, we have to provide both supply and exhaust air in most rooms. This creates a system that is not inherently as fail-safe as our simple example above. In addition, BSL-3 laboratories are often more complex than the one room laboratory example in terms of the relationship of spaces. We have to design systems that respond to dynamic relationships of spaces because of variables such as the opening and closing of doors, loading of filters, and changes over time to the leakage characteristics of rooms. Ventilation systems and airflow control are more complex in response to these requirements.