One of the most challenging issues related to today’s Level 3 biocontainment facilities is the BMBL* statement, “The laboratory shall be designed such that under failure conditions the airflow will not be reversed.” The ALN April 2010 column by Randy Kray and William Freeman entitled “Simple Airflow Strategies Provide You the Greatest Reliability” presented how ventilation control is a significant determinant in meeting the guideline. This article will therefore not expound much on the topic of volumetric offset versus active pressure control, but will focus on how to establish and execute a practical multifaceted plan to address the guideline statement on airflow reversals for both ABSL-3 and BSL-3 applications. It first addresses defining what is understood to be the intent of the guideline and then discusses how project teams can work towards complying with that intent.

Defining Intent – What does “no reversal of airflow” mean to your facility?
The initial step in meeting the guideline is to clearly define the intent of it, more specifically, what is considered “no reversal of airflow.” Misunderstandings and misinterpretations of the definition of an “airflow reversal” can cause project teams to invest significant resources to develop solutions that attempt to achieve more or less than what may be intended. The goal of the guideline is to maintain continuous airflow direction based on an assessment of clearly defined risks.

The first paragraph of the BMBL’s Introduction states that a “risk assessment is the process that enables the appropriate selection of microbiological practices, safety equipment, and facility safeguards that can prevent laboratory- associated infections.” The placement of that statement serves as a reminder to routinely assess risks so sound decisions can be made for standard operating procedures (SOPs) and facility features. Therefore, risk assessments should be the starting point for defining the intent of the guideline related to airflow reversals as well. Among the assessment questions related to airflow reversals are:

1. Where and how will infectious agents be handled by researchers?
2. What PPE will be used inside the ABSL-3/BSL-3 barrier?
3. What are the failure scenarios for which the secondary barrier will be challenged and should be prevented from having an airflow reversal?
4. How is containment achieved during this failure scenario?
5. How many and which doors must have a change of airflow direction for the room to be considered as having an airflow reversal?

For the sake of brevity, the last three questions will be explored for the purpose of showing an example of how one might define the intent of the BMBL airflow reversal statement. The challenge is to determine appropriate facility features that respond to a specific BSL-3 risk assessment, i.e., this may not apply to every ABSL-3/BSL-3 facility. If the greatest risk is determined to be the aerosolization of an infectious agent from a spill near a door in an ABSL-3 or BSL-3 room, then what facility features, PPEs, and SOPs are used to contain the agent? Since this article is about airflow reversals, facility features for this specific example should address, at a minimum, the last two questions. Those features may include fast-acting bioseal dampers, leakage areas around doors, and speed of fan and damper operating sequences.