BSL-3,Engineering Controls

When you think about BSL-3 and higher biocontainment laboratories, working with dangerous pathogens in cabinets or with infected animals, it is understood that, “these are no ordinary laboratories.” At least partially when you make this statement, you are likely assuming that the physical property of these rooms, their containment barriers, are critically important for their safe operation; they must be constructed in special ways to prevent the escape of pathogens outside the laboratory and handle the harsh treatment these spaces endure in their operations. Depending on your frame of reference, this may mean anything from well-built gypsum board rooms all the way to welded steel submarine-like rooms, or something in between such as panel construction, masonry, or concrete barrier systems, to name the most common barrier systems.

How do you choose the right system for your application and to what specifications must it perform to? All of these systems and methods have been successfully and appropriately used to construct high containment laboratories. Cost and performance vary a great deal between these system options and it is well worth understanding the factors to make the right choice for your facility design.

Containment barriers have three key performance criteria that form the basis of their selection process:

1. Containment—preventing the escape of airborne biological hazards.
2. Enabling effective and safe fumigation procedures to decontaminate the room.
3. Enabling effective cleaning of the barrier.

Preventing Pathogen Escape
Emotionally and politically, preventing the escape of dangerous pathogens may be a key element of how you see the barrier’s role. However, from a risk perspective, this containment function is not the primary driver of performance of the barrier in most BSL-3 facilities. That is not to say that safety takes a backseat but it recognizes two key facts in a BSL-3 biosafety strategy: working with live agent and infected animals in primary containment devices means the room should not have airborne hazards present airflow. The room is secondary containment;1 and the main system that provides the secondary containment against airborne hazard escape is directional airflow.

The smallest amount of directional airflow has been shown to effectively prevent the escape of airborne agents independent of the air-tightness of the room.² Leaky rooms may actually be beneficial where there is significant negative pressure in the BSL-3 room—a gentle flow inwards prevents turbulence and unpredicted air currents that can flow counter to the movement of air from less to more hazardous zones.

Primary containment systems, biosafety cabinets, and sealed ventilated caging systems are highly engineered systems validated for their containment performance. When these systems are working and used properly they should prevent any hazard from being airborne in the room, even if the room loses its negative pressure or even goes positive.

Therefore, the real risk is a double failure where the room pressure relationships and the biosafety cabinets (or ventilated caging systems) fail to function at the same time. Although this risk is real, the likelihood of these events happening together does not mandate a barrier that goes to any length to achieve zero air leakage. In fact, that makes little sense given that BSL-3 rooms typically have a gap under doors or other places of controlled leakage so that air can move across the barriers from least to higher hazard under normal operating procedures. It’s a bit like sealing every micro-crack in the dike when there’s a window left at least partially open.

Effective Fumigation
If the de-emphasis on airtight barriers in the above analysis worries you, there’s still hope.