Share thisA look at the benefits and limitations of directional air inflow
In the first column1 in this series related to the benefits and limitations of directional airflow for biocontainment, we discussed the issues related to directional airflow within a room (or zone) of a facility and the issue of how much protection comes from directional airflow within a containment room. The conclusion that was reached was that personnel protection should not be expected from directional airflow within a zone and that facilities should be designed and operated with that in mind.
In the second column2 on directional airflow, we shared some thoughts on another aspect of directional airflow; the realities and expectations of directional airflow between zones. The issues surrounding directional airflow into the room at the boundary, where doors and other openings allow interface with the adjacent spaces, is very complex. We began to look at the three major containment conditions related to directional airflow at the doorway 1) facilities with leaky (gaps for directional airflow) doors with exhaust systems filtered, 2) facilities with fully sealed (airtight) doors and exhaust systems filtered, and 3) facilities with leaky doors with exhaust systems unfiltered.
As stated in the second column, the ability to reduce containment risk with directional airflow varies between containment facilities with airtight doors and leaky doors. “Consider that a biosafety cabinet has a fragile air barrier with an inflow velocity of 100 linear feet per minute (approximately 1 mile per hour) that is easily disrupted by fast movement or airflow disruptions. Remember that a biosafety cabinet is a carefully engineered, finely balanced, standardized piece of laboratory equipment. Consider then that the inward airflow velocity at the open door of a containment laboratory might average significantly less. For example, a door that is seven feet high and three feet wide with 200 cubic feet of air moving through it would have an inflow velocity of less than 10 linear feet per minute, about 1/10th of a mile an hour.”
In the third column,3 we reviewed issues that were encountered in higher level containment laboratories with sealed doors (except when used for ingress or egress). When these doors are closed, there is no directional airflow across the sealed containment barrier. They require very different thinking in the design of the containment barrier and HVAC systems.
In this article, we will return to the condition of the leaky door and the directional airflow issues typically encountered at this condition. What are the benefits and limitations of directional air inflow? What should the expectations be?