Readers are beginning to respond to the question we posed in the October issue regarding why Class II biological safety cabinets have not lived up to expected levels of protection.
by Hank Rahe
We had referenced an article in the July issue of the American Journal of Health System Pharmacy that described surface contamination in hospital cancer centers using Class II biological safety cabinets. The article presented data indicating there were concentrations of cytotoxic agents above exposure guidelines [“Contaminants found outside Class II BSCs,” CleanRooms, October 1999, page 1].
The theories for the contamination that were offered in our last discussion [“A call to arms,” CleanRooms, October, 1999, page 12] are:
- Due to the pressure differential in the transfer of the antineoplastic liquids via syringe, vapors are formed. These vapors are too small to be captured by the HEPA filters.
- The transfer of materials into and out of the open face of the BSC combined with operator movement into and out of the BSC disturbs air flows, thereby OdraggingO contamination out of the BSC.
- Training is the problem. Poor technique is the cause resulting in area contamination.
- All of the above.
From the information received, the final theory was indicated to be the leading candidate as the reason for the excessive exposure potential reported earlier.
Studies on Class II biological safety cabinets, which were conducted by a major pharmaceutical company, have indicated that activities that create pressure on liquids, such as transfers using syringes or filling nozzles, can create sub-micron droplets or vapor that can pass through the HEPA filters.
The transference of materials and the movement of people into and out of the biological safety cabinets also pose a significant contamination problem. For example, such items as gloves and gown sleeves will naturally become contaminated by the activity inside the biosafety cabinet environment. When withdrawn, they contaminate the surrounding environment. The operator has the choice to either remove the contaminated items inside or outside of the environment. Because most choose to remove the gloves outside of the hood, the contamination is brought with them, thus increasing the potential for contaminating the surrounding environment.
While lack of attention to the proper positioning and movement of the arms during aseptic manipulations can be called poor technique, in most cases there are unrealistic expectations. Considering the level of concentration that is demanded for most operations, the required limitations of movement and proper positioning within the laminar flow environment create difficult working conditions.
It is interesting that most of the feedback from non-operational sources cited the lack of training as the problem. However, individuals who work inside the environment cited the continual movement of the person and of materials into and out of the laminar flow, since they are difficult to control with perfect technique.
Of those who contacted me, several have indicated there is data available to support the theory that the two major sources for contamination and exposure to cytotoxic compounds is the transfer of materials out of the front of the cabinets and vapor or sub-micron mist, which can pass through the HEPA filters.
Hank Rahe is director of technology at Contain-Tech in Indianapolis. He has over 30 years experience in the healthcare industry, as well as four years in academia. He is an expert in the areas of conventional and advanced aseptic processing. He is the past chairman of the board of the International Society of Pharmaceutical Engineers, and is a member of the CleanRooms Editorial Advisory Board.