Pass through chambers provide an easy way of moving supplies and materials in-to and out-of the Class III Biological Safety Cabinet. There are a few options to consider with these devices. To begin with, their interior surfaces should be coved for ease of cleaning, and the exterior of the chamber should not extend into an area where there is foot traffic. The doors must provide an airtight seal to allow of gaseous/vapor decontamination and prevent the leakage of air from the Class III BSC into the laboratory.
Doors should also be electronically interlocked to prevent a breach of containment. If they are not electronically interlocked there should be either an alarm light or audible warning to let the user know when one door is open. If they are interlocked, consideration should be given to an override switch that is positioned in a location that would require a deliberate motion for activation. At some point pieces of equipment or tools that exceed the size of the pass through may need to be introduced or removed, hence the desire for an interlock override. This is important if the Biological Safety Cabinet does not have an integral autoclave, or the item can not be passed out through the autoclave.
Class III Biosafety Cabinets Pass Through Chamber: Choosing the Right Size
How do you decide what size pass through is needed? The user(s) should take measurements of the equipment/supplies that have the greatest dimensions in terms of height, length and depth that will be used on a regular basis. How long are the pipettes? How tall is the animal isolator(s)? What are the dimensions or the microfuge? The interior measurement of the chamber when both doors are closed, should accommodate the equipment with a little room to spare.
Class III BSC Pass Through Chamber: Ergonomics
Size, shape and location of the pass through is also impacted by ergonomics. Recall, the user must reach into the BSC through a gloveport and enter the pass through at a slight angle. Items being removed must be within the users grasp, or the user will need a tool (tongs, preferably with a rubberized gripping surface) to reach further back to retrieve supplies. Thought has to be given to what materials are in the front of the chamber near the users hand (media, samples, squeeze bottle with decontaminating solution, etc), and what can reasonably by accessed with tongs (absorbent toweling). It is actually not so easy to get a good grip with tongs and remove pipette tips from the back of a pass through chamber. Optimally, the user should be able to wipe down the surfaces with toweling after the chamber has been sprayed with a decontaminant.
There is no rule that says a user can only have two doors on the pass through. Many Class III Biosafety Cabinets constructed for use by military and security forces have an additional door built into the chassis of the mobile laboratory that leads from the outside in-to the Class III BSC. This prevents the sample collector or person delivering the sample from having to enter the laboratory. The number of doors and what they access is driven by the mission and user requirements.
HEPA Filtered Ventilated Pass Through Chambers
Based on requirements the user may also opt for having a HEPA filtered ventilated pass through chamber. Ventilated chambers are commonly seen when a laboratory may receive a mixed sample that could contain a volatile chemical compound, but are also used when the pass through is the primary method of removing samples and other items from the Class III BSC that may not otherwise be removed via the dunk tank (animals in cages, plated samples, experiments that need to remain upright, etc). Some users prefer the added safety of knowing the air in the chamber has been purged, and the pass through chambers exhaust system creates inward airflow upon opening the door to the lab. Airflow varies with the airflow rate in the chamber of the BSC and the cubic volume of the interior of the pass through chamber. Even if the chamber is ventilated, material leaving the Biological Safety Cabinet should be surface decontaminated and placed in a secondary container which is sprayed with decontaminant before being placed inside the pass through. If a non-ventilated chamber is used, the same procedure as above can be followed with the addition of spraying the interior of the pass through chamber to facilitate the settling of any aerosols in the chamber. Whether ventilated or not, at the end of work, or upon a spill in the chamber, the pass through chamber must be decontaminated.