There are several technologies typically used to transfer samples, materials and waste into and out of the Class III BSC. These include dunk tanks, pass through chambers, double door autoclaves and rapid transfer ports (RTP).
Dunk tanks allow for the passage of potentially contaminated materials out of the BSC without breaching containment. It also allows for live samples to be removed for transfer to another lab or for archive. The exterior of the primary container is surface decontaminated and packaged in a secondary container which is kept in contact with a chemical decontaminating solution in the dunk tank for a prescribed period of time. The decontaminant and contact time are specified in laboratory SOPs, as is how frequently the decontaminant should be changed, and how recently it should be prepared prior to conducting work in the BSC. The liquid must also be checked to ensure it is one inch, or the level specified by the manufacturer above the stainless steel divider that bisects the dunk tank. Having a liquid level above the divider is needed to maintain containment and separation of unfiltered air from the room and Class III BSC.
Dunk tanks can be designed with coved or oblong shapes for ease of cleaning, may be slightly graded for ease of draining, and can be designed with ‘cages and polls’ to keep containers and bags submerged, and retrieve the cages from the bottom of the tank for easy removal. Kynar or Halar coatings should be bonded to the interior surfaces of the stainless steel dunk tank to protect them from the corrosive effects of many decontaminants. A latch and administrative SOP or a timed interlock ensures both lids of the dunk tank are not opened at once, and that the material has been in appropriate contact with the decontaminant.
Oval slide-out dunk tank
Pass through chambers allow for clean materials to be passed into the Class III BSC. Potentially contaminated materials should not exit the BSC via the pass through chamber unless they are double contained with the package surfaces decontaminated. The interior of the chamber should be surface decontaminated when materials are passed from the Class III to another location as even though the containers are surface decontaminated, there could be trace contaminants on the gloves, which could then contaminate the pass through chamber. Once the inner door has been opened (between the chamber and the BSC) the chamber should be sprayed and surface decontaminated at the end of the experiment, or prior to opening the outer door that interfaces with the room (i.e. when additional supplies are to be introduced into the pass through chamber to the BSC).
Pass through chambers doors are gasketted and airtight, and the chamber may be non-ventilated, or ventilated with the exhaust air HEPA filtered prior to release. Typically the chambers have two doors, one that traverses the lab to the interior of the chamber and the other which connects the interior of the chamber to the interior of the BSC. There can be doors servicing other areas as well. All doors should be interlocked, with an audible and visual alarm indicating when a door is not fully closed after an appropriate period of time has elapsed to transfer materials.
Pass through chamber view on Class III BSC exterior
Double door autoclaves are very useful in passing large items into the Class III BSC and to sterilize bulky waste and material at the end of the experiment. The 5th Edition BMBL advocates a double door autoclave be integral with the Class III BSC for BSL-4 cabinet laboratories.
Double door autoclave integral to Class III BSC
Rapid Transfer Ports (RTP) provide the user a safe, efficient and time saving method to introduce and remove material from a Class III BSC without potentially contaminating the laboratory. RTP come in a variety of sizes ranging from small to very large cart mounted versions for animal transport in containment. They can be made in stainless steel or high durability plastic.
The RTP maintains containment as its design features a beta flange lid exterior that mates to an alpha flange door exterior that is attached to the Class III BSC. The lid and door are rotated and sealed and must form an interlock before door inside the BSC can be opened. This exposes only the interior of the RTP cylinder to air and materials inside the BSC. The process is reversed to uncouple the RTP. The contents can be stored or the RTP can be opened with an allen key inside a Class II BSC where the materials are removed and the interior of the RTP is surface decontaminated for reuse.
Exterior of the sealed RTP being mated to the exterior of the BSC