TB Infection Control

I cannot agree that a BSC Class II Type A does not need a thimble or tight connection when we are speaking about BL3 laboratory (TB laboratory dealing with concentrated culture, doing DST). A thimble connection to the exhaust system is needed to assure biosafety when HEPA-filters are leaking. It happens even in a very well maintained by engineers laboratory. If we are speaking of many TB laboratories in the world working in the surrounding of poor infrastructure, this precaution is absolutely necessary. Thimble connection is more simple than tight connection as the later needs good balance with exhousting system. When planning engineering systems actual risks shiould be estimated. I am sorry to intrude in P. Jensen field and hope he will provide better consultation.

Best regards,
M. Shulgina

Best regards,
M. Shulgina

A tight connection on the exhaust of a Type A BSC is strictly forbidden as it makes the cabinet unsafe and it no longer is approved according to ANSI/NSF 49. The thimble connection should have it own exhaust fan as most building exhaust systems do not hacve sufficient static pressure to operate a thimble adequately. In addition NSF 49 calls for an alarm at the cabinet to signal when the roof exhaust fan is not in operation when the cabinet is turned on.

Melvin First

Discussion contents: Guidelines and specifications for managing TB laboratory equipment and supplies say: Laboratories should discourage use of Class IIA1 BSCs because they may have contaminated ducts and plenums at a positive pressure to the room.

Reply Contents.Some countries are using Class IIA without any thimble connection system to exhaust and air comes from BSC recirculates in the room.Most of the time even they don't follow regular certification and maintenance of BSC. Obviously,it is more hazardous than protective and very dangerous for Lab staffs as well as surrounding environment..We need a consensus whether the lab will be allowed to perform Mtb culture in absence of thimble connection to exhaust system or not while they are using BSC IIA.


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Sarder Tanzir Hossain
B.Sc.(Hon's) and M.S. in Microbiology (DU)
Microbiologist
Health Program, BRAC Afghanistan.
Website:http://www.brac.net,www.bracafg.org

I agree with Dr. First 100% and in addition you can not have a positive pressure exhaust ductwork in the building. since Class II A1 should not be connected to the exhaust system there will be no positive pressure exhaust ductwork and the Class IIB2 which have a direct connection should have an interlock betweent the BSC fan and the building fan so incase Building Fan is not operation the BSC fan will shut down and go into alarm mode. Goind back to the original discussion, it is much simpler to operate and maintian a Class II A BSC and if they are certified annually they should be very safe to work at.