4 reasons not to use open flame in biosafety cabinets

Class II Biosafety Cabinets (BSC) use HEPA filtration, laminar airflow to provide operator, environmental and sample protection. For sterility purposes, the efficiency of a HEPA filter is typically 99.99 +% for particles of 0.3 micron size.

Typical microbial procedures typically use Bunsen burners or other open flames to disinfect and/or reduce cross-contamination; however, this type of open flame is not recommended for use in BSC for several reasons:

Class II BSCs maintain sample protection by delivering a downward laminar airflow (air unidirectionally traveling at a constant rate without turbulence) over the working area of the cabinet. Hot air rises, so any open flame will cause the air to rise to a laminar flow, creating turbulence and obstructing the BSC's ability to protect samples in the work area.
 

If the open flame becomes too hot, it also has the ability to melt the adhesive, which holds the HEPA filter media on its frame. This destroys the effectiveness of the HEPA filter, resulting in loss of containment in a positive pressure ventilation system.
 

If the flame is extinguished and the air supply valve remains open, the combustible gas will be introduced into the cabinet without restriction. In the A2 biosafety cabinet, 70% of the air in the BSC is recycled (see video below), and the concentration of flammable gas may reach explosive potential, which is not only for the BSC, but also poses a serious risk to users and laboratories.

 

The Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH) also address this in their publications: Biosafety in Microbiology and Biomedical Laboratories, 5th Edition. , (BMBL 5th).

When working in the BSC, some measures can be taken to reduce the possibility of cross-contamination of materials. Open tubes or bottles should not be placed vertically. Researchers using petri dishes and tissue culture plates should keep the lid over an open sterile surface to minimize direct impact of the downward air. The cap or cap should not be placed on the towel. Items should be re-covered or covered as soon as possible. No open flame is required in a near microbial environment in a biosafety cabinet. On an open bench, burning the neck of the culture vessel will create an upward flow of air to prevent microbes from falling into the tube or flask. However, open flames in the BSC create turbulence that disrupts the pattern of HEPA filtered air supplied to the work surface. When it is deemed absolutely necessary, a touchpad micro-burner equipped with an indicator light to provide a flame on demand can be used. Internal cabinet air disturbances and heat buildup will be minimized. The burner must be turned off after the work is completed. A small electric "furnace" can be used to purify bacterial rings and needles and is superior to open flames in BSCs. Disposable or recyclable sterile rings should be used whenever possible.

 

As described in the CDC above, the widely used type of equipment is a safer alternative to Bunsen burners if it is considered absolutely necessary. Some of them use a low-key pedal to attenuate the flame; others detect motion.