4 reasons not to use fire in a biological safety cabinet

Class II biological safety cabinet (BSC) uses HEPA filtration and laminar airflow to provide protection for operators, the environment and samples. For the purpose of sterility, the efficiency of the HEPA filter is usually 99.99+% for particles with a size of 0.3 microns.

Typical microbiological procedures usually use Bunsen burners or other open flames to disinfect and/or reduce cross-contamination; however, the use of such open flames in BSC is not recommended for the following reasons:

Class II BSC maintains sample protection by delivering downward laminar airflow (air traveling in one direction at a constant speed, without turbulence) over the working area of the cabinet. The hot air rises, so any open flame will cause the air to rise to a laminar flow drop, creating turbulence and hindering 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 undermines the effectiveness of the HEPA filter, resulting in the loss of containment in the positive pressure ventilation system.
 

If the flame goes out and the gas supply valve remains open, combustible gas will be introduced into the cabinet without restriction. In the A2 biological safety cabinet, 70% of the air in the BSC is recirculated (see the video below), and the concentration of combustible gas may reach explosive potential, posing a serious risk not only to the BSC, but also to users and laboratories. It occupies.

 

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

When working in BSC, some measures can be taken to reduce the possibility of material cross-contamination. The opened tube or bottle should not be placed vertically. Researchers using petri dishes and tissue culture plates should keep the lid above an open sterile surface to minimize direct impact of downward air. Do not put bottle caps or tube caps on the towel. Items should be re-covered or covered as soon as possible. There is no need for an open flame in the almost microorganism-free environment of the biological safety cabinet. On an open workbench, the neck of the burning culture vessel will generate upward airflow to prevent microorganisms from falling into the tube or flask. However, the open flame in the BSC creates turbulence, disrupting the HEPA filtered air supply to the work surface. When deemed absolutely necessary, a touchpad micro burner equipped with indicator lights to provide flames on demand can be used. Air disturbance and heat accumulation in the internal cabinet will be minimized. The burner must be turned off after the work is completed. The small electric "furnace" can be used to purify bacteria rings and needles and is better than the open flame in BSC. Whenever possible, use disposable or recyclable sterile loops.

 

As stated in the CDC above, if flames are considered absolutely necessary, the widely used equipment type is a safer alternative to Bunsen burners. Some of them use low-profile pedals to attenuate the flames.