Four reasons for not using open fire in biosafety cabinet

Class II biological safety cabinet (BSC) uses HEPA filtration and laminar air flow to provide protection for operators, environment and samples For aseptic purposes, HEPA filters are usually 99.99 +% efficient for particles of 0.3 micron size Typical microbiological procedures usually use Bunsen burners or other open fires to disinfect and / or reduce cross contamination; however, such open fires are not recommended in BSCs for several reasons: Class II BSCs maintain sample protection by uploading a stream of air (air moving in one direction at a constant speed, without turbulence) up to the lower level of the cabinet's work area The hot air rises, so any open fire will make the air rise to the laminar flow and fall, generate turbulence and hinder the BSC's ability to protect samples in the working area If the open fire becomes too hot, it also has the ability to melt the adhesive, which holds the HEPA filter medium on its frame This undermines the effectiveness of HEPA filters and results in a loss of containment in the positive pressure ventilation system If the flame goes out and the air supply valve remains open, the combustible gas will be introduced into the cabinet unrestricted In the A2 biosafety cabinet, 70% of the air in the BSC is recycled (see the video below), and the concentration of combustible gas may reach the explosive potential, which poses a serious risk not only to the BSC, but also 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 microbiological and biomedical laboratories, 5th Edition ，（BMBL 5th）。 When working in BSC, some measures can be taken to reduce the possibility of cross contamination of materials Open pipes or bottles should not be placed vertically Researchers using Petri dishes and tissue culture plates should keep the lid above the open sterile surface to reduce the direct impact of downward air to a large extent Do not place caps or caps on towels Items should be re covered or closed as soon as possible There is no need for an open fire in the near microbial free environment of the biosafety cabinet On an open bench, the neck of the combustion culture vessel will produce an upward airflow to prevent microorganisms from falling into the tube or flask However, the open flame in the BSC creates turbulence, which destroys the HEPA filtered air mode supplied to the work surface Touch pad micro burners equipped with indicator lights to provide flame on demand can be used when deemed necessary The air disturbance and heat accumulation of internal cabinet will reduce Zui The burner must be shut down after the work is completed Small electric "furnace" can be used to purify bacterial rings and needles, and is superior to open fire in BSC Disposable or recyclable sterile rings should be used whenever possible As mentioned in the CDC above, if flame is considered necessary, the widely used equipment type is a safer alternative to Bunsen burner Some of them use low-key pedals to dampen the flames; others detect movement.