Biosafety Cabinet FAQ

The major difference between ULPA and HEPA is the filtered particle size and its corresponding efficiency. Typical HEPA is directed against the particles with a diameter of 0.3μm, and the elimination ratio is 99.97%. ULPA is directed against the particles with a diameter of 0.12μm, and the elimination ratio is 99.999%. Due to the different filtered particle size, so this is meaningless for comparing these two filters. From the viewpoint of pressure loss and the airflow volume, the filter structure of ULPA is much dense, so the range for filterable particle size is wider. On the contrary, large pressure loss and small volume of airflow will cause insufficient air change rate. A motor with higher horsepower will need to reach the same airflow volume as HEPA.

The major reason is that the particles (0.3μm) are generally difficult to be removed. Therefore, DOP (Di-octyl phthalate) or PAO (Poly alpha olefin) used to examine the elimination ratio of HEPA filter is heated to produce oil mist for examining the efficiency of filter.

The curve between the elimination ratio of the filter and particle size is just as follow. From the curve of elimination ratio, we can see the elimination ratio is the minimum while the particle size is 0.3μm. In general, the elimination ratio for HEPA filter to remove 0.3μm particles is over than 99.97%, and for particle over than 0.3μm (bacterial spore) or less than 0.3μm (virus), the elimination ratio can be enhanced to 99.999%. We have to clarify the wrong conception that the elimination ratio is reduced with the particle size reduce. For HEPA filter, this characteristic can efficiently intercept all known infectious media and assure the air exhausted from the biological safety cabinet is free of microbes.

Explain every operator about the use and limitation of the biological safety cabinet, and ask them to strictly follow the requirements, such as pre-preparation, reasonable placement of objects in the cabinet, regular maintenance and examination. The protection for operator can not be guaranteed while faulty operation, leaking, or damage happens. The air curtain in front of the biological safety cabinet is very fragile to be contaminated by interference, so the position of sash can not be casually changed, the movement should be moderate, and frequent in and out of the biological safety cabinet should be avoided for preventing the airflow from interference. During the operation, air turbulence can be formed by door open and close, personnel movement, or even cough behind the operator to increase the opportunity for leaking of microbial aerosols and contamination of the laboratory.

Previously, hard duct connection is widely used in Class II type A2 biological safety cabinet. Because the cabinet is connected to the exhaust blower, the airflow balance in the cabinet will be destroyed while the exhaust speed is unstable (increase or reduce). Consequently, operators, environment, and test samples can be contaminated severely. Class II type A2 biological safety cabinet is forbidden to connect with sealed hard duct by NSF 49 standard, but suggested to connect with exhaust canopy. The exhaust canopy is installed on top of the exhaust HEPA filter in biological safety cabinet, and left 2.5 cm of interstice for inhaling the air in the room to this exhaust system. This is the safest connection. The airflow in the cabinet is independent, so the airflow balance in the cabinet will not be affected by fluctuation of this exhaust system.

     For many laboratories, they think connection of exhaust duct to outdoor is safer than indoor after purchasing a type A2 biological safety cabinet. In fact, there is a HEPA filter at the exhaust outlet of biological safety cabinet, so the air will be filtered by HEPA filter before exhausting to outdoor. The safety of exhausted air is guaranteed, and it will not contaminate the indoor environment. You can be relieved for this concern, because international related organizations (such as NSF) will address discussions and reminders for the users, if there is a problem. In addition, if indoor treated air is exhausted to outdoor, it is very energy-consuming for the whole operation in a laboratory. The cost can be increased largely, so you should take a prudent consideration.a

The most simple way is to check whether this biological safety cabinet is approved by National Standard or not, such as NSF 49 or EN12469. If this biological safety cabinet is approved by National Standard which means its design, structure, and performance has reached the international safety level, so you can use by feeling relieved. There is a bonus effect for special function or design flaunted by other manufacturers, but those are unnecessary devices.
At the same time for looking approved products, the users have to pay attention on: when manufacturers claim their biological safety cabinet conforms to certain international standard, you can ask them show the examination report signed by one legal examination foundation. In addition, some standards might not have direct relationship with the safety of biological safety cabinet. For example, the manufacturer claims they are approved by ISO 9001 quality examination, but ISO 9001 is not applicable to international examination standard of biological safety cabinet. So, you should pay attention on this point.

In general, Class II biological safety cabinet is sufficient for normal demands, Class III biological safety cabinet is needed unless you have to process some unknown species, virus, and live tissues. For experiments processed with non-toxic, non-radioactive, or non-volatile chemical specimens, type A2 biological safety cabinet can mostly satisfy the requirements. Whether type B2 100% exhausted biological safety cabinet is needed or not, deliberate evaluation should be taken. The users have to specially pay attention on that the biological safety cabinet will be shut due to exhaust by duct connection, because insufficient exhaust amount (without compliance with manufacturer’s requirement).
In addition, from the viewpoint of energy-saving, type A2 biological safety cabinet can save more energy due to the circulation airflow which mostly exhaust into the indoor. On the contrary, type B2 biological safety cabinet is 100% exhausted to the outdoor which means the air in the laboratory will be exhausted, so its cost on air-conditioner is much higher than type A2.

Laminar flow hoods only provide the protection for test specimen, but the operator and environment. Biological safety cabinet can provide the protection for operator, environment, and test specimen simultaneously. So, from the objects needs to be protected, you can understand what kind of machine is applicable to you.

※ Special remind: horizontal or vertical laminar flow hoods are not biological safety cabinet, so can not be used in operation with biological hazard.