Biological Safety Cabinet
The biological safety cabinet is designed to protect operators, laboratory environment and experimental materials from possible infectious aerosols and spatters during the process of handling infectious experimental materials such as primary cultures, strains and diagnostic specimens. To meet different biological research and epidemic prevention requirements, the biological safety cabinet can be divided into three categories: Level I, Level II and Level III. It's widely used in such fields as medical care, disease prevention and control, food hygiene, bio-pharmacy, environmental monitoring, and various biology laboratories. It lays an important foundation for ensuring bio-safety and environmental safety, being a means to improving people's livelihood.
Main Classification
To meet different biological research and epidemic prevention requirements, the biological safety cabinet can be classified into three categories: Level I, Level II and Level III.
The Level I biological safety cabinet can protect staff and the environment rather than samples. Its principle of air flow is the same as that of the fume hoods in labs, except that the air outlet of the biological cabinet is equipped with a HEPA filter. And all types of biological safety cabinets are set with a HEPA filter at the air outlet and the air inlet. The Level I biological safety cabinet has no fan itself and relies on the fan in the external vent pipe to drive airflow. It has been seldom used at present due to its failure to provide protection for test samples or products.
The Level II biological safety cabinet is now the most widely used type. Like the Level I biological safety cabinet, it also has airflow into the front opening, namely "inflow air", so as to prevent aerosols that may be generated during microbial operations from escaping from the opening. Yet unfiltered inflow air will be captured by its air grille before reaching working area, so that the test samples won't be polluted by the outside air. A unique feature of it is that the vertical laminar flow filtered by the HEPA filter blows down from the top of the cabinet, namely "downward flow". The downward flow continuously blows through the working area of the cabinet to protect the test samples inside from external dust or bacterial contamination.
According to the regulations of NSF49, the Level II biological safety cabinet can be divided into 4 types according to the inlet air velocity, exhaust mode and circulation mode: Type A1, Type A2 (formerly called Type B3), Type B1 and Type B2. All types of Level II cabinets can provide protection for workers, environment and products.
The minimum or measured average air velocity at the front opening of the Type A1 cabinet shall be at least 0.38m/s, while that of the Type A2 cabinet shall be at least 0.5m/s. In those two types of cabinets, 70% of the air is recirculated to the working area through the HEPA filter, and 30% is filtered out from the air outlet. And the design of negative pressure surrounded polluted area in Type A2 cabinet prevents the leakage of material inside.
All type B cabinets are safety cabinets connected to the exhaust air system. The fan connected to the exhaust duct of the cabinet is connected to the emergency power supply, which is to maintain negative pressure even during a blackout to prevent the leakage of dangerous gas (such as gas in labs). The minimum or measured average air velocity at the front opening should be at least 0.5m/s (100fpm). As for the Type B1 cabinet, 70% of the gas is filtered out by the HEPA filter at the air outlet, and 30% is recirculated to the working area through the HEPA filter at the air inlet. The Type B2 cabinet is a kind of safety cabinet with air 100% filtered out and with no internal circulating airflow, which can provide both biological and chemical safety control simultaneously.
The Level III biological safety cabinet is designed for BSL-4 laboratories, and is the safety cabinet with highest class of safety protection in the world. It is completely airtight and air is 100% filtered out with no gas involving in the circulation. Staff operates the cabinet by wearing the gloves connected to the cabinet (commonly known as the glove box). The pass box with two doors, suitable for high-risk biological tests, is adopted to send test samples into the cabinet and protect them from pollution.
According to the regulations of mandatory industry standard of safety cabinets, YY0569-2005 Biological Safety Cabinet (People's Republic of China Pharmaceuticals Industry Standard), only products that have obtained three-category medical device registration certificate issued by the State Food and Drug Administration (SFDA) can truly protect operators, laboratory environment and operated samples.
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