Biological safety cabinet is currently the most widely used is the second level

Shanghai Haozhuang Instrument Co., Ltd. has developed the Hao Zhuang (LNB) brand biological safety cabinet, which is energy-saving and environmentally friendly, leading the country. Biological safety cabinets can be divided into three categories: first-level, second-level and third-level to meet different biological research and epidemic prevention requirements.
The first-level biological safety cabinet can protect the staff and the environment without protecting the samples. The airflow principle is the same as the laboratory fume hood, except that the exhaust port is equipped with a HEPA filter. All types of biological safety cabinets use filters in the exhaust and intake ports. The first-level biological safety cabinet itself does not have a fan, and relies on the fan in the external ventilation pipe to drive the airflow. Because it cannot provide protection for the test product or product, it has been rarely used at present.
The secondary biological safety cabinet is currently the most widely used cabinet type. Like Class I biosafety cabinets, Class II biosafety cabinets also have airflows into the front window openings, called "air intake streams", to prevent aerosols that may be generated during microbial operation from escaping from the front window. Unlike Class I biological safety cabinets, the unfiltered intake air flow will be captured by the inlet grille before reaching the work area, so the test article will not be polluted by outside air. A unique feature of the Class II biological safety cabinet is that the vertical laminar airflow filtered by the HEPA filter is blown down from the top of the safety cabinet, which is called "sinking airflow". The sinking air flow continuously blows through the work area of ​​the safety cabinet to protect the test products in the cabinet from contamination by external dust or bacteria.
According to regulations, secondary biological safety cabinets can be divided into four levels according to the inlet air velocity, exhaust mode and circulation mode: A1 type, A2 type, B1 type and B2 type. All secondary biological safety cabinets can provide protection for staff, environment and products.
The minimum amount or the average value of the air velocity of the front window of the A1 type safety cabinet of the test bench and fume hood should be at least 0.38m / s. 70% of the gas is recirculated to the work area through the HEPA filter, and 30% of the gas is filtered out through the exhaust port. The minimum amount or average value of the airflow velocity of the front window of A2 type safety cabinet shall be at least 0.5m / s. 70% of the gas is recirculated to the work area through the HEPA filter, and 30% of the gas is filtered out through the exhaust port. The design of the negative pressure of the A2 safety cabinet surrounding the contaminated area prevents the leakage of substances in the cabinet.
Type B biological safety cabinets are all safety cabinets connected to the exhaust system. The fan connected to the exhaust duct of the safety cabinet is connected to the emergency power supply, and the purpose is to maintain the negative pressure of the safety cabinet even when the power is off, so as to avoid the leakage of dangerous gases such as a laboratory. The minimum amount or average value of the airflow velocity of the front window should be at least 0.5m / s (100fpm). Type B1 70% of the gas is discharged through the exhaust port HEPA filter, and 30% of the gas is recirculated to the work area through the air supply port HEPA filter. Type B2 is a 100% full-row safety cabinet with no internal circulating airflow, which can provide biological and chemical safety control at the same time.
The performance of each type of the second-level biosafety cabinet is better than that of the third-level biosafety cabinet. The third-level biosafety cabinet is designed for the level 4 laboratory biosafety level and is currently the world's highest level of safety protection. The cabinet is completely airtight, 100% fully discharged, and all gases do not participate in the circulation. The workers operate through the gloves connected to the cabinet, commonly known as the glove box, and the test article enters and exits the safety cabinet through the double-door transmission box to ensure that it is not contaminated , Suitable for high-risk biological tests.
Under the operating conditions that allow the circulation of chemical gases, an A2 type secondary biological safety cabinet with an external discharge pipe cover can be used. The discharge pipe cover is different from the general hard pipe in that it has an air intake hole for sucking air; the discharge pipe cover is connected to the external discharge pipe and then connected to an external discharge fan. The air intake hole on the discharge duct cover is very important for the A2 type two-level biological safety cabinet to maintain the balance of the intake air flow and the sinking air flow through the built-in fan. If a sealed external air duct is used, the intake air flow will be too strong, which may result in the effectiveness of the safety cabinet's protection of the product; and the air intake hole on the exhaust duct cover can draw air from the room without affecting the airflow balance in the security cabinet. This condition applies only to trace amounts of toxic chemicals.

If chemical gases are not allowed to be circulated, a B2 type secondary biological safety cabinet equipped with hard tubes must be used. Because the B-type safety cabinet is not an independent balancing system, its built-in fan can only produce downdraft airflow, and the safety cabinet relies on the external exhaust fan to produce intake air flow. The installation and maintenance of this type of safety cabinet will be more complicated, because the external exhaust fan must be balanced with the internal fan, otherwise it will lead to the failure of the safety performance of the operator or product.

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