The "big act" of biological safety cabinet in laboratory construction
The biosafety cabinet protects the operator, the laboratory environment, and the laboratory materials from exposure to the above operations in order to manipulate infectious materials such as primary cultures, bacterial strains, and diagnostic specimens. Designed for the production of infectious aerosols and spills. The biosafety cabinet level applied in the laboratory biosafety level provides protection.
Biosafety cabinets can be divided into three categories: primary, secondary and tertiary to meet different biological research and epidemic prevention requirements.
The primary biosafety cabinet protects the staff and the environment without protecting the sample. The airflow principle is the same as for a laboratory fume hood, except that the vent is fitted with a HEPA filter. All types of biosafety cabinets use HEPA filters in the exhaust and air intakes. The first-class biosafety cabinet itself has no fan, and relies on the fan in the external air duct to drive the airflow. Since it cannot provide protection for the test articles or products, it has been used less frequently.
The secondary biosafety cabinet is currently the most widely used cabinet type. Like Class I biosafety cabinets, Class II biosafety cabinets also have airflow into the front window opening, known as the "inlet airflow", to prevent aerosols that may be generated during microbial operations from escaping from the front window. Unlike Class I biosafety cabinets, the unfiltered intake air stream is captured by the incoming grid before reaching the work area, so the test product is not contaminated by outside air. A unique feature of the Class II biosafety cabinet is that the vertical laminar airflow filtered through the HEPA filter is blown from the top of the safety cabinet and is referred to as the "downward flow." The sinking airflow is continuously blown through the working area of ​​the safety cabinet to protect the test items in the cabinet from external dust or bacteria.
According to the provisions of NSF49, the secondary biosafety cabinet can be divided into four levels according to the inlet airflow speed, exhaust mode and circulation mode: A1 type, A2 type (formerly B3 type), B1 type and B2 type. All secondary biosafety cabinets provide protection for workers, the environment and products.
The minimum airflow velocity or average value of the front window of the A1 safety cabinet should be at least 0.38m/s. 70% of the gas is recirculated through the HEPA filter to the work area and 30% of the gas is filtered through the vent. The minimum airflow velocity or average of the front window of the A2 safety cabinet should be at least 0.5m/s. 70% of the gas is recirculated through the HEPA filter to the work area and 30% of the gas is filtered through the vent. The negative pressure of the A2 safety cabinet surrounds the contaminated area and prevents the leakage of substances in the cabinet.
The Class B B biosafety cabinets are safety cabinets connected to the exhaust system. The fan connected to the exhaust duct of the safety cabinet is connected to the emergency supply power source, and the purpose is to maintain the negative pressure of the safety cabinet under the power failure to prevent dangerous gas leakage such as laboratory. The minimum airflow velocity or average of the front window should be at least 0.5m/s (100fpm). The B1 type 70% gas is removed through the vent HEPA filter and 30% of the gas is recirculated through the supply port HEPA filter to the work area. The B2 is a 100% full-row safety cabinet with no internal circulation airflow and provides both biochemical and chemical safety controls.
Performance ratio of each cabinet type of secondary biological safety cabinet
The Class III Biosafety Cabinet is designed for Class 4 laboratory biosafety levels and is the world's highest safety level safety cabinet. The cabinet is completely airtight, 100% fully exhausted, all gases are not involved in the cycle, the staff operates through the gloves attached to the cabinet, commonly known as the glove box (Golve box), and the test products enter and exit the safety cabinet through the double-door transfer box. Ensure that it is free of contamination and is suitable for high-risk biological tests.
An Exhaust Collar A2 type secondary biosafety cabinet can be used under operating conditions that allow the circulation of chemical gases. The discharge pipe cover is different from the general hard pipe in that it has an intake hole for sucking air; the discharge pipe cover is connected to the outer pipe and then connected to an external fan. The air intake on the drain pipe cover is essential for the A2 type II biosafety cabinet to maintain the balance of intake and sink airflow through the built-in fan. If a sealed external duct is used, the intake air flow will be too strong, which may cause the safety cabinet to protect the product; and the air inlet hole in the discharge duct cover can draw air from the room without affecting the airflow balance in the safety cabinet. This condition applies only to trace amounts of toxic chemicals.
If circulating chemical gases are not permitted, a B2 type secondary biosafety cabinet equipped with a rigid tube must be used. Since the B-type safety cabinet is not an independent balancing system, its built-in fan can only produce a downdraft flow, and the safety cabinet relies on an external exhaust fan to make the intake air flow. This type of safety cabinet is complicated to install and maintain, because the external exhaust fan must be balanced with the built-in fan, otherwise it will lead to the failure of the safety performance of the operator or product.
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