According to the 1992 version of the NSF49 standard in the United States, the medium of biosafety level 1 (P1) refers to ordinary harmless bacteria, viruses and other microorganisms; the medium of biosafety level 2 (P2) refers to general pathogenic bacteria, viruses and other microorganisms The medium of biosafety level 3 (P3) refers to microorganisms such as potent/lethal bacteria and viruses, but can be cured after infection; the medium of biosafety level 4 (P4) refers to microorganisms such as potent/lethal bacteria and viruses, There is no cure.

Class I biological safety cabinet refers to a fume safety cabinet used to protect the safety of operators and the environment, but not to protect the safety of samples. It is suitable for the operation of media with no requirements on the safety of processing samples and with biohazard levels of 1, 2, and 3. Because it does not consider whether the processed samples will be polluted by the air entering the cabinet, the requirements for the cleanliness of the air entering the cabinet are not high; the air flow is unidirectional and non-circulating, and the air enters the cabinet after passing through the HEPA filter. After passing through the workbench, it is filtered and discharged through the exhaust port; in order to protect the safety of the operator and the environment, the inward non-circulating suction airflow must be kept away from the operator; the gas in the safety cabinet must pass through HEPA before it is discharged to the atmosphere. filter filter.

Class II biological safety cabinet refers to a ventilated safety cabinet used to protect operators, process samples and the environment. The cabinet maintains a negative pressure state and is suitable for the operation of media with biological hazard levels 1, 2, and 3.

Class II biological safety cabinets are the most commonly used type of biological safety cabinets in clinical biological protection. When dealing with high-concentration or large-capacity infectious materials in clinical practice, Class II biological safety cabinets are the most used. According to the US NSF49 standard, Class II biological safety cabinets are generally divided into four types: A1, A2, B1, and B2.

Type A1: (1) maintain the minimum average suction inlet wind speed (calculated or measured value) passing through the opening surface of the workbench as 0.38m/s (75ft/min); (2) send out from the static pressure box, pass through the HEPA filter The filtered vertical airflow is a part of the mixed vertical airflow and suction airflow (that is, 70% of the gas in the cabinet is recirculated to the work area through the HEPA filter, and 30% of the gas is filtered out through the HEPA filter at the exhaust port); (3) allows The airflow filtered by the outlet HEPA filter returns to the laboratory; (4) Positive pressure pollution air duct and static pressure box are allowed.

Type A2: (1) Maintain the minimum average suction inlet wind speed passing through the opening surface of the workbench at 0.5m/s; (2) The vertical airflow filtered by the HEPA filter is mixed with the vertical airflow discharged from the static pressure box and the suction airflow The last part (that is, 30% of the gas in the cabinet is removed through the HEPA filter at the exhaust port, and 70% of the gas is recirculated to the work area through the HEPA filter at the gas supply port); (3) All exhaust gas must be filtered by the HEPA filter. Only then can it be exhausted to the outside, but the exhaust gas can no longer enter the safety cabinet for circulation or return to the laboratory; (4) All air ducts and static pressure boxes contaminated by biological contamination should maintain negative pressure or be surrounded by negative pressure air ducts and static pressure boxes.

Type B1: (1) maintain the minimum average suction inlet wind speed (calculated or measured value) passing through the opening surface of the workbench as 0.5m/s (100ft/min); (2) in the vertical airflow filtered by the HEPA filter The vast majority is composed of uncontaminated circulating inhaled airflow (that is, 70% of the gas in the cabinet is removed through the HEPA filter at the exhaust port, and 30% of the gas is recirculated to the work area through the HEPA filter at the gas supply port); (3) after Most of the polluted vertical airflow filtered by the HEPA filter is filtered through a dedicated air duct and then discharged into the atmosphere; (4) All air ducts and plenum boxes contaminated by bio-contamination should maintain negative pressure, or the air ducts and Surrounded by a plenum.

Type B2 (also known as “full row” type): (1) maintain the minimum average suction inlet wind speed (calculated or measured) through the open surface of the workbench at 0.5m/s (100ft/min); (2) The vertical airflow filtered by the HEPA filter is fed by laboratory or outdoor air (that is, the gas discharged from the safety cabinet does not enter the circulation process of the vertical airflow); (3) all the suction airflow and vertical airflow pass through the HEPA filter After being filtered, it is discharged into the atmosphere, and will not enter the safety cabinet for circulation or return to the laboratory; (4) All polluted air ducts and static pressure boxes should maintain negative pressure, or be surrounded by air ducts and static pressure boxes that are directly exhausted.

Class III biological safety cabinets are fully airtight, airtight ventilated safety cabinets, suitable for the operation of media with biological hazard levels 1, 2, 3 and 4. The working space is unidirectional flow air purified by HEPA filter without swirl. The incoming air is filtered by several HEPA filters and sent to the safety cabinet, and the exhaust air should be filtered by double-layer HEPA filters or filtered by HEPA filters and incinerated for treatment.