Biosafety cabinets are equipment that effectively reduces the chance of laboratory-acquired infection, reduces the chance of cross-contamination between people and samples or between samples, and is used to protect operators, laboratory environment, and biosafety of experimental materials.
In clinical laboratories, when operating infectious specimens or isolating and culturing pathogens or preparing strains, aerosols with a diameter of <5/zrn or droplets with a diameter of 5 to 100 μm that are invisible to the naked eye will be generated due to operations such as oscillation, shaking, pouring, stirring, pipetting, or spilling of liquids. These particles contain live pathogenic microorganisms that can be inhaled by operators or contaminate other samples on the work surface. Biosafety cabinets are equipment that effectively reduces the chance of laboratory-acquired infection, reduces the chance of cross-contamination between people and samples or between samples, and is used to protect operators, laboratory environment, and biosafety of experimental materials.
Types and characteristics of biosafety cabinets
In the past few years, the design of biosafety cabinets has been improved several times. The main improvements include two aspects: First, add a high-efficiency particulate air (HEPA) filter to the exhaust system. The HEPA filter can capture 99.97% of particles with a diameter of 0.3 ban; the capture of particles >0.3 swollen reaches 99.9%. This allows all known infectious factors to be effectively trapped, ensuring that the exhaust gas does not contain microorganisms; second, the HEPA-filtered gas covers the surface of the workbench, so that the operating equipment on the table is not contaminated. According to the different levels of biological containment, there are currently three types of biosafety cabinets designed: Class I, Class II, and Class III. When purchasing, you can determine the type of protection required according to the nature of your work and choose the corresponding biosafety cabinet.
Class I Biosafety Cabinet
Class I Biosafety Cabinet (Figure 1) allows the air in the laboratory to enter the biosafety cabinet from the front opening at a minimum rate of 0.38 m/s and be discharged from the safety cabinet through the exhaust duct. The directional flow of air can quickly take away the aerosol formed on the workbench without contacting the operator, and is directly discharged through the pipeline and then filtered by HEPA. There are 3 forms of discharge:
① discharged into the laboratory, and then discharged to the outside of the building through the laboratory exhaust system;
② discharged directly to the outside of the building through the building's exhaust system;
③ discharged directly to the outside of the building.
HEPA filters can be installed in the pressure exhaust system of the biological safety cabinet or in the exhaust system of the building. Some biological safety cabinets have integrated exhaust fans, while others use the exhaust fans of the building's exhaust system. Class I biological safety cabinets are simple in design and widely used. They can provide personal and environmental protection, and can also be used for operations involving contact with radionuclides or volatile chemicals. Since the incoming gas is unpurified laboratory air, it does not provide anti-contamination protection for the operating items.
Class II biological safety cabinets
Class II biological safety cabinets are also called laminar flow biological safety cabinets. The difference from the industrial-grade biological safety cabinet is that the incoming air is first filtered by HEPA to ensure that the air covering the countertop is sterile, which not only provides personal protection, but also protects the samples from contamination. Class II biosafety cabinets are divided into Class II A and Class II B, which can be further divided into Class II A 1, Class II A 2, Class II B 1, and Class II B2. Class II biosafety is self-contained. 70% of the flowing air can be recycled and reused repeatedly.
This type of biosafety cabinet is suitable for cell or tissue culture and operations involving pathogens of level 2 to 3 hazardous levels. If you wear positive pressure protective clothing, you can perform operations involving infectious factors of level 4 hazardous levels in a Class II biosafety cabinet.
Class II A Biosafety Cabinet
The Class II A Biosafety Cabinet has a built-in fan that draws laboratory air into the safety cabinet at a rate of 0.38 m/s, passes through the HEPA filter and then goes downward, splits at 6.18 cm from the workbench surface, and passes half through the front exhaust grille and the other half through the rear exhaust grille. All aerosols or droplets generated in the experiment are carried away by the downward airflow. The airflow reaches between the two HEPA filters on the top of the safety cabinet through the exhaust channel. At this time, about 70% of the gas returns to the operating area in the cabinet through the air supply HEPA filter for reuse, and the remaining 30% of the gas is exhausted to the laboratory after the exhaust filter for repeated use, or exhausted to the outside through the exhaust system of the building.
External exhaust level II
Type A2, B1, B2 biological safety cabinets are all derived from type II A1 biological safety cabinets. These biological safety cabinets have their own characteristics, including the speed of air intake from the opening, the amount of air recirculated on the work surface, the amount of air discharged in the cabinet, the exhaust system of the safety cabinet, and the pressure device. Different types of biological safety cabinets can be used for different experimental purposes.
The difference between type A and type B of type II biological safety cabinets is that the amount of circulating gas and exhaust gas covering the work surface is different, and the exhaust system is different. Detailed information can be obtained from the manufacturer's instructions.
Class III Biosafety Cabinet
The entire environment of the Class III biosafety cabinet is completely enclosed. The incoming gas is filtered by HEPA, and the exhausted gas is filtered by two layers of HEPA. There is a special system to keep the pressure in the cabinet at 124.5Pa, which is a negative pressure state, which can provide the best personal protection and is used for the operation of pathogens with a dangerous degree of 4. During the experiment, two operators can put their hands into the glove box for operation. There is a sterilizable transfer box equipped with a HEPA filter exhaust device next to the cabinet. There is a box soaked in chemical disinfectants under the cabinet. The safety cabinet can be connected to a double-door autoclave to receive sterilized items and move used materials out of the safety cabinet for sterilization. Several glove boxes can be connected together to increase the working area. Class III biosafety cabinets are suitable for laboratories with Class III or Class IV biosafety levels.
Ventilation connection of biosafety cabinet
Class II A1 and A2 external exhaust biosafety cabinets have "sleeve type" or "umbrella exhaust hood type" connections. The sleeve is installed on the exhaust duct of the safety cabinet to introduce the exhaust gas from the safety cabinet into the exhaust system of the building. An opening with a diameter difference of 2.5 cm is left between the sleeve and the exhaust duct of the safety cabinet to allow the air in the laboratory to be drawn into the exhaust system of the building. The exhaust capacity of the building must be able to meet the exhaust requirements of the room and the cabinet. The sleeve must be removable or designed to be able to perform operational tests on the biosafety cabinet. Generally, fluctuations in the building's air flow will not have a significant impact on the function of the biosafety cabinet with sleeve connection.
Class II B1 and B2 biosafety cabinets are firmly connected to the building's exhaust system through hard pipes, that is, without any openings, or preferably to a dedicated exhaust system. The exhaust volume and static pressure of the building's exhaust system must be exactly the same as the requirements specified by the manufacturer. It takes more time to certify a biosafety cabinet with hard duct connection than a biosafety cabinet that recirculates air back to the room or uses a sleeve connection.
Selection of biological safety cabinets
When purchasing a biological safety cabinet, you should consider whether the biological protection provided is for the operator or for the experimental samples; if it is for the operator, it should be clear whether it is for pathogenic microorganisms or toxic chemicals or both. If it is for pathogenic microorganisms, the biohazard level of the microorganism should also be emphasized; if it is for toxic chemicals, you can choose according to the following principles: No volatile or toxic chemical operations are performed in industrial or Class II A biological safety cabinets. Class II B1 biological safety cabinets can only be used for operations with a small amount of volatile or toxic chemicals. If a certain amount of volatile or toxic chemicals is to be operated, a Class II B2 biological safety cabinet must be used. Different types of biological safety cabinets have different exhaust characteristics.
Choosing the right biological safety cabinet is crucial to ensuring the safety of laboratory work. By considering the above factors, laboratory managers can ensure that the selected biological safety cabinet can meet the experimental needs and provide the necessary safety protection. Before purchasing, it is recommended to conduct sufficient market research and comparison to find the biological safety cabinet that best suits laboratory needs.
