How to choose a biological safety cabinet?

1: Concepts related to biosafety cabinets The concept of biosafety has a narrow sense and a broad sense.
The narrow sense biosafety refers to the prevention of the negative effects caused by the development and application of modern biotechnology, that is, the possible impact on biodiversity, ecological environment and human health.
danger or potential risk
.

Biosafety in the broad sense is not only aimed at the development and application of modern biotechnology, it covers the concept of biosafety in the narrow sense and includes a wider range of content
.

It is roughly divided into three aspects: the first refers to human health and safety; the second refers to agricultural biosafety on which human survival depends; and the third refers to environmental biosafety related to human survival
.

Therefore, biosafety in a broad sense involves multiple disciplines and fields: preventive medicine, environmental protection, plant protection, wildlife protection, ecology, pesticides, forestry, etc.
, and the management work belongs to different administrative departments
.

Many domestic understandings of biosafety are still limited to a narrow concept
.

2.
Relevant regulations and standards: Order of the State Council of the People's Republic of China "Regulations on Biosafety Management of Pathogenic Microbial Laboratories" People's Republic of China Health Industry Standard WS233-2002 "General Guidelines for Biosafety of Microbial and Biomedical Laboratories" National Standard of the People's Republic of China GB19489- 2004 "General Requirements for Laboratory Biosafety" National Standard of the People's Republic of China GB19781-2005 "Medical Laboratory Safety Requirements" III: Biosafety level classification According to the degree of harm of the biological factors being operated and the protective measures taken, the protection of biological safety The biosafety level (BSL) is divided into four levels, with level I protection level and level IV being the highest protection level; they are represented by BSL-1, BSL-2, BSL-3, and BSL-4 respectively
.

NIH (National Institutes of Health) classified as P1\P2\P3\P4 CDC classified as BSL1\BSL2\BSL3\BSL4 infectious bacteria (virus) classification (Classification of Pathogens) a class: Yersinia pestis, cholera Vibrio, smallpox virus, HIV, SARS virus two types: hepatitis virus, rabies virus, leprosy, brucella, hemorrhagic fever virus, dengue virus, typhus rickettsia three types: meningococcus, Streptococcus, Neisseria gonorrhoeae, Mycobacterium tuberculosis, Haemophilus pertussis, Corynebacterium diphtheriae, Salmonella, Clostridium tetanus; Leptospira, Treponema pallidum; Japanese encephalitis virus, polio virus, influenza virus, rubella virus , measles virus, mumps virus four: the difference between biological safety cabinets and ultra-clean workbenches Ultra-clean benches are horizontal laminar flow ultra-clean benches, they discharge HEPA high-efficiency filtered air through the working surface and blow it directly to the operator
.

These devices provide product protection only
.

They can be used for certain clean jobs, such as sterile equipment or dust-free assembly of electronic equipment
.

These clean benches cannot be used when working with cell culture material or drug synthesis or when working with potentially infectious materials
.

Operators may be exposed to these materials (including protein antigens) while using the clean bench, which can cause allergies
.

Horizontal laminar flow clean benches should never be used in place of biological safety cabinets in biomedical or veterinary laboratories
.

Vertical laminar flow "clean benches"  They may be useful in hospital pharmacies, since these devices generally have a viewing window from which air is usually vented into the room
.

Biosafety cabinet is: a negative pressure filter fume hood, used for biosafety protection in biosafety laboratories and other laboratories, which can prevent operators and the environment from being exposed to biological aerosols generated during the experiment; Provide safety protection for samples and cross-contamination between samples and the environment
.

According to the national pharmaceutical industry standard YY0569-2005, biological safety cabinets are divided into three grades: I, II, and III according to the design structure of airflow and isolation barrier
.

Types of biological safety cabinets Average inflow airflow velocity (m/s) Air flow pattern protection object Class I 0.
7-1.
0 100% evacuated personnel, environment Class II, Type A1 ≥ 0.
4 70% circulation, 30% evacuated personnel , environment, sample Class II, Type A2 ≥ 0.
5 70% cycle, 30% expulsion personnel, environment, sample Class II, Type B1 ≥ 0.
5 30% cycle, 70% expulsion personnel, environment, sample Class II, Type B2 ≥ 0.
5 100% expelled personnel, environment, samples Class III N/A 100% expelled personnel, environment, samples Class I Biological Safety Cabinet Use: In many cases, Class I biological safety cabinets are used as special containment equipment (e.
g.
, centrifugation, harvesting equipment or small fermentation equipment) or processes that may generate aerosols (such as dumping cages, aerated cultures, or tissue agitation)
.

Class II Biological Safety Cabinet Features: Class II (Type A1, A2, B2, and B2) biological safety cabinets provide personnel, environmental, and product protection
.

Personal protection: Air is drawn from around the operator to the grille in front of the safety cabinet to provide personnel protection
.

 Product Protection: HEPA high-efficiency filtered air flows down the working surface of the safety cabinet in a unidirectional flow, minimizing the chance of cross-contamination and providing product protection
.

Environmental protection: Because the air in the safety cabinet passes through the exhaust HEPA high-efficiency filter, there is no pollution to the environment (environmental protection), and the exhaust air can be circulated back to the laboratory (Type A) or discharged outside the building through pipes (Type B) Class III biosafety cabinets  Class III biosafety cabinets are designed for handling microbial pathogens at biosafety level 4, providing maximum protection for the environment and operators
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It is an airtight structure without an open viewing window
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Items are transferred into the cabinet through a soaking tank or double door transfer box (like a pressure cooker) that can be sterilized between uses
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Conversely, items can also be safely removed from the Class III biological safety cabinet
.

The supply air and exhaust air are filtered by HEPA high-efficiency filter
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Exhaust air must pass through two stages of HEPA filters, or a HEPA filter and an air incinerator, before being discharged to the outdoor atmosphere
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Use a dedicated independent exhaust system to maintain the airflow inside and outside the cabinet, which can keep the safety cabinet under negative pressure (usually about 0.
5 inches of water column pressure)
.

five.
The "main part" of the biological safety cabinet 1.
High-efficiency filter; under the rated air volume, the air filter with a particle size greater than or equal to 0.
3μm capture efficiency of more than 99.
97% and airflow resistance below 245Pa
.

Generally, there are two types of HEPA filters (high efficiency particulate air filter) that can filter out particles greater than or equal to 0.
3 μm, and ULPA filters (ultra-high efficiency particulate air filter) that can filter out particles greater than or equal to 0.
12 Article 4.
2.
4 of the Biosafety Cabinet Industry Standard of the People's Republic of China clearly stipulates that the material of the high-efficiency filter cannot be made of paper
.

Substances that may be released from the filter media must not adversely affect personnel, the environment and equipment
.

At the same time, it is also stipulated that the leakage rate of the scannable detection filter should not exceed 0.
01% at any point; the leakage rate of the non-scannable detection filter should not exceed 0.
005% at any point
.

2.
Article 5.
4.
13 of the industry standard for biological safety cabinets of the People's Republic of China guarantees that when the safety cabinet is in normal operation without adjusting the speed control of the fan, and the wind pressure through the filter drops by 50%, the exhaust volume of the fan should not drop by more than 10%.
%
.

The biological safety cabinet must be able to automatically control the wind speed of the fan within a certain range and automatically adjust according to the change of the load to ensure that the output air volume is in the best state and the relative stability of the negative pressure in the biological safety cabinet, so as to ensure the stability of the airflow in the working area of ​​the safety cabinet.
Prevent the air curtain from being unsafe
.

Single fan design and dual fan design Due to the aging of the two fans is not synchronous, which leads to the change of the ratio of the circulating air volume inside the machine, which makes the safety cabinet unsafe
.

If the external exhaust fan of the other two fans fails, the polluted airflow cannot be discharged from the safety cabinet, which will cause the polluted airflow to flow backward, which is very unsafe
.

The safety cabinet designed with a single fan does not have the above safety hazards at all
.

3.
Control system The People's Republic of China biological safety cabinet industry standard 5.
3.
10.
5 Class II biological safety cabinet must display the downdraft and inflow velocity of the work area in real time.
When the downdraft and inflow velocity fluctuate more than their nominal value of 20 %, use the sound and light alarm to prompt
.

The airflow velocity ensures the blocking effect of the airflow on the diffusion or escape of dangerous particles such as aerosols generated during the test.
drop
.

Dfliter control panel barcode display HEPA filter life technology
.

4.
Optimized cabinet structure design Article 5.
3.
1 of the People's Republic of China Biological Safety Cabinet Industry Standard The working area of ​​Class II A2, B1, and B2 safety cabinets should adopt a four-sided (left and right, rear, bottom) double-layer structure
.

All contaminated parts of the three types of safety cabinets should be under negative pressure or surrounded by negative pressure channels and negative pressure ventilation systems
.

The three-sided side wall panels in the exposed working area of ​​Class II and III safety cabinets should be integrally formed, and the splicing of the inner surface must be sealed
.

It can be seen that China's YY0569 standard more clearly regulates the cabinet structure design of the safety cabinet compared with the European and American standards, and is more in line with the current experimental requirements in biology and chemistry
.

5.
Detection method There are two ways to test the anti-leakage performance of the safety cabinet in Article 6.
3.
1 of the biological safety cabinet industry standard of the People's Republic of China, the pressure decay method and the soap bubble method
.

The pressure decay method to test the anti-leakage performance of the biological safety cabinet is the most accurate and demanding test method.
It has very high requirements on the airtightness of the biological safety cabinet and the overall design of the cabinet.
The test method recommended by biological safety cabinet standards such as NSF49 in the United States
.

People's Republic of China biological safety cabinet industry standard 6.
3.
6.
3.
3 Potassium iodide method (KI-Discus) personnel protection test KI-Discus test is a test that can verify the pollution control performance of safety cabinets on the spot.
The injection speed is much higher than that of the Bacillus subtilis spores from the microbial sprayer, which means that it has a stronger ability to break through the safety air curtain of the safety cabinet, and it is safer to use this method to detect qualified safety cabinets; second, potassium iodide and palladium chloride The discoloration reaction can be completed within 1 minute, far less than the 48-hour culture of the microorganism method, and the detection is rapid
.

This makes it a reality for safety cabinet manufacturers to test each safety cabinet that leaves the factory, ensuring the safety of the product
.

Article 6.
3.
7 of the biological safety cabinet industry standard of the People's Republic of China uses a thermal anemometer to measure the downdraft flow rate in the safety cabinet
.

The downdraft flow rate plays an important role in the protection of the safety cabinet test sample and cross-infection protection.
For example, if the airflow rate is too small, the test sample will lose protection
.

Both YY0569 and EN12469 stipulate the permissible range of downdraft flow rate for secondary safety cabinets to be 0.
25-0.
5m/s, while NSF49 does not give any downdraft rate requirements
.