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Analysis of Personnel Safety Risks of Class II Biosafety Cabinets

The first-level isolation barrier in biological laboratories (Class II biosafety cabinet) faces the following associated risks:

●Fan performance

The static pressure dynamic range is overly narrow while the output gas flow rate drops too quickly. This risk pattern is associated with the nominal inflow air velocity. The lower the nominal inflow air velocity, the earlier the risk occurs. The physical nature of the risk hazard is that the inflow air velocity vector is lower than the aerosol spraying bacteria rate. Especially when the operator's arm or experimental instrument is moved out of the front opening of the biosafety cabinet, aerosols are easily exposed to escape along the upper edge of the opening, and personnel are endangered as they may inhale it.

●Equivalent air flow cavity effect at the upper edge of the opening

The inflow air velocity is defined as the average velocity, but the actual velocity vector is highly non-uniform. As can be known from measuring the inflow air velocity with an anemometer, the ratio of the average values of the measurement points at the 25% and 75% height levels in the horizontal direction is at least three times. The velocity vector distribution of the air flow shows a state of high at the bottom and extremely low at the top. The average air flow velocity vector along the upper part of the opening is the lowest value, and the ability to resist the escape of microbial aerosols is the lowest. Relative to the microbial spraying bacteria rate of 0.5m/s±0.05m/s, it is almost an inflow air flow cavity. The risk probability of personnel contamination increases under dynamic conditions where the operator's arm moves during operation, when the hand and experimental instrument are moved out of the opening, or when the microbial sample size is large or the aerosol concentration is high. In the case of combined fan output gas flow reduction, the risk probability of personnel contamination increases rapidly. The mechanism of personnel contamination thus formed is inhalation or exposure of mucous membranes for inoculation, which may explain the reason for the unexplained infection of clinical laboratory personnel during the Covid-19 epidemic.

●Reduced isolation barrier ability due to cabinet integrity

The reduction of isolation barrier ability is related to cabinet integrity, especially prominent in the design of a single fan driving the downflow and exhaust airflows. The cabinet integrity of negative pressure biosafety cabinets in China is more sensitive to the reduction of inflow air velocity vector, because negative pressure accelerates the inward inflow gas flow, resulting in exhaust air volume being greater than inflow air volume. The outer cabinet with a butterfly valve and made of ordinary carbon steel with a surface coating reduces the front window isolation barrier ability of the Class II biosafety cabinet due to exposed holes or gaps at the junction of carbon steel plates and stainless steel inner walls.

Unique risk control technology

●Constant air volume control technology

The static pressure dynamic range of the GUARD A2 series biosafety cabinet system has been expanded. During the dynamic change process from the initial total static pressure to a twofold increase, the total gas flow reduction is converged to -3%. This empowers the stabilization of the inflow air velocity vector of the biosafety cabinet and improves the isolation barrier ability of biological laboratories. This new 3A technology also extends the one-time service life of high-efficiency air filters by four times, with significant technical and economic benefits. It has been patented. The constant air volume control technology not only breaks through the isolation barrier ability of existing safety cabinets but can even solve similar technical problems faced in fields such as laboratory systems, air showers, FFUs, isolators, and clean benches.

●Laminar flow downward air curtain technology

The laminar flow downward air curtain is the second isolation barrier of the Class II biosafety cabinet. It fills the inflow air flow cavity and works together with the inflow air flow to resist microbial leakage. The laminar flow downward air curtain is an original design of the Class II biosafety cabinet.

●Stainless steel seamless integrated cabinet technology

Seamless integration is the guarantee of cabinet integrity, aiming to achieve the effectiveness and durability of personnel safety. This design not only makes the outer cabinet seamless and integrated but also requires seamless integration between the inner wall of the operation chamber and the outer cabinet to highlight the design and technological capabilities of the GUARD A2 series biosafety cabinets.

Unique product protection design of the GUARD A2 system

●Reshape the organizational structure of the downward airflow

This design is aimed at eliminating the blind area of downward airflow in the space near the side wall of the operation chamber, thus establishing a new airflow structure model with full coverage of downward airflow in the operation area.

Design methods include: eliminating the blind area of downward airflow and eliminating the physical space for aerosol retention and diffusion; full coverage of downward airflow in the operation chamber; comprehensive application of "zero leakage physical control technology" between the high-efficiency air filter and the cabinet structure to achieve "biological sterility" in the operation chamber of the biosafety cabinet.

Bacterial particles are expressed as a threshold group from 0.5μm to 10μm. The air purification level of the operation chamber of the GUARD A2 system is not inferior to level 3@0.3μm. The sampling boundary is 30mm from the left, right, and rear sides.

New launch

product description:

The Guard A2 series biosafety cabinet uses cutting-edge intelligent technology to realize the function of automatically identifying the relationship between power and air volume and static pressure, has an automatic sensing mechanism of air flow and static pressure changes, and can automatically adjust the wind speed (3A). This design concept aims to realize the expansion of the static pressure range of the system, the conservation of the total gas flow of the system, and the conservation of the gas velocity vector, so as to effectively prevent the potential risks caused by the fluctuation of the total gas flow and the excessive monotone decline of the personnel and products, and ensure the safety of personnel and products during the microbial experiment operation.

● Continuous welding by argon arc welding to ensure the integrity and durability of the cabinet with welding penetration;

● Transverse wiredrawing of the external surface area of the cabinet and polishing of the surface of the trim board. Operating chamber bare surface drawing treatment, beautiful and durable;

● The radius of curvature is 14 mm at the intersection of the rear sidewall and the left and right sidewalls of the operating module, which is convenient to clean.

Exquisite workmanship:

The initial negative pressure of the system is about -52 Pa; The initial positive pressure value is about 96 pa, the test is to increase the initial negative pressure reading to 2 times of the initial positive pressure reading.The total static pressure is gradually increased by decreasing the intake grid area.

Differential pressure gauge:SWEMAAIR 3000（Sweden）

Anemometer:SWEMAAIR 3000（Sweden）

During the evolution from -52 Pa to -150 Pa, the downdraft velocity vector displayed by the wind velocimeter is kept at 0.33 m / s; In the process of -150Pa to -270Pa, the airflow velocity vector displayed by the wind velocimeter is 0.34m / s, and the difference of the airflow velocity vector in the process of -52Pa to -270Pa is 0.01 m / s.

Because of the conservation of the total gas flow rate, the technical term of less than 20% airflow fluctuation is abandoned. During the static operation of the system (8h), the inflow flow velocity or downflow velocity is stable throughout the operation process, and there is no air fluctuation.