The second level biological safety cabinet is the same as the biological safety cabinet. The gas also flows from the outside into the secondary biological safety cabinet, which is usually called the inflow. Inflow prevents aerosols generated during microbiological operations from escaping from the front operating window of the cabinet to the laboratory. However, they differ from primary biosafety cabinets in that only HEPA-filtered (sterile) air is allowed to flow over the work surface. A built-in fan draws air through the front opening into the cabinet and into the front grille. Therefore, the air that has not been filtered by the filter will not directly enter the working area, thereby protecting the samples and instruments stored inside the safety cabinet from being contaminated by the outside air.
A unique feature of the secondary biological safety cabinet is that the filter is filtered by vertical layered (non-directional) HEPA filters and a downward flow of air is formed inside the cabinet. The constant flow of air can create internal air-borne infections inside the cabinet, thereby protecting the samples stored in the cabinet from infection. This kind of airflow is called subsidence.
The main difference between different types of secondary biological safety cabinets is that the proportion of exhaust gas and the proportion of gas recirculated through the air at high pressure are different. In addition, different secondary biological safety cabinets have different exhaust methods: Some safety cabinets filter air directly into the room, and some are discharged through the casing connected to the dedicated ventilation duct or through the exhaust system of the building. Outside the building.
In addition to the differences mentioned above, all secondary biological safety cabinets, like Tier 1 biological safety cabinets, can protect operators and laboratory environments from harm. In addition, the secondary safety cabinet also protects the product samples from contamination during microbial operations. The secondary biological safety cabinet can be used in the biological factor operation at one, two, or three levels of biological safety.