The appropriate BSL for a project is determined jointly by the project leader, institutional biosafety experts and biosafety committees. The BSL assigned to a project is based on a biological risk assessment that takes into account: Laboratory biosafety describes the application of specific practices, safety equipment and laboratories specifically designed to create a safe environment inside and outside the laboratory to work with infectious agents and toxins. In addition, there is surveillance of professionally acquired infections and, if necessary, staff training. 1Although U.S. guidelines allow air circulation, this is not recommended. All airflow from biosafety cabinets must be 100% extracted and the exhaust air must be HEPA filtered before leaving the building. All declawing areas and outlet valves must be designed for 100% exhaust air, including all feed and infiltration air flows. 2The entire airflow must be HEPA filtered, whether it sucks in or recirculates. In some versions, duplicate in-line HEPA filters have also been implemented as standard. 3The term „negative pressure“ does not mean that the clean room is under atmospheric pressure.

Rather, it means that it is negative compared to surrounding areas, which must have the same or higher cleanliness classification when airflow is taken from other areas. Therefore, „dirty“ or gray spaces above the ceiling must be airtight. The pressure difference shall be at least 0.05 in W.G. from non-biosecure areas, but a design of 0.06″ W.G. (not necessarily documentation) is recommended to provide a security control tolerance (see note 4 below). 4It is strongly recommended to separate the equipment that serves these specific areas from the rest of the facility. For example, although these rooms are separated, a secondary barrier should be provided for devices located in „dirty“ or gray areas to separate them from the rest of the installation. This zone must be negative in relation to the atmosphere, possibly above the „pressurized“ closed zone.

The decontamination, cleaning and maintenance of this equipment is separated and provides an additional safety barrier for the rest of the plant. 5Additional checks/latches are also recommended/required. The design team must ensure that these areas are maintained under negative indoor air pressure (relative to adjacent areas) at all times, and must evaluate any HVAC systems that serve these areas, in addition to systems that serve the areas around the containment zones. 6Determined areas that enter (do not exit) these biosecurity levels (e.g., B changing rooms) can be designed for positive airflow to areas outside biosafety, while airflow to the biosafety zone is pressurized. BSL 3 facilities need to place greater emphasis on primary and secondary barriers to protect the community and the environment, as well as laboratory staff. Ventilation systems therefore play a major role in these installations. This is because it works with indigenous or exotic agents with a potential for respiratory transmission, which can cause a serious and potentially fatal infection. Tuberculosis and St. Louis encephalitis virus are representative of the microorganisms associated with this containment level.

Laboratory handling is performed in a biosafety cabinet or other enclosed equipment that acts as a primary barrier. Secondary barriers include controlled access to the room and ventilation systems that minimize the release of infectious aerosols from the laboratory. BSL 4 laboratories work with dangerous and exotic agents that pose a high individual risk of life-threatening diseases that can be transmitted by aerosol and for which there is no vaccine or treatment. Viruses such as Congolese-Crimean haemorrhagic fever are handled at this level of biosecurity. The main danger to personnel working with BSL 4 pathogens is respiratory exposure to infectious aerosols, mucous membranes or exposure to broken skin to infectious droplets and self-onoculation. Working with these active substances poses a high risk of exposure and infection to laboratory personnel, the community and the environment. Each biological laboratory, regardless of the level of biosafety, follows normal microbiological practices. Each level of biosecurity is based on the controls of the next lower level.

Each level of biosecurity has its own specific containment controls. The assignment of a biosafety level to a specific work process is carried out by means of a protocol-based risk assessment. BSL-3 laboratories are used to study infectious agents or toxins that can be transmitted through the air and cause life-threatening infections. The researchers carry out all the experiments in a biosecurity cabinet. BSL-3 laboratories are designed to be easily decontaminated. As an additional safety measure, these laboratories must use controlled or „directed“ airflow to ensure that air flows from non-laboratory areas (e.B.dem corridor) to laboratory areas. .