“If you know the enemy and know yourself you need not fear the results of a hundred battles”, said the Chinese warrior Sun Tzu.
As our enemies in a battle, viruses can differ a lot, each of them with their own weapons to cause diseases, and strategies to spread in the population. Knowing the characteristics of our enemies and our own weapons to defend ourselves and counterattack (the availability of vaccines and treatments) allows us to assign all viruses, and all microorganisms in general, to a biological risk group:
- Risk group 1: microorganisms that do not cause any disease
- Risk group 2: microorganisms that cause disease to humans or animals, represent a moderate risk for the community, vaccines are available
- Risk group 3: microorganisms that cause severe disease and can easily spread in the population, vaccines are available
- Risk group 4: microorganisms that cause severe disease and can easily spread in the population, vaccines are not available
To each risk group corresponds a biosafety level, which implies a specific set of rules describing the personal and collective protective equipment (to protect the operator and the environment, respectively), as well as the structural characteristics of the laboratories in which these microorganisms can be handled.
In the past, I have worked with the hepatitis viruses HBV and HDV, and now I work with SARS-CoV-2: they all belong to risk group 3, and must be handled in appropriate biosafety level 3 (BSL3) laboratories. Such laboratories are not directly accessible from the outside, and are delimited by at least an anteroom with a double door. The pressure inside de lab is lower than outside, so that the air can move exclusively into the lab, making it impossible for any volatile material, including viruses, to escape. As an additional safety measure, it is forbidden to work solo in a BSL3 lab.
To work with SARS-CoV-2 or any other group 3 microorganism, we need to wear two protective lab suits: the one in direct contact with our body is waterproof and washable, while the one in contact with the air is waterproof and disposable. The outer suit has a hood and a zipper that must be completely fastened to cover the neck. We also wear two pairs of gloves; the outer glove is longer and partially covers the forearm. The portion of the ankle between the shoes and the rim of the suit must be covered with waterproof material as well.
Mouth and nose are protected by a FFP3 mask, and on top of that we wear a hood with a face screen, connected to a Powerd Air-purifying respirator (PAPR), which we wear as a belt bag. The PAPR actively pumps the air through a filter to the inside of the hood causing a difference in pressure, so that only the filtered air can enter into the hood.
Within the lab, the virus can be handled exclusively inside a biosafety cabinet, a workstation provided with filters, and partially opened only on one side. On the open side, a vertical air flow provides two important functions: 1) forces the incoming air directly towards the filters before it can circulate in the workstation, and 2) prevents the air and the microorganisms to leave the interior of the hood. This guarantees that the biological material will not be contaminated and that the operator can work safely.
Only the hands and the forearms of the operator can go inside the biosafety cabinet, the other parts of the body are separated from the workstation by a glass screen. Every time the operator needs to move from the cabinet to another area of the lab, hands and forearms (covered by the gloves) must be cleaned with a virucidal product; the same must be done with any other object removed from the cabinet.
At the end of the experiment, the biological samples are properly stored, and the safety cabinet, the entire lab, as well as the protective clothing potentially exposed to the virus, must be disinfected. The layers of protective equipment worn by the operators must be removed following a specific order. The hood with the respirator are disinfected and stored in air-tight containers. Gloves, shoe covers, the mask and the disposable suit will be disposed of as potentially contaminated waste.
The exit from the BSL3 lab has a built-in automatic shower to guarantee that no biological residue is carried outside. Access to level 3 laboratories is restricted to authorized personnel, to ensure that the correct procedures are followed and that the studies are always carried out safely for both the operator and the society.
Bibliography
Virus&Co. 
Where do virus and viruses come from is Mystery is it not?
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