Biosafety levels
Biosafety levels are process of keeping the harmful biological agents under control. It includes the precautions required to isolate dangerous microbes in as laboratory. There are four biosafety levels are designed from lowest biosafety to highest biosafety i.e. BSL 1 to BSL 4. The precautions level consist of regular and washing and minimal protective equipment at lowest level as the Biosafety level increases precautions taken also increases which may includes airflow systems, multiple containment rooms, sealed containers, positive pressure personnel suits, established protocols for all procedures, extensive personnel training, and high levels of security to control access to the facility.
The biosafety levels are determined by considering the following criteria :
• Risks related to containment
• Origin of the microbe
• Severity of infection
• Transmissibility
• Route of exposure
• Nature of the work conducted

Levels:
Biosafety level 1
Biosafety level 1 (BSL-1) is level of precaution in which well-characterized agents which do not cause disease in healthy humans is used. These agents should cause minimal potential hazards to laboratory personnel and the environment. At the level 1 of biosafety, precautions used are very less as compare to other higher biosafety levels. The person working in the Laboratory must wash their hands upon entering and exiting the lab. Research work done at biosafety level 1 does not involved use of special containment equipment and it can be performed on standard open laboratory benches. However, eating and drinking should be prohibited in laboratory areas. The special care should be taken while disposal of Potentially infectious material. Before disposal of the infectious material used it must be decontaminated either by adding an appropriate disinfectant, or by packaging for decontamination elsewhere. Personal protective equipment (PPE) is only required for circumstances where personnel might be exposed to hazardous material. BSL-1 laboratories must have a door which can be locked to limit access to the lab; however it is not necessary for BSL-1 labs to be isolated from the general building.
Biosafety level 1 is suitable for work with various kinds of microorganisms which includes non-pathogenic Saccharomyces cerevisiae, Escherichia coli, Bacillus subtilis, and other organisms not suspected to contribute to human disease. Due to the low level of safety required and less hazardous to human health BSL-1 laboratory are the types of laboratories generally used as teaching spaces for high schools and colleges.
Biosafety level 2
At this level, the precautions taken for the safety are higher than level 1. All precautions used at Biosafety Level 1 are followed, and some additional precautions are taken. BSL-2 differs from BSL-1 in that:
• The person working in Laboratory must have specific training in handling pathogenic agents and are directed by scientists with advanced training.
• While working is conducted in the laboratory access in the laboratory must be limited
• Extreme precautions are taken with contaminated sharp items.
• Biological safety cabinets or other physical containment equipment are used in the certain procedures in which infectious aerosols or splashes may be created.
Biosafety level 2 is suitable for work which involved agents of moderate potential hazard to the personnel as well as environment. This includes various microorganisms that cause mild disease to human. Examples include Hepatitis A, B, and C viruses, Staphylococcus aureus, Salmonella, Plasmodium falciparum, human immunodeficiency virus (HIV), pathogenic Escherichia coli, and Toxoplasma gondii.

Biosafety level 3
Biosafety level 3 is appropriate for work which involved handling of microbes which can cause serious and potentially lethal disease witn the mode of the inhalation. Researcher working with influenza virus under biosafety level 3 conditions used respirator inside a biosafety cabinet (BSC).
This type of work can be done in teaching, clinical, diagnostic, research or production facilities. Here, the precautions considered in biosafety level 1 and 2 must be followed, as well as additional measures also includes:
• All laboratory persons working in laboratory are provided medical surveillance and must be offered relevant immunizations (where available) to reduce the risk of an accidental or unnoticed infection.
• All procedures of research which involved the use of infectious material must be done within a biological safety cabinet.
• Laboratory personnel must provide with solid-front protective clothing (i.e. gowns that tie in the back). The protective clothing used for working cannot be worn outside of the laboratory and must be discarded or decontaminated after each use.
• A laboratory-specific biosafety manual must be drafted which details how the laboratory will operate in compliance with all safety requirements.
• The entrance to the laboratory must be separated from areas of the building with unrestricted traffic flow.
• Additionally, the laboratory must be behind two sets of self-closing doors (to reduce the risk of aerosols escaping).
• The laboratory must be constructed in such a way that it can be easily cleaned. Carpets are not permitted, and any seams in the floors, walls, and ceilings are sealed to allow for easy cleaning and decontamination.
• The windows found in the laboratory must be sealed and a ventilation system installed in such a way that it forces air to flow from the “clean” areas of the lab to the areas where infectious agents are handled. Air from the laboratory must be filtered before it can be recirculated.
Biosafety level 3 is commonly used for research work and diagnostic laboratories involving various microbes which can be transmitted by aerosols and can cause the several diseases. These include Mycobacterium tuberculosis, Chlamydia psittaci Francisella tularensis, Venezuelan equine encephalitis virus, Eastern equine encephalitis virus, SARS coronavirus, Coxiella burnetii, Rift Valley fever virus, Rickettsia rickettsii, several species of Brucella, chikungunya, yellow fever virus, and West Nile virus.
Biosafety level 4
Biosafety level 4 (BSL-4) is the highest level of biosafety precautions and is appropriate for work with agents that could easily be aerosol-transmitted within the laboratory
• This level of biosafety work with microorganisms that can cause severe to fatal disease in humans for which there are no available vaccines or treatments.
• BSL-4 laboratories are generally set up to be either cabinet laboratories or protective-suit laboratories. In cabinet laboratories, all work must be done within a class III biosafety cabinet.
• The Materials needs to be discarding from the cabinet must be decontaminated by passing through an autoclave or a tank of disinfectant.
• The cabinets themselves are required to have seamless edges to allow for easy cleaning.
• The cabinet and all materials within the cabinet used must be free of sharp edges so that it cannot cause damage to the gloves.
• In a protective-suit laboratory, all work must be done in a class II biosafety cabinet by personnel wearing a positive pressure suit.
• To exit from the BSL-4 laboratory, the researchers or the persons must pass through a chemical shower for decontamination followed by a room for removing the positive-pressure suit, and then by a personal shower.
• Entry into the BSL-4 laboratory is restricted to trained and authorized individuals, and all persons entering and exiting the laboratory must be recorded. The entery for the other must be prohibited.As with BSL-3 laboratories; BSL-4 laboratories must be separated from areas that receive unrestricted traffic.
• Additionally airflow is tightly controlled to ensure that air always flows from “clean” areas of the lab to areas where work with infectious agents is being performed. The entrance to the BSL-4 lab must also employ airlocks to minimize the possibility that aerosols from the lab could be removed from the lab.
• All laboratory waste, including filtered air, water, and trash must also be decontaminated before it can leave the facility.
Biosafety level 4 laboratories are used for diagnostic work, clinical work and research on easily transmitted pathogens which can cause harmful disease. These include a number of viruses known to cause viral hemorrhagic fever such as Ebola virus, Lassa virus, Marburg virus, Crimean-Congo hemorrhagic fever. Other pathogens handled at BSL-4 include Nipah virus, Hendra virus, and some Flaviviruses. Additionally, poorly characterized pathogens which appear closely related to dangerous pathogens are often handled at this level until sufficient data are obtained either to confirm continued work at this level, or to work with them at a lower level. This level is also used for work with Variola virus, the causative agent of smallpox, though this work can only be done at the World Health Organization approved facilities at the Centers for Disease Control and Prevention in Atlanta, United States, as well as the State Research Center of Virology and Biotechnology in Koltsovo, Russia.