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Biohazard:
(A contraction of the words biological and hazard): Infectious agent(s), or part thereof, presenting a real or potential risk to the wall being of man, animals, and /or plants, directly through infection or indirectly through disruption of the environment.

Biosafety levels:
The combination of laboratory practices and techniques, safety equipment, and laboratory facilities appropriate for the operations performed and the hazard posed by the infectious agents and the laboratory function or activity. These biosafety levels are described in Biosafety in Microbiological and Biomedical Laboratories.

Biosafety Level 1:
Practices, safety equipment, and facility design and construction are appropriate for undergraduate and secondary educational training and teaching laboratories and for other laboratories in which work is done with defined and characterized strains of viable microorganisms not known to hepatitis virus, and exempt organisms under the NIH Guidelines for Research Involving Recombinant DNA Molecules are representative of those micro-organisms meeting these criteria. Many agents not ordinarily associated with diseases processes in humans are, however, opportunistic pathogens and may cause infection in the young, the aged, and immune deficient or immune suppressed individuals. Vaccine strains that have undergone multiple in vivo passages should be considered avirulent simply because they are vaccine strains.

Biosafety Level 1 represents a basic level of containment that relies on standard microbiological practices with no special primary or secondary barriers recommended, other than a sink for hand washing.

Biosafety Level 2:
Practices, equipment, and facilities are applicable to clinical, diagnostic, teaching, and other facilities in which work is done with the broad spectrum of indigenous moderate-risk agents present in the community and associated with human disease of varying severity.

With good microbiological techniques, these agents can be used safety in activities conducted on the open bench, provided the potential for producing aerosols is low. Hepatitis B virus, Human Immunodeficiency Virus, the Salmonellae and Toxoplasma spp. are representative of microorganisms assigned to this containment level.

Bio-safety Level 2 is appropriate when work is done with any human-derived blood, body fluids, tissues, or primary human cell lines where the presence of an infectious agent may be unknown. (Laboratory personnel working with human-derived materials should refer to the OSHA Bloodborne Pathogen Standard for specific required precautions.) Primary hazards to personnel working with these agents may include accidental percutaneous or mucous membrane exposures or ingestion of infectious materials. Extreme caution should be taken with contaminated needles or sharp instruments.

Even though organisms routinely manipulated at Biosafety Level 2 are not known to be transmissible by the aerosol route, procedures with aerosol or high splash potential, which may increase the risk of such personnel exposure, must be conducted in primary containment equipment or in devices such as biosafety cabinets (BSC) or safety centrifuge cups. Other primary barriers should be used as appropriate, such as splash shields, face protection, gowns, and gloves.

Secondary barriers such as hand washing sinks and waste decontamination facilities must be available to reduce potential environment contamination.

Biosafety Level 3:
Practices, safety equipment, and facility design and construction are applicable to clinical, diagnostic, teaching, research, or production facilities in which work is done with indigenous or exotic agents with a potential for respiratory transmission and which may cause serious and potentially lethal infection. Mycobacterium tuberculosis, St. Louis encephalitis virus, and Coxiella burnetii are representative of the microorganisms assigned to this level. Primary hazards to personnel working with these agents relate to autoinoculation, ingestion, and exposure to infectious aerosols.

At Biosafety Level 3, more emphasis is placed on primary and secondary barrier to protect personnel in contiguous areas, the community, and the environment from exposure to potentially infectious aerosols. For example, all laboratory manipulations should be performed in a BSC or other enclosed equipment, such as a gas- tight aerosol generation chamber. Secondary barriers for this level include controlled access to the laboratory and ventilation requirements that minimize the release of infectious aerosols from the laboratory.

Bio-safety Level 4:
Practices, safety equipment, and facility design and construction are applicable for work with dangerous and exotic agents that have a high individual risk of life-threatening disease, which may be transmitted via the aerosol route and for which there is no available vaccine or therapy. Agents with a close or identical antigenic relationship to Biosafety Level 4 agents also should be handled at this level. When sufficient data are obtained, work with these agents may continue at this level or at a lower level. Viruses such as Marburg or Congo- Crimean hemorrhagic fever are manipulated at Bio-safety Level 4.

The primary hazards to personnel working with Biosafety Level 4 agents are respiratory exposure to infectious aerosols, mucous membrane or broken skin exposure to infectious droplets, and autoinoculation. All manipulations of potentially infectious diagnostic materials, isolates, and naturally or experimentally infected animals pose a high risk of exposure and infection to laboratory personnel, the community, and the environment.

The laboratory worker’s complete isolation from aerosolized infectious materials is accomplished primarily by working in a Class III BSV or in a full-body, air-supplied, positive-pressure personnel suit. The Biosafety Level 4 facility itself is generally a separate building or completely isolated zone with complex, specialized ventilation requirements and waste management systems to prevent release of viable agents to the environment.

Bio-safety Cabinet Classification:
Although this Standard covers only Class II Biosafety cabinetry, Class I and Class III cabinets are currently defined and known to be commercially available. Biosafety cabinets can be used for work with biological agents assigned to biosafety levels 1 through 4, depending on the facility design as described in Biosafety in Microbiological and Biomedical Laboratories. Special note should be taken that BSL 4 agents should only be used in Maximum Containment Laboratories and that Class I and Class II biosafety cabinets are only acceptable in Maximum Containment Laboratories with positive pressure containment suits.

Class I Bio-safety Cabinet:
A ventilated cabinet for personnel and environmental protection, having an un-recirculated inward airflow away from the operator that exhausts all air to the atmosphere after filtration through a HEPA filter. Class I cabinets are suitable for work where no product protection is required.

Note: Although the traditional Class I BSC is exhausted to the atmosphere without recirculation into the lab, it is recognized that some of the benefits of the Class I BSC can be obtained even when the unit’s HEPA filtered exhaust is vented back into the laboratory.

Class II Bio-safety Cabinet:
A ventilated cabinet for personnel, product, and environmental protection having an open front with inward airflow for personnel protection, downward HEPA filtered laminar airflow for product protection, and HEPA filtered exhausted air for environmental protection.

Note: When toxic chemicals or radionuclides are used as adjuncts to biological studies or pharmaceutical work, Class II cabinets designed and constructed for this purpose should be used.

Class II Type A1 Cabinets (formerly designated Type A):
  • Maintain minimum average inflow velocity of 75 ft/min (0.38 m/s) through the work access opening.
  • Have HEPA filtered downflow air that is a portion of the mixed downflow and inflow air from a common plenum (i.e., a plenum from which a portion of the air is exhausted from the cabinet and the remainder supplied to the work area);
  • May exhaust HEPA filtered air back into the laboratory or to the environment through an exhaust canopy; and
  • May have positive pressure contaminated ducts and plenums that are not surrounded by negative pressure plenums.
Type A1 cabinets are not suitable for work with volatile toxic chemicals and volatile radionuclides.

Class II, Type A2 Cabinets (formerly designated Type B3):
  • Maintain  a minimum average inflow velocity of 100 ft/min (0.5 m/s) through the work access opening;
  • Have HEPA filtered downflow air that is a portion of the mixed downflow and inflow air from a common plenum
  • May exhaust HEPA filtered air back into the laboratory or to the environment through an exhaust canopy; and
  • Have all biologically contaminated ducts and plenums under negative pressure or surrounded by negative pressure ducts and plenums.
Type A2 cabinets used for work with minute quantities of volatile toxic chemicals and tracer amounts of radionuclides required as an adjunct to microbiological studies must be exhausted through properly functioning exhaust canopies.

Class II Type B1 Cabinets:
  • Maintain  a minimum average inflow velocity of 100 ft/min (0.5 m/s) through the work access opening;
  • Have HEPA filtered downflow air composed largely of uncontaminated re-circulated inflow air;
  •  Exhaust most of the contaminated downflow air through a dedicated duct exhausted to the atmosphere after passing through a HEPA filter; and
  • Have all biologically contaminated ducts and plenums under negative pressure or surrounded by negative pressure ducts and plenums.
Type B1 cabinets may be used for work treated with minute quantities of volatile toxic chemicals and tracer amounts of radionuclides required as an adjunct to microbiological studies if work is done in the direct exhausted portion of the cabinet, or if the chemicals or radionuclides will not interfere with the work when recirculated in the downflow air.

Class II Type B2 Cabinets (sometimes referred to as “total exhaust”):
  • Maintain  a minimum average inflow velocity of 100 ft/min (0.5 m/s) through the work access opening;
  • Have HEPA filtered downflow air drawn from laboratory or the outside air i.e., downflow air is not recirculated from the cabinet exhaust air);
  • Exhaust all inflow and downflow air to the atmosphere after filtration through a HEPA filter without recirculation in the cabinet or return to the laboratory ; and
  • Have all contaminated ducts and plenums under negative pressure or surrounded by directly exhausted (nonrecirculation through the work area) negative pressure ducts and plenums.
Type B2 cabinets may be used for work with volatile toxic chemicals and radionuclides required as adjuncts to microbiological studies.

Class III Bio-safety Cabinet:
A totally enclosed, ventilated cabinet of leak-tight construction. Operations in the cabinet are conducted through attached rubber gloves. The cabinet is maintained under negative air pressure of at least 0.50” WG (120 Pa). Downflow air is drawn into the cabinet through HEPA filters. The exhaust air is treated by double HEPA filtration or by HEPA filtration and incineration.
 
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