Biological Safety Cabinet

Absolute Containment – Capacity for completely retaining any specified substance. (In the present sense, the specified Class III safety cabinet is an example.)
Aerosol – A colloid of liquid or solid particles suspended in a gas, usually air.
Agent – Any biological, chemical or physical power, principle or substance capable of acting upon a subject organism, usually to its detriment.
Air Balance – Meaning, as it applies to Class II cabinets, to adjust airflow volume so that air exhaust is equal to air intake and thereby eliminating (or minimizing) movement of outside air into the cabinet work area and vice versa through the face opening.
Air Barrier (“air curtain”) – The unidirectional movement of air past and parallel to the plane of an opening, and at a velocity greater than that on either side, thereby creating an impedance to transverse movement of airborne particulates through the opening.
Air Stream – A current of air; airflow.
Aseptic Technique – The performance of a procedure or operation in a manner that prevents the introduction of septic material.
Bag In, Bag Out – A method of introducing and removing items from a contaminated enclosure that prevents the spread of contamination or opening of the contaminated space to the atmosphere through the use of plastic bagging material.
Biohazard – A contraction of the words biological and hazard: infectious agent(s) presenting a real or potential risk to the well-being of man, other animals, or plants, either directly through infection or indirectly through disruption of the environment.
Biological Safety Cabinet – Cabinet intended to protect the user and environment from the hazards of handling infected material and other dangerous biological material but excluding radioactive, toxic and corrosive substances. Any air discharged to the atmosphere shall be filtered. Some types may also protect the material being handled in them from environmental contamination.
Biosafety Level – Four biosafety levels (BSL 1, 2, 3, or 4), consist of combinations of laboratory practices and techniques, safety equipment and laboratory facilities. Each combination is specifically appropriate for the operations performed, the documented or suspected routes of transmission of the infectious agents and for the laboratory function or activity.
Brownian Motion – A random movement of microscopic particles suspended in liquids or gases resulting from impact of the molecules of the suspending agent on the particles.
Cabinet Certification – Measurement and/or correction of safety cabinet air velocities, patterns, balance, leakage and filtration system efficiency by a qualified technician after which the unit meets standard specifications.
Cabinet Classification
Class I: A ventilated cabinet for personnel and environmental protection which may be operated with an open front, or with a gloveport panel in place, with or without gloves attached. The cabinet exhaust air may be filtered through a HEPA and/or charcoal filter before being discharged to the outside atmosphere. This cabinet is suitable for work with low and moderate risk biological agents where no product protection is required.
Class II: (Formerly called laminar flow biological safety cabinet), a ventilated cabinet for personnel, product and environmental protection having an open front with inward airflow for personnel protection and a mass recirculated HEPA-filtered airflow for product protection. The cabinet exhaust air is filtered through a HEPA filter for environmental protection. This cabinet is suitable for work with low to moderate risk biological agents. Vapors or gases which are hazardous from a toxic, radioactive, or flammability standpoint should not be used in cabinets which recirculate all or part of the air. Consideration of use of such materials should be evaluated carefully from the standpoint of build-up to dangerous levels and problems of decontamination of the cabinet.
Class III: A closed front ventilated cabinet with negative pressure of gas-tight construction providing total protection for personnel and product from contaminants exterior to the cabinet. Supply and exhaust air is suitably treated to protect the environment. This cabinet, fitted with rubber gloves, provides the highest containment reliability of these three classes and is utilized for all activities involving high risk agents.
Clean Room – A dust-free facility.
Containment – Prevention of agent transmission from one point to another (primary, secondary, absolute, partial, total).
Contamination – Any foreign substance which makes an unwanted incursion. In the present context, usually viable airborne particulates.
Control Velocity – The air velocity at the face of an enclosing hood to retain a contaminant generated within the hood.
Decontamination – The destruction or removal of living organisms (this does not imply either total destruction or total removal) or the removal or neutralization of toxic agents or chemical carcinogens.
Diffuser – A device used to distribute or direct airflow.
DOP – Dioctyl phthalate, an oil that can be aerosolized to an extremely uniform size; i.e., 0.3 µm (micrometer) for a major portion of any sample; the aerosol is used to challenge HEPA filters.
“Hot” DOP – Produced by controlled vaporization and condensation of liquid DOP to give a cloud of monodisperse droplets with diameters of approximately 0.3µm (micrometer).
“Cold” DOP – Produced by compressed air atomization of room temperature liquid DOP, aerosol size 0.3 to 3.0 µm (micrometer) with a mean diameter of 0.7 µm (micrometer).
Exhaust – The withdrawing and expelling of air from the cabinet by means of a blower or fan; that portion of the cabinet air that is discharged after filtration, either to the room or into a ventilation system.
Face Velocity – Air velocity at the cabinet work opening, velocity of the air entering the cabinet at the work opening.
Filter Efficiency – The efficiency of various filters can be established on the basis of entrapped particles; i.e., collection efficiency; or on the basis of particles passed through the filter; i.e., penetration efficiency.
Filter Penetration – The passage of particles through a filter without removal from the air stream.
Foot-candle (fc) – The unit of illumination when the foot is taken as the unit of length. It is the illumination on a surface one square foot in area on which there is a G
Glovebox – A sealed enclosure in which all handling of items inside the box is carried out through long rubber or neoprene gloves sealed to ports in the walls of the enclosure. The operator places his hands and forearms in the gloves from the room side of the box so that he is physically separated from the glovebox environment but is able to manipulate items inside the box with relative freedom while viewing the operation through a window.
Hard Ducting – Permanently installed ductwork not intended to be disassembled for normal cabinet servicing or testing.
HEPA Filter – High Efficiency Particulate Air filter. A disposable, extended-pleated, dry-type filter with (1) a rigid casing enclosing the full depth of the pleats; (2) a minimum particle removal efficiency of 99.97% for thermally generated monodisperse DOP smoke particles with a diameter of 0.3 µm (micrometer); and (3) a maximum pressure drop of 1 in. w.g. when clean and operated at its rated airflow capacity.
High Efficiency Filter – A filter that provides 90% efficiency against 1 micrometer diameter particles in accordance with the current edition of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) Specification 52.
High Efficiency Particulate Air Filter – See HEPA filter.
High Risk (biosafety level 4) – Risk level of agents and/or operations requiring additional control measures beyond those for moderate risk. These are agents or operations with various dangerous combinations of the following characteristics:
(1) low infective doses for personnel, animals or plants; (2) high concentrations: (3) release of microbial aerosols: and (4) genetic alteration or recombination that significantly increases potential pathogenicity or virulence.
High Velocity Return Air Slots – Unique Baker Company devices which help to prevent escape or entry of particulates at the front access opening, or behind the viewscreen.
Horizontal Laminar Airflow – An essentially unidirectional airflow with minimum turbulence, leaving a vertically-mounted filter and flowing parallel to the work surface.
Horizontal Laminar Flow Bench – A ventilated cubicle with solid sides having a table-height work surface and unidirectional, minimum turbulence air entering from a vertically mounted high efficiency filter at one side and leaving the cubicle at the opposite (open) side.
Inches of Water Gauge (in. w.g.) – A unit of pressure equal to the weight of a column of liquid water one inch high at 20° C (1 in. w.g.=0.036 psi).
Inertial Impaction – A HEPA filtration phenomenon by which 5 µm (micrometer) or larger particles being carried by the airflow cross air stream lines and are retained on the filter fiber.
Interception – A HEPA filter phenomenon by which particles larger than 0.3 µm (micrometer) contact a filter fiber and are retained by it.
Laboratory-Acquired Infection – Any infection resulting from exposure to biohazardous materials in a laboratory environment. Exposure may be the result of a specific accident or inadequate biohazard control procedure or equipment.
Laminar Airflow – Generally defined as airflow in which the entire body of air within a confined area moves in essentially unidirectional velocity along parallel flow lines. Laminar airflow is technically defined as fluid flow in which its velocities are free of macroscopic fluctuations which generally occur when the Reynolds number is less that 2000 (Reynolds number is the ratio of inertial to vicous forces in a pipe or duct).
Leaktightness – The condition of a system, unit or component where leakage through its pressure boundary is less than a specified maximum value at a specified pressure differential across the pressure boundary.
Low Risk (biosafety level 2) – Risk level of agents and/or operations having minimal effect on personnel, animals or plants under ordinary use.
Manometer – An instrument for measuring pressure that is usually constructed from a transparent U-tube and partially filled with a liquid such as water, mercury or oil. The relative amount of displacement of the liquid between the two legs of the U indicates the excess of pressure being exerted on one side or the other.
Microbiological Aerosol Test – Testing conducted on biological safety cabinets to ensure performance standards.
Micrometer – A unit of length equivalent to 10-6 meters or 10-3 millimeters. Symbol µm.
Moderate Risk (biosafety level 3) – Risk level of agents and/or operations requiring special conditions for control or containment because of (1) known pathogenicity to personnel, animals or plants; (2) concentration; or (3) genetic alteration with other materials.
Nanometer – Unit of wavelength equal to 10-9 meter.
Negative Pressure – Pressure in a space which causes an inflow of air.
Orifice Meter – A restriction in a pipe between two pressure taps; by attaching a pressure gauge the airflow can be determined.
Partial Barrier – An enclosure constructed so that contamination between its interior and its surroundings is minimized by the movement of air.
Partial Containment – An enclosure which is so constructed that contamination between its interior and the surroundings is minimized by the controlled movement of air. Class I and Class II safety cabinets are examples. Means that a small percentage of the aerosol in the cabinet (usually less than 0.0001% to 0.01%) can escape into the laboratory. In many cases, it takes a significant number of organisms, say 1,000 or more, to cause an infection so the escape of a very small number is allowable.
Performance Envelope – The range of airflow parameters within which a biological safety cabinet will pass the standard microbiological aerosol tests.
Permissible Exposure Limits – The time-weighted average limit and ceiling limit established by OSHA for regulated toxic substances which pose a potential occupational carcinogenic risk to workers.
Photometer – Instrument used for measuring the concentration of DOP smoke particles up and downstream of a HEPA filter.
Physical Containment – A term that describes those methods used in microbiology to contain infectious agents in the environment where the agent is being handled or maintained.
Pitot Tube – A standard velocity meter, an L-shaped device consisting of two concentric tubes, when inserted vertically into an air stream, one tube measures total pressure, the other static pressure. When connected across a manometer, the difference between these pressures, the velocity pressure, is indicated. The velocity pressure can be used to compute the velocity of the air stream.
Plenum – An enclosure for flowing gases in which the static pressure at all points is relatively uniform.
Positive Pressure – Pressure in a space which causes an outflow of air.
Primary Containment Device – An engineering system, a fully closed container or a laboratory-type hood which is designed to contain hazardous materials so as to reduce or eliminate the potential for worker exposure to the contained hazardous materials.
Protection (Class II cabinets)
Environmental Protection – Means that any aerosol generated within the unit is removed from the air or deactivated (such as by incineration) before the air from the cabinet is discharged either inside or outside the facility.
Personnel Protection – Means that any aerosol generated within the cabinet is kept away from the face of the technician doing the work.
Product Protection – Means that the air at the work surface of the cabinet has been filtered so that it is free of airborne particles and organisms which could contaminate the work.
Risk Assessment – The process of obtaining qualitative or quantitative measures of risk levels, identifying possible health effects, environmental effects and any other consequences as well as the degree of uncertainty in those estimates.
Risk Identification – Designation of the nature of the risk, source, manipulation, consequences.
Risk Source Characterization – Description of the characteristics of the risk source that have the potential for creating or increasing the risk.
Set Point – The optimal operating settings for a biological safety cabinet determined by airflow velocity readings.
Static Pressure – The pressure of a fluid exerted in all directions equal and opposite to the pressure tending to compress the fluid. In ventilation applications, static pressure is usually the difference between the absolute pressure in an exhaust system and atmospheric pressure, such that static pressure less than atmospheric pressure is termed “negative static pressure” and static pressure above atmospheric pressure is termed “positive static pressure.” (The tendency to either burst or collapse the pipe.)
Sterile – The absence of all life on or in an object. This is an absolute term; there can be no such description as “nearly sterile,” “partially sterile,” etc.
Sterilize – Any process, physical or chemical, which results in the absence of all life on or in an object, applied especially to microorganisms, including bacteria, fungi and their spores, and the inactivation of viruses.
Supply Air – Air entering the cabinet through the work opening to make up for the volume of air exhausted. In Class II cabinets this air passes through the supply HEPA filter before moving vertically over the work surface.
Thermo-Anemometer – An instrument for measuring air velocity based on the removal of heat from a sensor as the air passes it.
Thimble – A connection between a cabinet exhaust outlet and the facility exhaust system through which room air may pass.
Total Containment – Means that no escape of aerosol is permitted. This is required for highly infectious or extremely dangerous agents.
Total Pressure – The algebraic sum of static and velocity pressures.
Toxic – Having an adverse physiological effect on biological systems.
Transition – A change in the cross-sectional area or shape of a duct or hood.
Triac Speed Controller – Solid-state device which can be adjusted to vary the AC voltage at the output through a range from essentially zero up to full line voltage.
Ultraviolet (UV) Radiation – Denoting the short wavelengths of light beyond the violet end of the visible spectrum.
Upstream – The direction opposite to the flow.
Velocity – A vector that specifies the time rate of change of displacement; i.e., the first derivative of the displacement with respect to time.
Velocity, Capture and/or Containment Velocity – The velocity necessary to capture or contain a generated contaminant; in a hood this usually ranges from 50 to 200 FPM.
Velocity Pressure – The kinetic pressure in the direction of flow necessary to cause a fluid at rest to flow at a given velocity. Velocity pressure is always positive and is exerted in the direction of airflow.
Vertical Laminar Airflow – An essentially unidirectional airflow with minimum turbulence, from the top of a biological safety cabinet work area downward to the work surface.
Vertical Laminar Flow Bench – A ventilated cubicle with solid sides having a table-height work surface and essentially unidirectional minimum turbulence airflow entering from a horizontally mounted high efficiency filter at the top and leaving the cubicle through an access opening at the bottom of the front side.
Viable – Literally, “capable of life.” Generally refers to the ability of microbial cells to grow and multiply as evidenced by, for example, formation of colonies on an agar culture medium, or, as with viruses, to divert the host cell’s metabolism to replications of the parasite. Frequently organisms may be viable under one set of culture conditions and not under another set, making it extremely important to define precisely the conditions used for determining viability.
Virus – A term for a group of microbes, which, with few exceptions, are capable of passing through fine filters that retain bacteria; they are incapable of growth or reproduction apart from living cells.
Zoned Airflow – A Baker Company patented design feature in which the airflow velocity is greater behind the viewscreen than over the work surface, increasing the cabinet’s containment capabilities.