Definitions of terms

Aerosol-generating procedure

High-risk procedures that may increase the potential for generating droplet nuclei as a result of the mechanical force of the procedure(for example, pipetting, vortexing, centrifuging or mixing).

Airborne transmission

The transmission of disease caused by dissemination of droplet nuclei that remain infectious when suspended in air.

Air changes per hour(ACH)

The number of laboratory room volumes of air expelled per hour and replaced with clean air.


A small room leading from one part of a laboratory into another part (for example, leading into a TB-containment laboratory).

Biosafety management plan

The use of a combination of administrative controls, containment principles, laboratory practices and procedures, safety equipment,emergency preparedness, and laboratory facilities to enable laboratory staff to work safely with infectious microorganisms.

Droplet nuclei

Dried-out residue of droplets <5 µm in diameter.

Expelled air (extraction)

Air removed from a laboratory and not recirculated.

Good microbiological technique

Good microbiological technique includes aseptic techniques and other practices that are not uniformly defi ned but are necessary to prevent contamination of the laboratory with the agents being handled and to prevent contamination of the work with agents from the environment.


Anything that has the potential to cause harm, regardless of how likely or unlikely such an occurrence might be.

Hybrid ventilation

A combination of both mechanical and natural ventilation (also called mixed-mode ventilation).

Infectious aerosol

A particulate suspension of infectious agents that has the potential to be inhaled and cause infection.

Laboratory coats

Laboratory coats usually have long sleeves and fasten in the front. These should be worn when working in settings where there is a low risk or moderate risk of tuberculosis (TB).

Laboratory gowns

These gowns should be long sleeved with an elasticised cuff (at least 30mm long) and fasten at the back. Different sized gowns should be available for staff. Gowns should be used when staff work in settings where there is a high risk of TB. When the laboratory technician is standing, the gown must extend below the height of the workbench; the gown should fully cover the technician’s lap when he or she is sitting.

Natural ventilation

The use of natural forces to introduce and distribute outdoor air into and out of a laboratory.

Mechanical ventilation system

A mechanical ventilation system uses an exhaust fan to extract air from the laboratory.


A plenum is a space in the upper section of a biological safety cabinet where a portion of the air is exhausted from the cabinet and the remainder supplied to the work area.


A combination of the likelihood and consequences of an event related to a specific hazard.

Risk assessment

The process of evaluating the risk or risks arising from a hazard or hazards, taking into account the adequacy of existing control measures; the process also includes deciding whether the risk is acceptable.


A process that kills all classes of microorganisms and spores.


Ventilation brings outdoor air into a building or a laboratory room and distributes air through the laboratory. For biosafety measures,the purpose of ventilation in buildings is to provide healthy air for breathing by diluting with clean air any potential aerosols generated in the laboratory, and by providing an airfl ow rate that exchanges air at a given rate.

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