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Microbiological Safety Cabinets

A microbiological safety cabinet (MSC) is a ventilated enclosure intended to offer protection, to the user and the environment, from aerosols generated when handling biological agents or material that may contain such agents.

There are 3 main types of safety cabinet. The correct safety cabinet for your work depends on a number of factors:

Class I

This is the traditional cabinet of microbiology and clinical diagnostic laboratories. Its construction is simpler than the other types and is therefore cheaper to produce and buy.  It works by drawing air into the cabinet away from the worker and then through a High Efficiency Particulate Air [HEPA] filter.  It is the cabinet of choice when the key requirement is the protection of the worker. 

Class II

These cabinets are designed so that the work area is kept clean by a down-flow of HEPA-filtered air across the work.  With good working technique it is possible to achieve both a high degree of product protection and a operator protection of the same order as that provided by Class I cabinets.  However, their performance is more affected by other factors, such as operator movement and air movements outside the cabinet.  They are typically used for cell and tissue culture applications and for other work where product protection from contamination is important. 

Class III

Class III cabinets are designed to completely contain the hazardous agent and are used mainly for work with hazard group 4 organisms or work with hazard group 3 organisms deemed to be at high risk, for example where highly concentrated samples are being handled.  They offer the greatest protection to the worker and work, but movements are more restricted and this may affect dexterity.

Laminar flow hoods

Laminar flow hoods should not be confused with MSCs!  These hoods provide a filtered air-flow which is intended for product protection only.  The cabinets must not be confused with Class II cabinets as they have no inflow, indeed the air passes over the product being worked on [e.g. cell culture] and so they offer no operator protection.  Therefore, laminar flow hoods must not be used with any biological material of human origin.  Other animal-derived material or tissue may only be used after a full risk assessment that confirms the total non-pathogenic and non-allergenic status of the material.  They also must not be used when handling biological agents [pathogenic organisms].


Microbiological Safety Cabinets are maintained in compliance with COSHH regulations and ACDP guidance according to the schedule described in the table below. The servicing of Inflow/Down flow cabinet capability may be increased to 6-monthly for Class II cabinets in CL2 laboratories if required following risk assessment.


Class I

Class II

Class III



Face Velocity/Inflow





Annually for CL2,

6-monthly for CL3

6-monthly for CL3 and CL4




In use OPFT

As required by assessment