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Microbiological Safety Cabinets msc

Microbiological Safety Cabinets (MSCs, or MBSCs) are intended for work with biological agents, including pathogenic micro-organisms; genetically modified micro-organisms; cell cultures and human or animal tissues and fluids. There are three classes of Safety Cabinet – Class I, Class II and Class III.

Class I cabinets are open fronted units which continuously draw air into the cabinet and out through a HEPA* filter, providing protection for the user but offering no product protection. They are suitable for use with hazard group 1, 2 or 3 organisms, subject to risk assessment.

Class II cabinets are similar in design to Class I cabinets, but protect the working area from external contamination as well as protecting the operator. Inward air is directed downwards and below the work surface, HEPA filtered and then redirected back into the work area as a laminar down flow of clean air.  The balance of this laminar down flow with the incoming air provides an air curtain to ensure operator protection. They are suitable for use with hazard group 1, 2 or 3 organisms, subject to risk assessment.

Class III cabinets are totally enclosed units in which operations are conducted through gloves attached to glove ports. Air enters and leaves the cabinet through a HEPA filter. They offer maximum operator and product protection and are suitable for work with organisms of all hazard groups, including group 4.

Most cabinets will be labelled as to their Class. If there is no label, you should be able to tell the class by looking inside the cabinet.  Class I cabinets have a solid working space; Class II cabinets have a grille at the front of the working space where air is drawn into the cabinet before being recirculated down over the working area. The working space itself may also be perforated.

As with fume cupboards, Microbiological Safety Cabinets can be ducted or recirculating. Ducted cabinets will have a large exhaust duct sited at the top of the cabinet and extract air out of the building. Recirculating cabinets have no ducts but filter and re-circulate air back into the room. The filter plays a crucial role and therefore special considerations must be made:

  • Selecting the correct type of filter
  • Timely replacement and disposal of filters using a safe method – make sure you know the life span of the filter and ensure an expiry date is indicated

A risk assessment should be undertaken to determine the Class of cabinet appropriate for a particular work activity. This should take into account the nature of the potential hazards in terms of the micro-organisms involved and their route of infection, and also the techniques to be carried out and whether protection of samples is needed.

Siting of safety cabinets within a laboratory
Before installing a safety cabinet, ensure that you have checked that there is adequate space for a cabinet to work properly in everyday use. Air currents and the movement of people in the laboratory can adversely affect the cabinet’s performance. Avoid siting cabinets near windows, doors, walkways, air diffusers, air conditioning units or adjacent to any fridge and incubator doors.

Use of bunsen burners
Bunsen burners and other naked flames should not be used in microbiological safety cabinets. As well as being a fire risk and potentially damaging filters, they will disturb air-flows inside the cabinet and could result in contaminated air escaping into the laboratory.

If burners are required, they must be low profile microburners equipped with a lever control to give full flame only as required, in order to minimise disturbance and used in Class I cabinets only. The burner should be placed towards the back of the cabinet away from any activity and the gas flow should be set at its lowest feasible level.

Fumigation Advice

*HEPA = High-efficiency particulate air; a type of air filter capable of filtering very small particles and commonly used in work with biological agents




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