Microbiological safety cabinets (MSC)
Class II Microbiological safety cabinets should be used when aerosols are likely to be generated. Experiments involving some types of specified material may generate airborne particles which may lead to release/escape from a quarantine station/confinement facility. This is most likely to occur with sporulating plant pathogenic fungi and plant pathogenic bacteria (e.g. Streptomyces spp.) but may also apply to work on soils if aerosols (including dust) are likely to be produced. In such cases the work will need to take place in a Microbiological Safety Cabinet (MSC). In some instances, there may be acceptable alternatives which mean a MSCII would not be required. If a MSCII is not feasible you should contact Defra.
MSCs are divided into three classes, Class I, Class II and Class III, with Class III cabinets offering the highest technical specifications. All three classes of cabinet are designed to offer protection to the worker at the cabinet as well as to the wider environment by filtering all exhaust air to an appropriate level before it is discharged. The higher specification MSCs also offer levels of protection for the work from external contamination. However, MSCs are not designed to contain radioactive, toxic or corrosive substances. See table 3 for more details.
Class II cabinets are the most appropriate for work involving specified material or pest(s), however Class III cabinets should be used when there is a risk of vigorous aerosol generation. Class I cabinets are not suitable for use with specified material or pest(s).
Air flowing into Class II cabinets can be disturbed by sudden movement outside of the cabinet and consequently cabinets should not be located in rooms used as passageways, opposite doors or windows or close to ventilation ducts.
Air discharged from Class II and III cabinets is passed through a HEPAfilter before discharge. The exhaust air should be discharged to the outside by a dedicated extraction system or recycled back into the laboratory. Recycled air must pass through two independently tested filters. Filters should be changed when the air pressure falls below 0.75 m/s and must be disinfected before removal and disposed of as per the requirements of the scientific authorisation. The entire MSC should be disinfected regularly, with chemical disinfectants. Many MSCs come with UV disinfection system’s built in, this cannot be relied on for disinfection of specified pest(s), therefore chemical disinfection should also be used.
All cabinets must conform to all relevant British and EU standards and should be tested regularly for compliance. Amongst other things this states that:
- All interior work surfaces shall be made of corrosion resistant material, have a uniform finish and be free of cracks
- All joints should be sealed with a recommended sealant
- If a solid working floor area is used, it shall be liquid-tight with a raised edge at least 10mm in height. If the floor is perforated, a subfloor should be used to trap spilt liquid and should be liquid-tight with a raised edge of at least 10mm in height all round. Perforated floors shall be removable to allow cleaning
- Air filters should be mounted in such a way that no air can bypass the filter medium. When the cabinet exhaust is ducted to the atmosphere the cabinet shall be fitted with an automatic anti-blowback system downstream of the filters to prevent air blowing back into the cabinet.
In a limited number of cases, mainly some types of research involving soils, it may be acceptable to use an alternative type of safety cabinet such as a Waysafe 2. However, all requests to use alternative safety cabinets need to be considered by Defra before approval for their use can be granted.
Note: LAMINAR FLOW CABINETS are routinely used in laboratory studies involving fungi and bacteria, but it must be stressed that these are not MSCs and do not afford any level of environmental protection. Airborne particles associated with any work taking place in a laminar flow cabinet will be actively liberated into the atmosphere by the air stream which is not filtered at the exhaust. These cabinets should not be used for work involving specified material or pests where the dissemination of airborne particles is a possibility.
Secondary containment of quarantine organisms within cages
This may be necessary in certain situations when there is a need to restrict the potential spread within a quarantine station/confinement facility. This is particularly applicable for mobile plant pests and when plant pollen needs to be contained. The use of secondary containment may also be required to keep out invertebrate vectors of plant pathogens or where the deliberate vectoring of viruses is intended and the invertebrates themselves require containing. Whenever caging is considered necessary, it should be of appropriate design and construction for the material or organisms in question.
Plant pots/containers
Plants in association with specified pests must be grown in suitable containers. Where there is the requirement to re-use containers in future experiments, they should be composed of a material capable of preventing penetration by plant roots, and which can be easily disinfected.
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