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Fume Cupboards

The use of engineering controls to remove dusts, vapours, fumes etc., away from the breathing zones of those working with materials, must always be considered a higher priority during the risk assessment process over the provision of personal protective equipment. Engineering controls include the likes of fume cupboards, glove boxes, fume hoods, fume capture device and other type of extraction systems. Dependent upon the activities to take place in a laboratory a number of different types of system may be needed to manage the risks.

Fume cupboards will either need ducts, where fans remove hazardous fumes from the laboratory and discharge them to atmosphere, or filters which remove fumes and recirculate the air back to the laboratory. Whilst the latter is cheaper to buy, the running costs are often much higher, which may make them more expensive in the long term.

Not everything can simply be vented to atmosphere. Environmental legislation may apply which prohibits emissions from being discharged. The chemical types and volumes will be important criteria at the design stage to determine whether some form of filtration or scrubber unit will need to be fitted prior to the discharge point, whether sampling points need to be incorporated into the ductwork, and/or whether the duct (fan and ancillary equipment) needs to be fire retardent, resistent to certain acidic emissions or designed to prevent sources of ignition.

It is therefore important to engage a suitably qualified local exhaust ventilation design engineer when looking at installing local exhaust ventilation systems like those stated above or when re-designing an existing system.

A wrongly sized duct may lead to the transport velocity being insufficient which can cause contaminants to settle out in the ducting. This can be a serious fire hazard if combustible or flammable contaminants are being extracted. If flammable vapours/materials are being extracted but no consideration has been given to the prevention of a source of ignition or to dilution well below the lower explosion limit, a fire could occur. Poor design of the exhaust point can cause the contaminants to be captured by the air supply system and then, instead of being exhausted and diluted, they may enter a downdraught caused by adjacent buildings and re-enter the workplace. An undersized extract fan system will lead to the hood not containing or capturing the contaminants sufficiently. It should never be assumed that everything can simply be discharged into an existing duct.

The chemical types and volumes will similarly need to be known (or estimated), when considering whether a recirculating fume cupboard is preferable. The filter(s) will need to be suitable for the chemical types in use. If large volumes of volatile organic materials are to be used, for example, it is worth bearing in mind that the filter will require regular replacement once installed. A recirculating cupboard is therefore only really favourable when the work involves small volumes of volatile materials, the work is of lower hazard, or it is only infrequently used.

The siting of any fume cupboard will be critical in terms of its operational effectiveness. Any area prone to draughts will cause interference with the flow of air through the fume cabinet and could expose the person to any chemicals that they are working with. Siting of fume cupboards is therefore a critical part of the facility design and should only be designed and commissioned by competent local exhaust ventilation engineers.

All of these extraction systems are subject to statutory testing under the Control of Substances Hazardous to Health (COSHH) Regulations and must be installed by specialist competent persons and placed on the statutory inspection and testing register held by Estates upon their installation.

Those engaged to provide advice and guidance in the design of the fume cupboard extraction system will need information on the typical types of chemicals to be discharged in order to design an appropriate system for the laboratory space, or to consider whether an existing system can cater for the chemicals to be used.