BS7989 SPECIFICATION FOR RE-CIRCULATORY FILTRATION FUME CUPBOARDS
July 15, 2020
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December 3, 2020
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FUME CUPBOARD TYPES, CONVENTIONAL? OR DUCTED?

There are two main types of fume cupboards, conventional and ducted - which you have will determine the type of filter you require, as would the size of the unit and the types of chemicals that are in use. ACF offer expert knowledge of all filter types and also their differing applications.

Ducted fume cupboards

These are fume cupboards whose exhaust is ducted to the outside atmosphere, usually via a stack/chimney whose height above roof level is designed to ensure full and proper dispersion of the fumes away from all areas where people might be affected. 

Within the ducted version there are a further three types.

- Constant Air Volume (CAV).

These are designed to maintain a constant air extraction volume no matter where the sash is positioned. Face velocities will vary depending on where the sash is set and will increase as the sash is closed. Air bypass openings situated near the sash ensure that changes in face velocity are kept within a specified range. 

Depending on design, fume cupboard sashes may move vertically, horizontally or in combination. 

- Variable Air Volume (VAV). 

These units use sash positioning controls to vary the fume cupboard extract fan speeds and subsequently alter the air extract volume. The extract volume varies depending on where the sash is positioned and allows face velocities to remain constant, at a predetermined level. The systems may be linked to building monitoring systems to enable extract and room make up air to be balanced. 

- Ducted, low flow fume cupboards. 

These fume cupboards are specially designed to maintain suitable containment at lower face velocities thus offering significant energy efficiency over standard systems. They typically operate with face velocities of 0.3 ms-1. 

Conventional fume cupboards

Ductless, re-circulating fume cupboards, these are self-contained units in which the exhaust air is passed through a filtration system and discharged back into the room. The filters must be matched to the class of chemicals to be used and have a limited absorbent capacity. Care must be taken to ensure this limit is not exceeded as it can result in the release of hazardous substances into the work environment. 

These units are unsuitable for work involving radioactive, highly toxic, carcinogenic or sensitising substances. It should be noted that HSE do not recommend using these fume cupboards for exposure control of vapours or carbon nanotubes (HSE Control Guidance note 201 and HSE Risk Management of Carbon Nanotubes 2009). 

The selection and fitting of recirculating systems must be carefully reviewed. Consideration should be given to whether such a unit can provide adequate, reliable control of the anticipated hazards and that the resources and a safe system of work.

Adequate regular checks should be made to ensure that the unit is operate within manufacturers specifications. If in any doubt guidance

should be sought from the Health and Safety Office. 

- Specialty Fume Cupboards. 

Other specialty fume extraction systems exist, which offer protection against specific hazards or classes of chemicals. These include acid digestion, water wash and scrubber systems. 

If you'd like to talk to an ACF specialist about filter types or number of filters for your fume cupboard, or you'd like to request a quote contact us info@absolutecarbonfilters.co.uk