Enclosure fume cupboards

Partial enclosures are a compromise between containment and access. Most people misunderstand the function of partial enclosures. It is not possible to completely separate the interior from the surroundings with partial enclosures. Complete separation is only possible with total enclosures. The function of a partial enclosure is as dependent on the flow rate, the flow field, the working procedures, the contaminant generation process, etc. as is the function of exterior hoods. The advantage with a partial enclosure is that the physical walls diminish the possibilities for the contaminants to escape from the hood to the surroundings. Thus these hoods could be used when relatively high demands are put on the contaminant concentration outside the hood. Some of the most commonly used enclosures, such as fume cupboards and booths, are described. Many variations of these exist, e.g., enclosure of the complete process, and some of these are described here. 

It has long been recognized that the presence of a worker close to an enclosure, especially a fume cupboard, can have a significant effect on the exhaust hood performance (see Section 10.2.3.3). However, one aspect of... 

R. P. Harvey. In Proceedings of the Development and Use of Fume Cupboards, Fume Hoods and Ventilated Safety Enclosures in Laboratories . Symposium Organised by the Laboratory of the Government Chemist, London, March 1979, pp. 32-59. 

The practical approach to containment should be defense in depth, so a spill tray suitably lined with absorbent paper on a bench of suitable design and construction (raised edges/stainless steel or laminate) in a designated area would be suitable for very small quantities of nonvolatile material. As the activity and volatility of the material increase, the tray should be itself held within the partial containment provided by a ventilated fume cupboard or slit box. (The linear flow rate through any working aperture of a ventilated enclosure should be at least 0.5 m sec for nonvolatile materials and at least 0.75 m sec for volatiles such as iodine.) If there is an external radiation hazard as well as the potential for contamination, then appropriate shielding must be used but care should be taken not to disturb the enclosure air flows. (Checks should be made with a smoke generator if there is any doubt.)... 

By using extraction as close to the source of pollution as possible to minimise the escape of the pollutant into the atmosphere. The extraction devices can be either hoods, slots, enclosures or fume cupboards coupled to a system of ducts, fans and air cleaners. 

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