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RR881 - Investigation of the parameters that influence the effectiveness of a bench top partial enclosure

Bench top partial enclosures are frequently used in industry to control airborne contaminants. These hoods tend to be of basic design and often consist of nothing more than a box like structure with an open front to allow worker access and extraction at the rear to remove contaminated air. With this type of design the worker is forced to stand at the face of the enclosure and by doing so presents a blockage to the airflow that creates a ‘wake’ in front of the worker. Any release of contaminant into the recirculating wake region has the propensity to enter the worker’s breathing zone.

This aim of this study was to investigate the design parameters that influence the control effectiveness of an open fronted small partial enclosure. similar to those used in industry, and in particular to identify key variables of small partial enclosure design and to identify how key variables interact.

The results showed that eddies were created against all four walls of the enclosure. These interacted with the wake in front of the test manikin leading to contamination of the breathing zone. Reduction in the breathing zone of the manikin was best achieved by the addition of an offset flange to the entry of the enclosure. This design allowed air to enter between the flange and the enclosure walls and thus eliminated the wall eddies and consequently led to a reduction in the breathing zone concentration. The report also includes a number of other recommendations for design and use of partial enclosures.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

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Updated 2011-08-03