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Investigation of the Parameters that Influence the Effectiveness of an Open Fronted Enclosure

C. J. Saunders and S. Bennett, 2013
enclosure | tracer gas | containment | local exhaust ventilation | LEV | extraction
Bibliographic info: The International Journal of Ventilation, Vol. 12 N°2, September 2013
Languages: English

Open fronted ventilated enclosures are commonly used in industry to control worker exposure to a wide range of chemicals. These enclosures 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. This design forces the worker to stand at the face of the enclosure and by doing so presents a blockage to the airflow.

The aim of this experimental study was to investigate design parameters that influence the control effectiveness of small ventilated partial enclosures. All experimental work was carried out in a purpose built, free standing, partial enclosure with and without a manikin present. Sulphur hexafluoride (SF6) was used as the test gas and released via two different designed ejectors inside the enclosure. Air samples were taken in the breathing zone of the manikin and the SF6 concentration measured. Two different rear baffles and four flanges, which were fitted to the opening of the enclosure, were tested at face velocities between 0.3 and 0.7 ms-1.

The presence of a manikin at the face of the enclosure caused a ‘wake’ region of highly turbulent air to form in front of it. This ‘wake’ interacted with the eddy against the floor of the enclosure. Of the four flanges tested only one, which allowed air to pass between the wall of the enclosure and the flange, significantly reduced the concentration of SF6 in the breathing zone of the manikin. This flange was considered to be the most practical design for small partial enclosures.

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