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If the sash is closed, the flow rate for regulated fume hoods (variable air volume flow – VAV) may be lower, which can increase the explosion hazard due to the lower purging rate. There is then a risk of injury resulting, for example, from crushing.

Information pertaining to the air volume of a fume hoods related to a unit of length, for example related to 30 cm, is to be requested from the manufacturer.

See also DIN EN 294 “Sicherheit von Maschinen; Sicherheitsabstände gegen das Erreichen von Gefahrstellen mit den oberen Gliedmaßen“ (now: DIN EN ISO 13857 “Sicherheit von Maschinen – Sicherheitsabstände gegen das Erreichen von Gefährdungsbereichen mit den oberen und unteren Gliedmaßen“).

The company Tintschl used a numerical simulation calculation to demonstrate that at least 200 air changes are required to avoid additional fire and explosion hazards in a fume hood (900 mm worktop level) with regard to the volatility of the worst case among the common laboratory solvents, diethylether.

See also company Tintschl presentation of the results in the Standard Committee "Abzüge und Laborlufttechnik" (32).