Fume hoods must be designed in such a way that, when they are operating, their structure and ductwork:
- prevent gases, vapors and dusts in hazardous concentrations or quantities from entering the laboratory from inside the fume hood
- prevent hazardous explosive atmospheres from forming inside the fume hood
- protect insured persons from splashing hazardous materials or flying broken glass.
It must be borne in mind that the containment capacity of fume hoods may change in an unpredictable way in the event of major thermal stresses. Enclosures and workplaces with extraction systems are not fume hoods because they do not achieve some of the above-mentioned protection objectives. For certain work, however, the hazard assessment may indicate that they provide an adequate level of protection.
Variable air volume (VAV) fume hoods and fume hoods with automatic night setback have to be clearly labelled as such for users, for example by means of an adhesive label.
It is advisable to provide a switch on a variable volume flow control fume hoods where the flow rate is regulated so that a higher rate can be set in the event of an accident happening when the sash is lowered.