Air velocity in exhaust ventilation systems for power-ventilated enclosures, where, as stated in Sentence 5.5.4.2.(1):

• the use of the dangerous goods releases flammable vapours, or causes runaway or potentially explosive reactions,
• liquids are heated to a temperature equal to or greater than their flash point, or
• Class I liquids or unstable liquids are used.

This applies to laboratories where dangerous goods, including flammable liquids and combustible liquids, are used in normal laboratory operations in quantities or in a manner that creates a fire or explosion hazard.

This also applies where perchloric acid is heated above normal ambient temperature, as stated in Sentence 5.5.5.5.(1).

To limit the probability that combustible or reactive deposits will accumulate, which could lead to an increase of the combustible content and fire severity, which could lead to the spread of a fire in the laboratory to other parts of the building, which could lead to harm to persons.

To limit the probability that combustible or reactive deposits will accumulate, which could lead to obstruction of the ventilation system and reduction of its exhaust capacity, which could lead to an explosive atmosphere, which in the presence of a source of ignition could lead to a fire or explosion, which could lead to harm to persons.

To limit the probability that combustible or reactive deposits will accumulate on the blades of the exhaust fan, which could lead to its misalignment or improper operation, which could lead to the generation of sparks or heat and the ignition of deposits or explosive vapours or mists, which could lead to a fire or explosion, which could lead to harm to persons.