30 CFR § 18.28 Devices for pressure relief, ventilation, or drainage.
(a) Devices for installation on explosion-proof enclosures to relieve
pressure, ventilate, or drain will be acceptable provided the length of the
flame-arresting path and the clearances or size of holes in perforated metal
will prevent discharge of flame in explosion tests.
(b) Devices for pressure relief, ventilation, or drainage shall be
constructed of materials that resist corrosion and distortion, and be so
designed that they can be cleaned readily. Provision shall be made for secure
attachment of such devices.
(c) Devices for pressure relief, ventilation, or drainage will be
acceptable for application only on enclosures with which they are explosion
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