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 tested.