Section 179.500-12 - Pressure relief devices(a) Tank shall be equipped with one or more pressure relief devices of approved type and discharge area, mounted on the cover or threaded into the non-marked end of the tank. If fittings are mounted on a cover, they shall be of the flanged type, made of metal not subject to rapid deterioration by lading or in service. Total flow capacity shall be such that, with tank filled with air at pressure equal to 70 percent of the marked test pressure of tank, flow capacity will be sufficient to reduce air pressure to 30 percent of the marked test pressure within 3 minutes after pressure relief device opens.(b) Pressure relief devices shall open at a pressure not exceeding the marked test pressure of tank and not less than 7/10 of marked test pressure. (For tolerance for pressure relief valves, see § 179.500-16(a) .)(c) Cars used for the transportation of flammable gases shall have the safety devices equipped with an approved ignition device.Amdt. 179-32, 48 FR 27708, June 16, 1983, as amended at 66 FR 45391 , Aug. 28, 2001; 68 FR 57634 , Oct. 6, 2003