Section 18(2)(ia) in The Static and Mobile Pressure Vessels (Unfired) Rules, 2016
(ia)for cryogenic pressure vessels, the outer vessel shall be provided with a vacuum valve and safety relief device (disc) to release internal pressure. The discharge area of such device shall be at least 0.34 sq.mm/litre of water capacity of the inner vessel but not exceeding 5000 mm2. The relief device shall function at a pressure not exceeding the internal design pressure of the outer vessel;