scope:

This part of ISO 21013 provides separate calculation methods fordetermining the required mass flow to be relieved for each of thefollowing specified conditions: ? vacuum-insulated vessels withinsulation system (outer jacket + insulating material) intact undernormal vacuum, outer jacket at ambient temperature, inner vessel attemperature of the contents at the specified relieving pressure; ?vacuum-insulated vessels with insulation system (outer jacket +insulating material) intact under normal vacuum, outer jacket atambient temperature, inner vessel at temperature of the contents atthe specified relieving pressure, pressure regulator of thepressure build-up system functioning at full potential; ? vacuum ornon-vacuum-insulated vessels with insulation system remaining inplace, but with loss of vacuum in the case of vacuum-insulatedvessels, outer jacket at ambient temperature, inner vessel attemperature of the contents at the specified relieving pressure orvacuum or non-vacuum-insulated vessels with insulation systemremaining fully or partially in place, but with loss of vacuum inthe case of vacuum-insulated vessels, fire engulfment, inner vesselat temperature of the contents at the specified relieving pressure;? vacuum-insulated vessels containing fluids with saturationtemperature below 75 K at 1 bar with insulation system remaining inplace, but with loss of vacuum with air or nitrogen in the vacuumspace; ? vacuum insulated vessels containing fluids with saturationtemperature below 75 K at 1 bar with insulation system remaining inplace, but with loss of vacuum with air or nitrogen in the vacuumspace with fire engulfment; ? vessels with insulation systemtotally lost and fire engulfment. Good engineering practice basedon well-established theoretical physical science needs to beadopted to determine the required mass flow where an appropriatecalculation method is not provided for an applicable condition.Recommendations for pressure relief devices for cryostats are givenin Annex A.