Provides separate calculation methods for determining the required mass flow to be relieved for each of the following specified conditions. - vacuum-insulated vessels with insulation system (outer jacket + insulating material) intact under normal vacuum; - outer jacket at ambient temperature; inner vessel at temperature of the contents at the relieving pressure. - vacuum-insulated vessels with insulation system (outer jacket + insulating material) intact under normal vacuum; - outer jacket at ambient temperature; - inner vessel at temperature of the contents at the relieving pressure; - pressure regulator of the pressure build-up system functioning at full potential; - vacuum-insulated vessels with insulation system remaining in place but with loss of vacuum, or non-vacuum-insulated vessels with insulation system intact; - outer jacket at ambient temperature; - inner vessel at temperature of the contents at the relieving pressure; - vacuum or non-vacuum-insulated vessels with insulation system remaining fully or partially in place, but with loss of vacuum in the case of vacuum insulated vessels, and fire engulfment; - inner vessel at temperature of the contents at the relieving pressure.