This part of ISO 21013 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. — Vessels with insulation system totally lost and fire engulfment. Good engineering practice based on well-established theoretical physical science shall be adopted to determine the required mass flow where an appropriate calculation method is not provided for an applicable condition.