This International Standard covers the normal and emergency vapour venting requirements for aboveground liquid petroleum or petroleum products storage tanks and aboveground and underground refrigerated storage tanks@ designed for operation at pressures from full vacuum through 103@4 kPa (ga) [15 psig]. Discussed in this International Standard are the causes of overpressure and vacuum; determination of venting requirements; means of venting; selection@ and installation of venting devices; and testing and marking of relief devices. This International Standard is intended for tanks containing petroleum and petroleum products but it can also be applied to tanks containing other liquids; however@ it is necessary to use sound engineering analysis and judgment whenever this International Standard is applied to other liquids. This International Standard does not apply to external floating-roof tanks.