This part of ISO 4126 specifies the sizing of safety valves and bursting discs for gas/liquid two-phase flow in pressurized systems such as reactors, storage tanks, columns, heat exchangers, piping systems or transportation tanks/containers. The possible fluid states at the safety device inlet that can result in two-phase flow are given in Table 1. NOTE The expression safety valve is a synonym for valves as described in ISO 4126-1, ISO 4126-4 and ISO 4126-5. The expression bursting disc is a synonym for bursting disc safety device as described in ISO 4126-2, ISO 4126-3 and ISO 4126-6.