Many toxic industrial chemicals (TICs) such as chlorine and ammonia are stored as liquids at ambient temperature which flash when released to atmospheric pressure. Sponsored by the Chemical Security Analysis Center (CSAC) of the U.S. Department of Homeland Security, the Defense Threat Reduction Agency (DTRA) of the U.S. Department of Defense, and Transport Canada, the Jack Rabbit II tests were designed to release liquid chlorine at ambient temperature in quantities of 4,500-18,000 kg (5 to 20 T) to quantify the hazards of catastrophic release at scales represented by rail and truck transport vessels. All trials were conducted releasing chlorine through a 15.2 cm (6 in) circular breach in the 9,100 kg (10 T) capacity test vessel (disseminator) at different orientations (vertically downward, 45 degrees below horizontal, and vertically up). A final 18,000 kg (20 T) release was made vertically downward using a truck vessel. This article analyzes disseminator load cell data to determine the mass release rate. Along with this data, previously published data are also considered to quantify the impact on release rate of flash fraction and superheat limit temperature for various materials. This work develops a general approach to quantifying the mass release rate of flashing two phase releases of TICs and other flashing liquids such as cryogenics. (c) 2018 American Institute of Chemical Engineers Process Process Saf Prog 37:382-396, 2018