An employee was going upstairs to open a process valve to vent a chlorinator; another employee was massaging the plugged down leg on the chlorinator. The plug broke free and dumped titanium tetrachloride into a sump. This caused a chemical reaction that resulted in overpressure in the sump, whose vent line failed in three places. Both employees inhaled titanium tetrachloride gas and developed upper respiratory distress. They were hospitalized.