Abstract: AT ABOUT 9:30 PM ON OCTOBER 10, 1986, A WATER TREATMENT OPERATOR (EMPLOYEE #1) OPENED THE DOOR TO A CHLORINATOR ROOM DURING FLOOD CONDITIONS. AN ELECTRICAL SHORT CIRCUIT CAUSED THE CHLORINATOR TO CONTINUE RUNNING AFTER THE WATER FLOW HAD STOPPED. THE HIGH CONCENTRATION OF CHLORINE IN THE TREATMENT CIRCUIT LINE CORRODED A COPPER PIPE IN THE CHLORINATOR ROOM. THIS RESULTED IN WATER WITH A HIGHER THAN USUAL CONCENTRATION OF CHLORINE BEING SPRAYED AROUND THE ROOM FROM HOLES IN THE PIPELINE. EMPLOYEE #1 THEREFORE INHALED A HIGHER CONCENTRATION OF CHLORINE THAN HE HAD EXPECTED. A CHLORINE FULL-FACE RESPIRATOR, LOCATED IN AN ADJACENT ROOM, WAS NOT USED. THE CHLORINE MONITOR IN THE CHLORINATOR ROOM EVENTUALLY FUNCTIONED BY TURNING A VENTILATION FAN ON. HOWEVER, THE AIR EXCHANGE RATE WAS NOT SUFFICIENT TO PREVENT THE BUILD UP OF CHLORINE GAS.