Abstract: A PRODUCING OIL WELL NEEDED TO BE ACIDIFIED. THERE HAD BEEN NO PREVIOUS INDICATION OF HYDROGEN SULFIDE OR IRON SULFIDE IN THE WELL. APPROXIMATELY 10 BARRELS OF 7.5 PERCENT HYDROCHLORIC ACID SOLUTION WAS PUT INTO THE WELL. THE HYDROCHLORIC ACID APPARENTLY REACTED WITH THE IRON SULFIDE TO FORM HYDROGEN SULFIDE. A PRESSURE SLIGHTLY ABOVE ATMOSPHERIC WAS CREATED IN THE WELL AS THE ACID FELL TO THE BOTTOM. EMPLOYEE #1, THE TANK TRUCK DRIVER WHO HAD TRANSPORTED THE ACID TO THE LOCATION, WAS INSTRUCTED TO WAIT 30 MINUTES AND THEN PUT 10 BARRELS OF SALT WATER IN THE WELL. THIRTY MINUTES LATER, WHEN THE WELL HEAD CASING VALVE AND THE TANK TRUCK GATE VALVE WERE OPENED, HYDROGEN SULFIDE WAS RELEASED FROM THE WELL, THROUGH THE TANK TRUCK, AND OUT THE TANK TRUCK VENT. EMPLOYEE #1 WAS EXPOSED TO A FATAL CONCENTRATION OF HYDROGEN SULFIDE.