On the day before the accident, Eric R. Willis, millwright second class, and Gary Passmore, were assigned to repair leaks in the freeze system at No. 4 caisson, Plant 1.  They worked at the assigned task for half the day; then Brent Black, millwright first class, replaced Passmore.  They finished that shift and on the following day worked on the repairs until 2 p.m.  The nitrogen pipelines were repaired, a welded plug was removed from the freeze jacket, a hole about 4 inches square was cut in the jacket, so mud could be washed out, and the cut out piece welded back in place.

Compressed air was then blown through the freeze system to make sure all the water was out.  Merlin Hamilton, maintenance foreman, was present when the freeze system was blown out with compressed air.  After telling Black and Willis to connect the nitrogen to the line and start the freezing process and assigning Willie Dodderer and Elmer Price to assist Black and Willis, he went to his office.

A rubber hose from a trailer containing liquid nitrogen was connected to the inlet line and the valve opened.  The flow was adjusted so a vapor was emitted from the exhaust line.  A positive method to tell when the underflow line was frozen was not provided, however, it was known from past experience that when the jacket was completely covered with frost, after approximately 4 hours of freezing, the nitrogen could be turned off and repairs completed.

The caisson was not ventilated and no instruments were available to monitor the air.  The freeze system had not been pressure-checked for leakage prior to being connected to the nitrogen source.  Dodderer and Price arrived at the caisson about 3 p.m., and at about the same time, Black left the area of the caisson.  When he did not return in a few minutes, Willis, Dodderer, and Price went to the main shop and their own shop for tools before returning to the No. 4 caisson.  Black was not in sight and after looking for him at the nearby control room, they decided to continue without him.  Dodderer climbed the ladder to the platform near the top of the caisson.  He looked down into the caisson and thought he saw someone in the bottom.  He immediately started down the ladder into the caisson, followed by Willis.

They yelled to Price outside the caisson to shut off the nitrogen and go for help because Black was down there.  On arriving at the bottom, Dodderer tried to lift Black and found his body frozen to the ground.  Willis then remembered that his foreman had told him that nitrogen "froze the oxygen" or something like that.  Price heard Willis yell at Dodderer, "get out of here, you won't be able to breathe."  About half way up the ladder, Willis looked down and thought he saw Dodderer start for the ladder.  He climbed out and went with Price, who had turned off the nitrogen valves and was leaving in the pickup.  They went to the main shop, reported the accident and went for the nurse.

When they returned to the caisson, less than 5 minutes had elapsed.  Joe Lanyon, granulating plant maintenance foreman, and Wilbert Kennedy, general plant maintenance foreman, were on the platform at the top of the caisson.

After calling for ropes and resuscitators, they cut the oxygen hose at the welding torch and adjusted the oxygen flow.  Lanyon placed the end of the oxygen hose between his teeth and with a rope tied around his chest, descended into the caisson.  About half way down, the hose came out of his mouth and he let it fall to the bottom.  He climbed back up the ladder because of a sensation that he was not getting any oxygen.  The oxygen hose was pulled up and Lanyon was given pure oxygen until he was breathing normally.  He then dropped the oxygen hose back to the bottom where it discharged oxygen into the atmosphere for approximately 3 to 5 minutes.  Lanyon then descended to the bottom to tie a rope on Dodderer and called for help, and Kennedy (without a lifeline) climbed down to help him.  They tied the rope around Dodderer and tried to pull him out by hand, but the rope slipped when he was raised just off the bottom.  After securing safety harnesses from nearby workmen, the two victims were hoisted to fresh air by a mobile crane, which had by then been positioned above the caisson.

Resuscitation attempts were unsuccessful.  Both victims were transported to the hospital in Boron, California where they were pronounced dead.