Two workers lost their lives when the supplied breathing air cylinders they were breathing from contained low levels of oxygen. The two workers were working on top of a scaffold, sandblasting the interior of a boiler. A third worker was outside the entry to the boiler to make sure the breathing lines did not become tangled and served as a communications link.
After an unknown amount of time passed, the third worker discovered that the two coworkers had collapsed and were lying on the bottom of the tank. Emergency personnel removed the workers from the tank, but resuscitation efforts were unsuccessful. Further investigation revealed the blended breathing air supply involved three separate 12-packs of cylinders. Each cylinder was analyzed and found to have varying oxygen concentration levels between 5% and 10%. See link below for full incident report.
