Summary

At a well stimulation site, an operator needed to release excess carbon dioxide (CO₂) from a mobile tanker unit, known as a queen. The queen was parked between two other queens, so the excess gas could not be released directly out to the side. To redirect the venting gas to the front of the queen, the CO₂ operator constructed a pipe assembly using available piping components. When the CO₂ operator opened the discharge valve to release the excess CO₂, the pressure of the venting gas unthreaded the pipe assembly and it spun counterclockwise. The pipe assembly struck the CO₂ operator, causing fatal injuries.

Conclusions

Findings as to causes

• A CO₂ operator released CO₂ gas from a queen by using a vent pipe assembly constructed of on-site components. When the pipe assembly unthreaded and turned counterclockwise, it struck the CO₂ operator, causing fatal injuries.
• Where the CO₂ gas hit the angled pipe assembly, the pressure of the gas caused the pipe assembly to spin off the threaded mount of the outlet.

Findings as to underlying factors

• Work procedures were inadequate in describing where to position the queens safely for releasing a gas into the atmosphere.
• There were no instructions to workers on where to stand when opening the discharge valve.
• Failure to provide for adequate supervision led to a situation where the workers were left to direct themselves and to improvise solutions to the problems they encountered.

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