Date of incident: October 2013
Notice of incident number: 2013170090251
Employer: Service provider to the oil and gas industry

Incident summary

At the site of an inactive gas well, two workers were flowing the high-pressure gas from the well to determine production potential. They were inside an operator's shack when a pipe ruptured, and the escaping flammable gas exploded in a fireball. Although the two workers were wearing fire-retardant clothing, they suffered burns. The smaller piping downstream from a pressure relief valve (PRV) was one of the factors that caused the piping system to fail.

Investigation conclusions

Cause

• Piping ruptured after PRV opened, resulting in fireball: When the PRV inside the operator's shack opened, the sudden force of the escaping gas caused the piping to rupture. The pipe struck the roof of the shack, lifting it off and exposing live wires. At the same time, the flammable gas exploded in a fireball.

Underlying factors

• Policies, procedures, and standard industry practices not followed: The two workers, who had direct control of the gas-testing equipment, operated the equipment close to the maximum operating pressure (MOP) until the PRV opened. Standard industry practice is to stay below 80 percent of the MOP.
• PRV piping not connected as required: When the PRV opened, the downstream piping, which was not connected to the flare stack, failed due to excessive movement. As a result, the flammable gas released into the operator's shack.
• Diameter of the piping downstream of the PRV reduced: The outlet piping downstream of the PRV was reduced from 4 inches to 3 inches. This resulted in increased pressure from the escaping gas on the smaller-diameter piping.
• Pipe failure likely caused the gas to ignite: When the piping downstream of the PRV failed, flammable gas released from the piping into the operator's shack. The ruptured pipe damaged the shack, exposed live wires, and created metal-on-metal contact. The gas was most likely ignited by one or more of these sources.

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