Date of incident: November 2018
Notice of incident number: 2018177910008
Employers: Oil and natural gas producer (prime contractor); water treatment company; oilfield testing service provider

Incident summary
Workers were conducting well flowback activities when a low-pressure flowline (a metal pipe) violently ruptured and pieces of equipment were thrown across the worksite. A piece of the flowline system struck and ruptured a large plastic tote containing approximately 1130 L of hydrogen peroxide (H₂O₂) 50% (a 50% solution of H₂O₂ in water). The H₂O₂ splashed onto a worker in the immediate area, and the worker sustained serious injuries.

Investigation conclusions

Cause

• Exothermic reaction caused by decomposition of hydrogen peroxide. The wells contain hydrogen sulfide, a poisonous gas, in concentrations of 6400 parts per million (ppm). Hydrogen sulfide is lethal at concentrations of 700 ppm. Because of the inherent risks of high levels of hydrogen sulfide, H₂O₂ was being added to neutralize the hydrogen sulfide. The investigation found that it is likely that when the operator of the water treatment equipment increased the flow rate of the chemical injection metering pump, the increased flow of H₂O₂ came into contact with hydrocarbon-based fluids (condensate) that contained organic matter. This action started a rapid decomposition of the H₂O₂, which caused an explosion that ruptured the flowline.

Contributing factors

• Inadequately identified and assessed hazards. The hazard assessments prepared by the prime contractor at the site, the operator’s employer (the water treatment company), and the oilfield testing company did not address any of the hazards related to the use, handling, or storage of H₂O₂. Workers lacked sufficient information regarding limits for the mix of hydrocarbon-based fluids and H₂O₂ 50%. If the correct information had been used in the hazard assessment, workers, including the operator, would potentially have been able to make informed decisions on flow rates, injection rates, and mitigating factors.
• Lack of safe work procedures. The water treatment company failed to develop and implement a procedure for the safe use and handling of H₂O₂. The prime contractor failed to ensure that safe work procedures were developed and implemented by its workers and its contractors for a dangerous work task that involved mixing chemicals. With effective safe work procedures, the operator would have been able to use the correct procedures to deal with any unbalanced conditions that arose.
• Failure to effectively coordinate work activities. The prime contractor failed to ensure that the activities of workers from multiple employers at the worksite were effectively coordinated with respect to occupational health and safety. Effective coordination between the prime contractor and the workers on site would have ensured that the workers implemented effective hazard control measures for the work tasks. While contractors performed overlapping activities, the prime contractor failed to ensure that those processes were completed in a way that eliminated or minimized each individual contractor’s unique hazards and associated risks.
• Lack of information, instruction, training, and supervision. The operator’s employer failed to provide the operator with adequate information, instruction, and training. The employer failed to ensure that the operator was adequately trained in the safe operation of the chemical injection metering pump used to transfer a highly volatile chemical. The prime contractor failed to ensure that safe work procedures and exposure control plans were provided and adhered to for the work tasks, including safe work procedures for mixing H₂O₂ with hydrocarbon-based fluids and an exposure control plan for H₂O₂. Neither the employer nor the prime contractor provided adequate supervision for workers who were using and handling chemicals.

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