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Worker burned by flash fire when liquid hazardous waste was unloaded

Date of incident: September 2013
Notice of incident number: 2013170090220
Employer: Oil and gas field service company

Incident summary

Workers were unloading liquid hazardous waste from a pup tank into an open hopper at a hazardous waste processing facility. The pup tank was connected to a vacuum truck, and the truck's engine was running. Flammable gas and vapour was released into the atmosphere. The flammable gas and vapour ignited, resulting in a flash fire. One worker sustained serious burn injuries.

Investigation conclusions

Cause

  • Release of flammable gas or vapour in the presence of a running truck engine: The liquid hazardous waste contained in the pup tank was ready to be discharged into an open hopper. When the discharge valve was opened, liquid came out under pressure, resulting in an uncontrolled release of flammable gas or vapour into the air, and the development of a flammable atmosphere. The truck engine was the ignition source.

Underlying factors

  • Inadequate hazard assessment: The hazardous waste facility conducted a site-wide hazard assessment several months before the incident. The assessment failed to identify a fire and explosion hazard associated with the release of airborne flammable gas and vapour during the offload of waste into the open hopper.
  • Inadequate design of open hopper: At the hazardous waste facility, operators routinely offload vacuum trucks into the open hopper. The open hopper was not designed to ensure that the airborne concentration of flammable gas or vapour could not exceed 20 percent of the lower explosive limit (LEL).
  • Failure to control ignition source: The truck engine was running to provide power to the truck's hydraulic system, which was needed to raise the pup tank. The discharge valve was opened, which allowed the hazardous waste to be released into the open hopper. As a result, airborne flammable and combustible vapours were able to enter the truck engine's air intake system and ignite.
  • Flammability hazard of the waste mixture was unknown: The degree of the flammability hazard for the product in the pup tank was unknown to the facility operator before he directed a worker to open the discharge valve. There were several reasons for the operator's lack of awareness. He was provided with inaccurate information regarding the contents of the tanks. He had no way to verify the contents in the tanks. He did not review the documentation truck ticket or manifest. He did not receive an MSDS or hazardous waste profile sheet from the company disposing of the hazardous waste.

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Publication Date: Sep 2013 Asset type: Incident Investigation Report Summary NI number: 2013170090220