Date of incident: June 2019
Notice of incident number: 2019177910004
Employers: Oil or gas production company; oil or gas field servicing companies (2)

Incident summary:
At a wellsite, two workers who operated a vacuum truck were vacuuming and cleaning fluids, sludge, and sediment from a low-pressure separator vessel (an LPS). Other workers opened two hatches on the LPS, and the two workers inserted their vacuum hose into a debris catch opening on it. Suddenly an explosion occurred inside the LPS, resulting in a flash fire. One of the two workers was thrown against an adjoining vessel by the force of the explosion. Both workers sustained serious injuries.

Investigation conclusions

Cause

• Electrostatic discharge ignited flammable atmosphere and caused explosion. While the workers were cleaning the LPS, an electrostatic discharge likely occurred within it, igniting flammable vapours and causing rapid combustion of flammable gases. The resulting explosion caused flames to exit the LPS’s inspection hatches, engulfing the immediate area where three workers were standing. The explosion also threw two of those workers away from the LPS.

Contributing factors

• Ineffective grounding and bonding. Post-incident testing confirmed that the vacuum system as a whole was not effectively grounded and bonded, as required to prevent the buildup of an electrostatic charge. Specifically, the vacuum hoses attached to the vacuum truck and inserted into the LPS were not effectively bonded to either the vacuum truck or the LPS.
• Inadequate inspection and maintenance of hoses. Firm A, a contracted field servicing company that employed the two workers who were injured, failed to ensure that vacuum hoses were regularly inspected and maintained to identify deficiencies or unsafe conditions. This allowed deficiencies to develop within the hoses’ electrical bonding wiring and create electrostatic discharge, a source of ignition.
• Inadequately identified and assessed hazards. Firm B, the oil and gas production company that was the prime contractor at the site, employed two on-site representatives, one of whom was in charge of activities at the worksite at the time of the incident. These representatives of Firm B had sufficient information pertaining to the contents of the vessels and the hazards associated with them. Firm B had the ability and resources on site to conduct thorough hazard assessments. To the extent that those workers did carry out hazard assessments before the vessel cleaning work started, the assessments were inadequate in relation to the rigout and cleaning activities involving the LPS and the use of vacuum trucks to transfer flammable fluids and materials. They did not take into account the need for LEL (lower explosive limit) monitoring, control of ignition sources around flammable substances, or verification of the grounding and bonding system. Firm B also failed to provide the contractors’ workers with safety data sheets to aid those workers in developing their own hazard assessments. The hazard assessments prepared by Firm A’s workers and those prepared by workers employed by a second field servicing company, Firm C, lacked sufficient information regarding acceptable explosive limits for flammable and explosive hydrocarbon vapours, proper control measures such as adequate grounding and bonding, and the use of conductive hoses and attachments.
• Failure to adhere to policies and procedures. Firm B has multiple standard operating procedures detailing requirements for identifying hazards, communicating them to workers, and eliminating or controlling them. Firm B failed to provide the relevant procedures to contractors. It also failed to confirm that contractors’ workers were trained to follow those procedures and failed to ensure the requirements of the procedures were enforced. Firm C also failed to ensure that its safe work procedures were implemented and adhered to. For example, neither firm verified the effectiveness of the grounding and bonding system or stopped the work process when it was identified that the concentration of toxic gases in the atmosphere was elevated above 20% of LEL, creating a flammable and explosive atmosphere inside the vessel. Firm A likewise failed to ensure that its safe work procedures were implemented and adhered to.
• Ineffective supervision. Workers of Firm C and Firm A did not adequately identify hazards at the site specific to the work process of cleaning the LPS, follow established safe operating procedures for work with flammable and combustible substances, or verify compliance with the requirement to maintain flammable gas or vapour concentrations below 20% of LEL.
• Ineffective information, instruction, and training. Workers of Firm C and Firm A had not received proper information, instruction, or training on how to ensure that effective bonding and grounding was achieved with the selected equipment. Nor had Firm B’s representative who was on site at the time of the incident. The lack of training resulted in failure to ensure that the equipment selected and used was adequate for the work activity and that the entire hydrocarbon-based fluid transfer system was effectively grounded and bonded.
• Inadequate oversight and coordination. As owner and prime contractor at the site, Firm B failed to coordinate the activities of multiple employers’ workers on site with respect to occupational health and safety. Further, it failed to do everything reasonably practicable to maintain a system to ensure compliance with the Workers Compensation Act and the Occupational Health and Safety Regulation. While contractors performed overlapping activities, Firm B failed to ensure those processes were completed so as to eliminate or minimize the unique hazards and associated risks faced by each individual contractor’s workers. For example, Firm B could have ensured that the LPS was purged or adequately ventilated before the Firm A’s workers began cleaning it. Firm B also failed to ensure that control measures required for the work tasks, namely, effective grounding and bonding of the vacuum system, were implemented prior to Firm A’s and Firm C’s workers performing the tasks. Firm B should have coordinated the work activities in a manner that reduced the risk to workers of exposure to unsafe environments. For example, Firm B could have established a system or process that ensured that the hazards associated with the work tasks were assessed and that control measures, such as maintaining LEL levels below 20% during the work activities, were implemented.

Request the full report