Date of incident: December 2019
Notice of incident number: 2019178760030
Employer: Oil or gas field servicing companies (3); oil or gas production company

Incident summary
Workers at a natural gas wellsite were preparing to vacuum and clean fluids, sludge, and sediment from a low-pressure separator vessel (LPS) when an explosion occurred inside the vessel, resulting in a flash fire. One worker sustained serious injuries during the incident.

Investigation conclusions

Cause

Failure to control ignition sources. The investigation found that while the workers were cleaning the LPS, a pyrophoric reaction likely occurred within the vessel when oxygen was introduced into it, igniting flammable vapours and causing rapid combustion of flammable gases. The resulting explosion caused flames to exit the vessel’s inspection hatches, engulfing the immediate area where one worker was standing. The worker was thrown away from the vessel and sustained serious injuries.

Contributing factors

• Failure to adequately analyze risks of work activities. The risk assessment document prepared for the equipment supplier before the vessel cleaning work started did not identify the task of cleaning out the LPS. The document identified only that there was a fire and explosion hazard and did not identify any sources of ignition (other than smoking) or fuel sources such as the hydrocarbon vapours that may still be present after purging. The document referred to having met the obligations stipulated in a key industry guideline, but those obligations had not been met. The risk assessments prepared for the vacuum truck service provider before the vessel cleaning work started identified some hazards associated with the work, but also contained inaccuracies. The prime contractor failed to analyze the risks associated with cleaning the equipment supplier’s pressure vessels of materials from its own wells. The vessel cleaning operations involved hazards that are well-known in the industry. The prime contractor’s template for a site-specific fire and explosion hazard management plan identifies some of these hazards. However, the prime contractor did not ensure such a plan was completed, and allowed the work to commence without effective hazard control measures in place.
• Failure to react to safeguards. While the workers were cleaning the LPS, the personal gas monitors of two workers alarmed more than once for H₂S and LELs (lower explosive limits). When these alarms sounded, the workers routinely reset their monitors, quelling the alarms. As well, when the alarms sounded, they did not inform other workers or supervisors of these developing conditions. The safety supervisor was using a passive gas monitor to test the atmosphere in front of the inspection hatches as the hatches were opened, before the workers started cleaning activities at each hatch. If a pump-style monitor with a wand had been used, and the vacuum had been turned off, the safety supervisor might have been able to detect hazardous atmospheric conditions developing inside the vessel being cleaned. If the information regarding the explosive atmospheric conditions developing inside the vessels prior to the explosion and fire had been relayed to the prime contractor’s on-site representative, the vessel cleaning operations might have been stopped, a new risk assessment might have been conducted, and safe work procedures (SWPs) might have been put in place.
• Lack of information and instruction led to key health and safety failures. When the job scope changed from flowing the wells to cleaning the pressure vessels, employers on site failed to advise one another’s workers of information about the hazards of cleaning the vessels. Safety meetings that were held did not include all workers who were required to conduct the vessel cleaning and did not provide adequate information about the hazards present. If a safety meeting that included all workers involved in the task of cleaning vessels had been held prior to the vessel cleaning, all the workers would have been aware of each employer’s SWPs and of the hazards stemming from the task.
• Ineffective supervision. A number of supervisory failings on the incident day contributed to the incident. There was a failure to ensure that workers performing overlapping work activities attended safety meetings held by various contractors. As a result, workers were not made aware of the hazards posed to them by the work activities. Other failures included not ensuring that the prime contractor’s on-site representative was informed about the initial fire at the site; not ensuring that the equipment supplier’s SWPs were adhered to; and allowing work to continue when alarms sounded on two workers’ personal gas monitors.
• Inadequate oversight and coordination. The prime contractor failed to meet its responsibilities as owner and prime contractor at the incident site. It did not adequately coordinate the activities of multiple employers’ workers at the site. It did not do everything reasonably practicable to maintain a system that would ensure that work at the site complied with the Workers Compensation Act and the Occupational Health and Safety Regulation. Nor did it ensure that hazards associated with contractors’ activities were communicated to all workers involved. The prime contractor also did not ensure that its contractors were completing tasks according to each employer’s own SWPs. And, as mentioned, it did not adequately analyze the risks of work activities that posed a significant risk of injury to workers and ensure SWPs were implemented to address hazards associated with the activities.

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