A South African inquest found preliminary evidence that five people, including unit operators and a shift team leader, were "negligent" and caused a deadly explosion at Astron Energy's Cape Town refinery that killed two employees three years ago.

According to findings by magistrate Ingrid Arntsen, dated June 14 but only released on Thursday, the incident occurred after gas valves were not properly closed, allowing gas to enter a furnace during start-up procedures following major maintenance.

Standard safety procedures required that all pilot and fuel gas face valves are closed prior to lighting of the furnace, with the incident immediately shuttering operations at the 100 000 bl/d refinery majority-owned by Glencore.

"All witnesses who testified as to the valves agreed that if the face valves were closed as required that the explosion would not have taken place," said the magistrate in findings seen by Reuters.

One of the operators was never traced and apparently went to work in the Middle East, while two others exercised their right to remain silent during the inquest, the document showed. The fourth operator on duty on July 2, 2020 attended the inquest but did not provide any statements.

"The unit operators were negligent in failing to close the face valves as required ... and that negligence is causally linked to the explosion that killed the two deceased," said the magistrate.

The shift leader, who lit the furnace that caused the explosion, was also found negligent because he did not wait for a back-up colleague before continuing, in violation of procedure.

The magistrate, however, found that Astron Energy had "all in all" complied with its duty in terms of the occupational health and safety laws.

The company, which resumed operations earlier this year after being shut down for repairs, said in a statement that it expresses its condolences to the families of the deceased employees and that it has "carefully considered" the findings.

"Astron Energy is of the view that it would be inappropriate to comment on the outcome of the inquest as all statutory and related processes have not been completed," spokesperson Suzanne Pullinger said.

The National Prosecuting Authority (NPA) said the matter has not yet been referred to their office.

"Once the full record is available, it will be sent to the director of public prosecutions for a decision regarding prosecution," an NPA spokesperson said.