Officials at Syncrude said a naphtha leak is to blame for Tuesday’s fire that led to thousands of workers being evacuated from the site.

The fire at the Mildred Lake Upgrader facility started at about 1:50 p.m. Tuesday.

Syncrude crews were quickly on scene, with RCMP and the local fire department also responding – workers on the site were evacuated.

“We take the safety of our people at the site very seriously so there’s protocols in place to ensure that the areas are vacated when something like this happens,” Syncrude spokesperson Will Gibson said in a phone interview.

On Wednesday, most of the 4,600 Syncrude staff were back on the job, except for those working near the line, which was leaking an oil called naphtha.

“It’s highly flammable and it was ignited,” Gibson said.

One person was taken to hospital as a result, rushed to hospital in Fort McMurray before being taken to Edmonton. The individual suffered serious injuries, but at last word was in stable condition.

“My thoughts are with the worker who was injured, I’m very glad that he was in stable condition,” Labour Minister Christina Gray said. “I know this must be terrible for him, the families and all the workers who are impacted.”

The facility is located about 35 kilometres north of Fort McMurray on Highway 63. Staff said the fire took place in the plant’s upgrading complex, where oil is processed and blended before being shipped away.

Billowing smoke prompted an air quality warning, which remained in effect Wednesday.

The area where the explosion happened remained restricted Wednesday, while crews assess the scope of the damage.

The fire was deemed under control late Tuesday afternoon, but continued to burn Wednesday, as officials said the fire was being allowed to burn itself out.

Once the area is safe to access Occupational Health and Safety will begin their investigation.

With files from Shanelle Kaul