The union that represents most of the employees at Suncor Energy says it has lost faith in the company’s safety systems following the fourth death of a worker this year.

On Monday, a 37-year-old man employed by North American Construction died after a part fell on his head while he was working on a dozer at Suncor's Steepbank Millenium MIne near Fort McMurray.

Roland Lefort, president of Unifor Local 707-A, the union that represents all but the most recent worker to die, says he is disappointed and angry over the man’s death.

"Why?” Lefort asked. “Questioning again what are the things that we could have done to make sure that this one didn't happen."

Last month, Suncor instrumentation technician Lorna Weafer, 36, was killed in an attack by a black bear.

In April, 27-year-old Shane Daye, also an instrument technician, died in hospital after he was severely injured on the job.

Jerry Cooper, a 40-year-old Suncor tailings operator originally from Newfoundland, was found dead in a large pool of sand and water at the Suncor operation last January.

The incidents that caused the workers' deaths all took place at the same Suncor site.

Unifor opened its own investigation after Daye’s death. Occupational Health and Safety is also investigating.

However, OHS spokesman Brookes Merritt says there is little reason to believe the four fatalities are linked.

"They are disparate in nature,” he said. “We have a drowning, we have an electrocution, we have a bear attack, and then we have this most recent fatality.”

But Lefort says his members have lost faith in the company’s safety systems. He is telling workers to look out for themselves.

"Because I don't have the answers,” he said. “I'd much rather that my members take care of each other right now. Until we find out what the hell is going on.”

A Suncor spokesperson told CBC News that the company had already set up a task force to investigate safety at the plant prior to the recent fatality.