A roofer was left dangling nearly four storeys in the air. (CBC)

A Saint John worker who slipped from a roof avoided serious injury thanks to his safety harness.

The roofer was left dangling nearly four storeys above a paved driveway until firefighters could help him down.

Fellow worker Scott Vautor said some rotten wood along the edge of the roof of the Douglas Avenue building in Saint John likely caused the accident.

"He basically went down a little too far and there was rotten stuff — as you can see all down here over, on the pavement here — and he just fell. Thank God he had this on right here," Vautor said, pointing to his safety harness.

Rescuers estimated the distance at about 12 metres.

Firefighters called to the scene were able to slowly lower the man, 50, on to a ladder. He was then was able to climb down to the ground on his own.

The worker, who suffered minor injuries including bruising, was taken to hospital as a precaution.

"It is important to always observe the proper safety protocols and what not, and it appears that they have in this case," Saint John District Fire Chief Eric Garland said. "And that's probably what's made this gentleman's descent to the ground a little bit easier."

Vautour said the incident taught him a lesson about safety

"I've thought about not wearing it [the safety harness], but I will now," he said.

Worksafe New Brunswick is investigating the accident.