Burning hydraulic fuel exploded on a scrap-metal worker in Richmond yesterday, burning him for 20 seconds before co-workers could put out the flames.

"He was screaming. I've never heard him scream like that before. From the foot up, he was on fire ... three of us were sort of jumping on him, rolling him around but it wouldn't go out," the man's foreman, Levi Newport, said.

The accident happened at General Metal Recyclers, by Three Brothers Corner, where three months ago a pile of cars caught fire, requiring an extensive firefighting effort as black smoke billowed across State Highway 6.

Yesterday's accident happened about 11.30am. Mr Newport said he was working on a forklift when he heard Craig Lawson scream and saw him come running towards him ablaze. Despite the best efforts of workers, the fire continued for "probably a good 20 to 30 seconds".

"I ran inside, called the ambulance, and when I went back he was still on fire. Then we got it out and the tank caught back on fire, so we had to run back and get the extinguisher. It definitely got out of hand pretty quick," he said.

Richmond Volunteer Fire Brigade senior station officer Blair Hall said it appeared the man was gas-cutting a tank that contained hydraulic fluid.

"It appears the fumes in the tank have exploded and covered him in hydraulic oil, which has been burning and his workmates have basically put him out. Gas-cutting any sort of container is pretty dangerous," he said.

Mr Newport said he was not sure if the tank just exploded or Mr Lawson cut it.

St John rural support officer Lindsay McCaw said the man was treated for burns on his legs and was lucky not to come away with worse injuries.

"He was a little bit lucky that his burns were confined to his lower leg, not on the greater part of his body. He has moderate to severe burns on one leg, about 5 per cent of his body area. Burns like that tend to be quite painful because it does tickle the nerve endings," he said.

Mr Lawson said from the back of the ambulance yesterday he was in a lot of pain and still in shock. "Yeah, it was just boom, real quick."

Department of Labour officials said they were investigating the accident, but had no further comment.