John Roberts, 39, suffered deep burns to his face, arms, hands and chest but managed to leave the mill, climb a high wall and drive to his girlfriend's house several miles away.

His girlfriend, Nina Hurley, said that Mr Roberts arrived screaming at her house around 5am.

"I could hear a strange screaming noise," she said in a statement: "He screamed 'Help me'. He came in and sat down. His breathing was not good, he was going into shock, he could barely speak. His T-shirt had been burnt off and his face was all blackened. His eyelashes and hair were all burnt."

The hearing in Leeds was told that Mr Roberts – known to many as Bod – was taken to hospital but died on August 14 last year in the burns unit at Pinderfields Hospital, Wakefield, 10 days after the accident.

He had suffered deep burns to 37 per cent of his body and died from multiple organ failure, sepsis and burns.

The inquest heard that Mr Roberts, who described himself as a self-employed scrap metal dealer, entered Park Mill in South Street, Morley, by scaling a wall and removing padlocks.

He forcibly entered a locked room containing a transformer, ignoring a warning notice about 11,000 volts and the tell-tale buzzing of the transformer.

Mr Roberts, of Winrose Avenue, Belle Isle, Leeds, was in the process of removing copper bars from a switch box when there was a huge explosion which possibly vaporised the tool he was using.

Det Sgt Paul Smith, who investigated the incident, said there was evidence that electrical equipment in the mill had been systematically stripped of copper.

Det Sgt Smith said the temperature from the explosion would have been "severe" and would have been similar to having a blow torch held against the skin.

The owner of the mill, David Green, said in a statement that the mill was securely locked because he was well aware that it would have been attractive to criminals and children.

He had not been aware of a break-in until the police contacted him about the death of Mr Roberts, he said in the statement.

Gill Douthwaite, a friend of Mr Roberts, told the hearing that she used to collect scrap metal with him and the pair had visited the disused mill two days before the accident.

She described how they had climbed over a 6ft wall and prised a padlock off to get into the mill. A second door was also forced open to get to an electrical box.

The pair then left the premises and she never saw Mr Roberts again.

"I texted Bod but there was no reply. I was told he had charged himself on cable. I felt responsible as I had shown Bod the mill in Morley."

Deputy assistant coroner Melanie Williamson recorded that Mr Roberts died as a result of misadventure.

She added: "I am in absolute amazement at how John managed to leave the transformer room, get over the wall and drive to Nina's house. He must have been in immense pain. He must have had both incredible physical but also mental strength."