The only survivor of a US mine disaster that killed 12 men in January says vital breathing equipment did not work.
Mr McCloy described the men's desperate struggle to escape
Randal McCloy said the four of the air packs issued to the men at the Sago mine in West Virginia failed to operate and the ones that did had to be shared.
The charge was contained in a letter to the victims' families, published by the Associated Press news agency.
The US mine safety agency denied the claim, saying all the devices recovered from the site were in working order.
The Mine Safety and Health Administration (MSHA) said tests showed that "those that were activated would have functioned properly".
MSHA spokesman Dirk Fillpot added that the agency was looking into whether the miners were properly trained to use them.
The International Coal Group, which owns the Sago mine, said the air packs were "all within the manufacturer suggested life", and were checked every 90 days.
The devices - which Mr McCloy refers to as "rescuers" in his letter - are intended to give each trapped miner an hour's worth of oxygen while they try to find a pocket of air.
But he says at least four failed to work. "There were not enough rescuers to go around," he said.
The letter also describes the 13 men's desperate struggle for survival after they were trapped deep underground by a blast.
"We found a sledgehammer, and for a long time, we took turns pounding away," Mr McCloy wrote.
"We had to take off the rescuers in order to hammer as hard as we could. This effort caused us to breathe much harder."
The miners died of carbon monoxide poisoning
Finally, resigned to their fate, the men said a prayer, wrote farewell notes to loved ones and lost consciousness.
By the time rescue teams reached them after nearly two days, all except Mr McCloy, 27, had died of carbon monoxide poisoning.
He spent weeks after the accident in a coma, unable to describe what had happened.
In the letter, Mr McCloy also says that three weeks before the disaster he noticed that a gas leak had been plugged with glue normally used to secure bolts.
A spokesman for the International Coal Group (ICG) told the BBC News website that the firm had no comment on the allegation.
A lawyer for the families of nine of the victims said the revelations contained in the letter were "very upsetting".
The ICG said the initial blast may have been caused by lightning.
State and federal investigators are conducting an inquiry into the disaster.