The owners of a US mine where 12 men died in an accident in January have dismissed allegations that the miners' emergency oxygen bags were faulty.
Mr McCloy described the men's desperate struggle to escape
The sole survivor of the accident at Sago in West Virginia, Randal McCloy, said that at least four of the air packs had malfunctioned.
But the International Coal Group said the packs had been checked regularly.
The firm pointed to tests carried out by the US mine safety authority, which suggested the devices were working.
The Mine Safety and Health Administration (MSHA), which analysed air packs recovered after the accident, said "those that were activated would have functioned properly".
An MSHA spokesman added that the agency was looking into whether the miners had been properly trained to use them.
The International Coal Group, for its part, said the air packs were "all within the manufacturer suggested life", and were checked every 90 days.
Mr McCloy's allegations were contained in a letter sent to the families of his late colleagues.
He said at least four of the devices - which Mr McCloy refers to as "rescuers" - failed to work and those that did had to be shared.
"There were not enough rescuers to go around," he said.
The letter 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.
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 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 International Coal Group said the initial blast may have been caused by lightning.
State and federal investigators are conducting an inquiry into the disaster.