A report by West Virginia investigators into the cause of the blast that killed 12 miners at the Sago Mine in January was supposed to be released today, but that release has been delayed after victims' relatives expressed dissatisfaction with the reports findings, CNN reports:

Sources told CNN the families felt there was not enough information in the report and there were too many unanswered questions.

The Associated Press, which obtained an advance copy of the report, says it claims that the methane gas explosion was nearly five times more powerful than the mine's underground seals were able to withstand:

The explosion was in an abandoned section of the mine that had been sealed less than a month earlier. The seals were designed by federal standards to withstand forces of 20 pounds per square inch, but state investigators found 10 seals were blown apart by forces at least 95 pounds per square inch.

The report claims that lightning sparked the explosion, but how electricity from the lightning entered the sealed area remains under investigation, the AP says. Six months after the disaster, the federal Mine Safety and Health Administration ordered that all seals must withstand 50 psi -- still less than the force of the Sago blast.

The report also found problems with the emergency air packs miners carry with them, saying the packs "did not perform in the manner expected," according to the AP.

The explosion occurred early on Jan. 2, trapping 13 miners who had gone underground to resume production at the International Coal Group-owned mine following the holiday. Only one miner survived. Another was killed in the initial blast, and the others died of carbon monoxide poisoning while awaiting rescue for more than 40 hours. It was the worst mining disaster in the U.S. since a 2001 disaster in Alabama that killed 13 people.

Earlier this month, the Mine Safety Technology and Training Commission -- which was formed in response to the Sago incident -- released a report in which it called on coal companies to adopt a culture of prevention.