NEW : The explosion was the mining industry 's worst disaster in 40 years . The West Virginia mine that exploded in April had a sudden influx of methane . It is not clear how much gas escaped, but it could have been enough to cause an explosive reaction and blast off into space. The release of methane was almost three times greater than normal .
NEW : The explosion was the mining industry 's worst disaster in 40 years . The West Virginia mine that exploded in April had a sudden influx of methane . It 's too soon to say whether the gas caused the explosion , investigators say . The release of methane was almost three times greater than normal .