The illegal use of a cutting torch ignited an underground methane gas explosion that killed five coal miners last year, and the mine operator was fined $336,000 for the violations, federal investigators said late Thursday.

The Mine Safety and Health Administration met with the miners’ family members to discuss their investigation of the deadly blast before their report was released to the public.

Kentucky Darby Mine No. 1 violated six safety and health laws, including the torch and flawed construction of the safety barrier that caused the blast at Darby Mine No. 1, according to the report.