Maintenance personnel, responding to a dust emission report at coal mill #2 dust collector, found pressure relief panels (2 of 4) were open. Believing that an over pressure event occurred, MSHA was notified @ 2:25 AM. At 5:00 AM, MSHA was again notified of a fire that had begun @ 5:00 AM. This fire was quickly extinguished prior to 30 minutes.