VICKI SMITHMORGANTOWN, W.Va. (AP) â¿¿ While Republican lawmakers questioned the head of the federal Mine Safety and Health Administration over inspection failures at West Virginia's Upper Big Branch mine, U.S. Rep. Nick Rahall and other House Democrats demanded action Tuesday on stalled legislation to give the agency more power. The Capitol Hill hearing was the third time MSHA chief Joe Main has testified before Congress about the 2010 explosion that killed 29 Massey Energy coal miners. It was the worst U.S. mining disaster in 40 years. A recent internal review concluded that federal inspectors either missed problems or failed to examine areas where they existed in the 18 months before the blast but found no evidence those failures caused it. Last week, though, a team led by the National Institute for Occupational Safety and Health issued a report concluding that timely enforcement of existing regulations "would have lessened the chances of â¿¿ and possibly could have prevented" the explosion. Rep. John Kline, R-Minn., and chairman of the House Committee on Education and the Workforce, joined his GOP colleagues in repeatedly pointing to the reports as a sign of chronic failures. Kline said he found it "difficult, almost impossible" to imagine how inspectors could have failed to notice accumulations of explosive coal dust and why certain administrative tools "were either poorly used or never implemented." Although inspectors wrote 684 violations in the 18 months prior to the blast, the report said they failed to act on eight that could have been deemed "flagrant," the most serious designation. They also failed to conduct special investigations on at least six occasions to determine whether managers knowingly violated safety standards. Main said those cases have since been turned over to federal prosecutors. Main, who started months before the disaster, has since launched a stepped-up inspection program for mines with a history of problems and other programs to make U.S. operations safer. He insisted he's "on a path to really fix MSHA."