MORGANTOWN, W.Va. -- Gov. Earl Ray Tomblin placed a wreath with 29 white roses at the West Virginia Coal Miner statue outside the state Capitol in Charleston on Thursday as people across the state paused for a moment of silence to mark the second anniversary of the Upper Big Branch mine disaster. "Tomorrow, we can take up our conversations about how to improve mine safety and keep another disaster like this from happening ever again," United Mine Workers of America President Cecil Roberts said in a statement. "As important as that is, today is a day for us to pause and think about the families." The powerful April 5, 2010, explosion at the former Massey Energy mine near Montcoal was fueled by methane and coal dust, traveling miles of underground corners and killing men instantly. It was the worst U.S. mine disaster in four decades. "Our hearts broke when we heard that they were gone," said U.S. Sen. Jay Rockefeller, "and it's something no West Virginian will ever forget." The disaster has since led to a $210 million agreement between the mine's new owner, Virginia-based Alpha Natural Resources, and the U.S. Department of Justice. The agreement settles past violations and protects the company from criminal prosecution. Individuals, however, remain on the hook. Former mine superintendent Gary May recently pleaded guilty to a charge of defrauding the federal government for his actions at the mine and is cooperating with investigators in their continuing criminal probe. May is the highest-ranking company official charged in connection with the blast so far and could get up to five years in prison when sentenced in August. Former security chief Hughie Elbert Stover, meanwhile, is appealing his three-year sentence for lying to investigators and ordering the destruction of documents after the blast. And on Wednesday and Thursday, two of the dead miners' families filed civil lawsuits against both former Massey executives and an independent contractor that was cited for violations that contributed to the blast. U.S. Labor Secretary Hilda Solis called the explosion "the single most heartbreaking day of my tenure" and touted the many changes that the federal Mine Safety and Health Administration has since made "to counteract the type of misdeeds that were so prevalent at Upper Big Branch." Several investigations have determined that Massey systematically covered up problems at Upper Big Branch through an elaborate scheme that included sanitized safety inspection books and an advance-warning system that let miners underground know inspectors were onsite. "If every mine operator meets its legal obligation to ensure the safety and health of its workers," Solis said, "we can prevent another tragedy like the one at Upper Big Branch from ever happening again." U.S. Rep. Nick Rahall said he hopes the now-infamous date will ultimately mark "a turning point in our national commitment to miners." Rahall, D-W.Va., has been pressing congressional colleagues to act on long-stalled legislation that would give stronger protections to coal miners who blow the whistle on dangerous conditions, give MSHA federal subpoena power and impose stiffer criminal penalties that would be a meaningful deterrent. "I remain committed to working to pass legislation that will prevent bad-actor operators -- a small minority of our coal companies -- from calculatingly breaking the law and putting their own miners in danger for the sake of profit," Rahall said. Sen. Joe Manchin, who was governor at the time, said he thinks about the tragedy every day "and the fact that it could have been prevented." He vowed to fight every day to make the safety of miners a priority. "All the miners across the country who kiss their families goodbye before leaving for a shift should know that they will return home again safely," he said. An MSHA 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. But a team led by the National Institute for Occupational Safety and Health recently concluded that timely enforcement of existing regulations "would have lessened the chances of -- and possibly could have prevented" the explosion. Although MSHA inspectors wrote 684 violations in the 18 months prior to the blast, the agency 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. MSHA director Joe Main said last week those cases have since been turned over to federal prosecutors. Alpha marked the anniversary by announcing late Wednesday that the mine will be sealed with concrete. The company said it will seal the portals -- large tunnels miners use to get underground -- at the mine. Boreholes will be plugged and shafts that house the huge industrial fans meant to sweep bad air out of the mine will be capped to prevent any access. The job should be finished by summer, the company said.