An explosion ripped through Willow Grove Mine No. 10 on March 16, 1940, killing seventy-two men, traumatizing their families and the community, and contributing to increased mining regulation. After the blast, people rushed to help and more than one hundred workers were rescued from the tunnels in the following hours. Federal and state officials assisted in rescue and recovery, expedited financial aid to the bereaved, and carried out investigations. Although the Hanna Coal Company promoted Willow Grove as a modern mine with mechanized equipment and safety training, later research found that black powder used in firing a shot to open a coal seam ignited accumulated gas and coal dust in the tunnels, causing the massive explosion. Two months later, experts testified about Willow Grove before a Congressional subcommittee, and by 1941 the Mine Inspection Act had been passed to let federal inspectors enter mines and make safety recommendations.
