In 1942, Office of War Information photographer John Collier visited the Montour No. 4 Mine of the Pittsburgh Coal Company in Washington County, Pennsylvania.
Montour No. 4 was a mine for bituminous coal, one of the most volatile forms, requiring the miners to vigilantly monitor for the presence of flammable gases.
Collier followed the miners as they moved underground through the near-horizontal drift mine, laying track for machinery, drilling and blasting with dynamite, all the while maintaining caution for possible collapses or explosions.