The phrase Draegerman originated with Alexander Draeger (1870-1928), aka Drager. He was a German scientist and inventor who created the first combination gas mask and air supply for rescue teams in the late 20's. Hence mine Search and Rescue workers were referred to as Dragermen or Dragerwomen; a tradition that continues today in mining areas both in the EU and US.
The movie is based on an actual cave-in in 1936 at the Moose River Gold Mine in Nova Scotia, Canada