In which I find a weird PDF from the past
“Feasibility Study of Mining Coal in an Oxygen Free Atmosphere; A Demonstration of a New Mining Technique to Prevent the Formation of Mine Acid in an Active Deep Mine: Phase I”
The miner in the proposed process must work in an atmosphere that will have less than 0.1% oxygen and will be at 100% relative humidity. The life support system thus must not only supply breathing oxygen but must remove carbon dioxide all without contributing significantly to the oxygen content in the mine.
The idea was to avoid acid mine drainage by excluding the oxygen that oxidizes the pyrites to produce the sulfates by simple mining in inert gas with the miners wearing life support suits. This has real “guys will write a long proposal for coal mining in inert atmospheres before going to therapy” energy. 1970 was a weird time in environmentalism!