This is what is known as a 'rescue chamber' - click title to read Power Point

In the power point presentation, it goes on to explain a far better form of 'built in' unit that has dedicated 'AIR LOCK' capacity.  What is also explained are the sincere dangers of mining and the ever present issue of air quality.  The definitions by Massey of what is acceptable OXYGEN levels or 19.5% is below any health standard employed by hospitals for patients, which is 21%.  The people of the USA have opportunity to change their means of obtaining energy and living free of any dangers provided the people of these towns.  I don't consider 'living dangerously' glamorous.  I consider it foolish.