DandyDon,
The actual calculation can be carried out, but here is why I think that the bends is not a likely outcome without doing the math:
1. Elevation dive tables are available in 2000 foot increments. If you are within 1000 feet of sea level, you assume sea level pressure. The miners are less than 2000 feet below the surface, are they not? I dive 4000 feet regularly. This is analogous to treating a 90 ft dive as 110 ft wrt DCS. Not a huge hit;
2. The air in the mine is very hot (28 C or thereabout?) Hot air is less dense than cold air. The air cools up the shaft as you rise, but the net effect of the decreased air density in the mine makes the pressure at the bottom of the shaft less than it would be if the air column had the same uniform surface temperature. For example, air at 30C (mine bottom) is about 5% less dense than air at 15C (a surface estimate). Again, not a huge difference, but it is a plus for the miners.
Have you seen the (small) size of that cage??? I dive in LOTS of thermal protection, but THAT would press the limits of my self-control.
