Hi there Mr. Z!,

I think there's one aspect of this that hasn't yet been touched on, which may explain why two 100s got emptied on the return; he had been digging (that's partly why "exploration is a four letter word"). He was a mile in, and his own silt cloud meant that he would have had next to no visibility on the way out - OK-ed on the line the whole way. Remember that silt cloud was bad enough at the entrance to have Ginnie's management worried about danger to other cavedivers; near the face where he was working it must have been horrendous. Absolute brownout. Zilch. He had major restrictions to negotiate in the dark. Small wonder his air supply didn't last.
One lesson is to allow lots of extra time for an exit if you intend to dig, above all if digging in a spring rather than a siphon. Another is that a bailout breather might have saved his life by allowing him to eke out those big 100s in SCR mode.

Soberly,

Charles.