My biggest problem with large tips in underground coal mines is you are about miles from the gas. Transportation isn't easy. Plus once you are at the end of the track you cant just drive up to wear you need your torches. You carry everything!A #6 would sure draw down the oxygen fast!!
Its not as simple as walking out behind the shop and grabbing a bottle. It may take hours or even the next shift before you see another bottle.
When guys are learning I always make them carry their own bottles. That way they learn quickly to conserve their supply. After carrying a bottle on your shoulder for a 1/4" mile you don't want to carry another....