- Heat exhaustion. At depths greater than 1000 feet the air temperature could be 120º or more.
- Falls. Sometimes when men were brought up into the cooler air they would faint and fall out of elevators/down shafts. Their bodies were often shredded by banging into timbers and cables on the way down, such that grappling hooks were kept near the sump-pit at the bottom, to fish flesh and bone out of the hot water.
- And by the way you didn't want to fall in that sump pit, even from a short drop, because it was a good deal hotter than a hot tub. One guy at the Comstock fell in to his waist and all the skin sloughed off his legs. He died.
- Cave-ins were a constant danger. Although the walls and shafts were shored up with timbers, mineral-rich earth is notoriously unstable and tends to shift. And if your foreman is an asshole he may have cut corners on the shoring-up.
- Then there's the ever-present threat of fire, when all you have for lighting is open flame. Amid the flammable coal and gasses underground. And if your fire abruptly goes out you're looking at asphyxiation from a buildup of non-flammable, non-breathable gasses.