The single worst workplace disaster in US history.
Men were sent in to a mine with either no or inadequate breathing equipment, and slowly suffocated after contacting silicosis.
One man living with his mother had to be carried to bed. "Mama I tell you I cannot get my breath" were some of the last words he'd speak.
Silicosis is no fucking joke. It can take years before you notice you have it, there's no reversing it, and you will not enjoy another moment of life once you do. It can take a long time to die and you will loathe every minute of it. That's if your exposure is limited.
If you're working around this shit all the time, or in the case of the Hawks Nest tunnel, your exposure is nearly constant, you'll die over a matter of weeks, rather than years. You will die.
This is not a "touching this thing is extremely dangerous proceed with caution" scenario. This is a "if you breathe in this dust, it will kill you slowly and painfully" scenario.