I was a mile down in a Canadian mine during a cave-in alarm. We all moved to the emergency shelter (basically, a tube drilled into the rock, with metal pipe emplaced for reinforcement and benches on either side to sit, with supplies). We had to shelter-in-place for a while, and it was an odd feeling when the vault door was locked shut with us in there. Fortunately, it was just a drill that lasted an hour.
Because the mine is noisy and no alarms could be heard, and lights wouldn't be seen in all the tunnels and with flashing lights on equipment, the way the alarm is given is via odor. They pump a stink through the ventilation system.
So these miners will have some time to twiddle their thumbs...I hope they're all safe in the end, though.