I have no accident record for any one with the surname BUBNASH. Moreover the state of PA only required nonfatal accidents to be reported through the year 1940 which is why I have no accident record for John Bubnash.
Newspaper articles would be your best source of information. You might try to find another newspaper other than the Uniontown Herald.
The most common cause of this type of accident was an unexpected "fall of rock".
“Mining Accidents U.S., Canada, New Zealand and Australia”