The Mammoth Mine disaster or Frick Mine explosion occurred on January 27, 1891 just after 9:00 AM in the Mammoth No. 1 mine in Mount Pleasant Township, Westmoreland County, Pennsylvania. Newspapers reported that fired was ignited by a miner’s oil lamp, resulting in the deaths of 109 men and boys. Most of the miners were not killed by the force of the explosion, but rather were suffocated by the effects of afterdamp.
From approximately 1879 to 1889 the Mammoth No. 1 mine was owned by Colonel J.W. Moore Coke Company in Greensburg, PA. In 1889, the mine was purchased by The H. C. Frick Coke Company.
Accounts vary, but it is believe that 109 coal miners, mostly Polish, Hungarian, and Italian immigrants, were killed on the morning of the explosion. Seventy-nine of the victims are buried in a mass grave at St. John’s Union Cemetery. In the early 2000s, two Pennsylvania Historical & Museum Commission markers and a pair of personalized headstones were added to the site.