The Avondale Mine Disaster was a massive fire in the Avondale Colliery in Plymouth, Pennsylvania, United States on September 6, 1869. It caused the death of 110 workers, making it one of the largest mining disasters in Pennsylvania history. It started when a wooden coal breaker built over a shaft entrance to the underground mine caught fire. This shaft was the only entrance to the mine, and so the fire trapped and suffocated the workers. Among those who died were five boys ages 12 to 17, as well as two volunteers who suffocated while they were attempting a rescue.
One of the first global relief efforts occurred after the disaster, with donations for the widows and families of victims coming in from all over the world. Another result of the fire was the passing by the Pennsylvania General Assembly of legislation establishing safety regulations in the coal mining industry, making Pennsylvania the first state to pass such legislation. These laws mandated, among other things, that there must be at least two entrances to underground mines. The disaster also caused thousands of miners to join the Workingmen's Benevolent Association, one of the first unions to represent coal miners in the United States. Continuing labor and social strife in the Pennsylvania anthracite coal fields led to an increase in the activities of the "Molly Maguires", a controversial organization that conducted violent attacks against anthracite coal mine operators. These conflicts eventually resulted in the trial and execution of twenty members of the Molly Maguires in Pottsville and Mauch Chunk.