The Cymmer Colliery explosion occurred in the early morning of 15 July 1856 at the Old Pit mine of the Cymmer Colliery near Porth (lower Rhondda Valley), Wales, operated by George Insole & Son. The underground gas explosion resulted in a "sacrifice of human life to an extent unparalleled in the history of coal mining of this country" in which 114 men and boys were killed. Thirty-five widows, ninety-two children, and other dependent relatives were left with no immediate means of support.