The Granite Mountain/Speculator Mine disaster of June 8, 1917, occurred as a result of a fire in a copper mine, and was the most deadly event in underground hard rock mining in United States history. Most men died of suffocation underground as the fire consumed their oxygen; a total of 168 miners were killed. The Butte, Montana copper mines were at full wartime production to support the US in World War I. Miners had been seeking improved working conditions, as they were at high risk.