Explosives
The explosives that detonated in the explosion were stored in a shanty at the quarry. Due to a delivery the previous day, there was approximately 2,450 pounds of dynamite in the shanty at the time of the explosion. The foreman at the quarry, Thomas Fitzpatrick, reported a small explosion, similar to a normal quarry blast, immediately before the large one. He suggested that a single stick of dynamite may have been accidentally dropped. The resulting small explosion could have set off the entire shanty. The true cause of the explosion was never determined.
Read more about this topic: Sibley Quarry Explosion