The Tuesday explosion of a wood pellet manufacturing plant in Fremont that killed a worker and two young girls was caused by a dust fire, an official said Thursday.

The State Fire Marshal's Office confirmed the explosion at the Horizon Biofuels plant was an accident. On Thursday, fire officials revealed the cause of the explosion was an accidental dust fire. The explosion, which happened on Tuesday just before noon, claimed the lives of three people, including Dylan Danielson, 32, and two young girls.