Investigators say the blast that prompted evacuations near Union Pacific's massive railyard in western Nebraska last week appears to be accidental, but it's not yet clear what caused it.
The Nebraska State Fire Marshal's office is working with the railroad and experts from the Federal Railroad Administration to determine what caused a stationary container carrying perchloric acid that can be used to make explosives as well as a variety of food and drug products to explode last Thursday in North Platte.
