SALT LAKE CITY (AP) — A massive fireball soared into the sky in the central Utah desert after officials blew up 11 derailed tanker cars containing propane and biodiesel.

The controlled detonation Sunday night was the safest way to deal with the explosive material, Juab County Undersheriff Brent Pulver said Monday about the decision by state and federal agencies, including the U.S. Environmental Protection Agency.

The derailment occurred Saturday when 24 of the 165 cars of a Union Pacific freight train went off the tracks. One car landed on its side and was leaking propane.

The conductor and engineer were not hurt in the derailment, whose cause was not immediately known. Nine rail tankers carried propane, and two had biodiesel.

Officials initially planned to move the rail cars but worried that leaking propane could cause an explosion and injure the crew.

Pulver posted photos online showing the fireball about 75 miles (120 kilometers) south of Salt Lake City, where the derailment occurred. The nearest town is Eureka, with less than 1,000 residents, about 15 miles (24 kilometers) away.

The fire burned for several hours.

"It was impressive. There is no other way to put it," he said.

Crews were cleaning up the site and planning to bring in heavy equipment to move the rail cars that are damaged beyond repair, he said.