(Reuters) - Four contractors were burned on Sunday in an explosion at an Arizona pet food factory, a fire department official said.
The workers were welding in a grain elevator at the Nestle Purina plant in Flagstaff at around 4:30 p.m. when grain dust caught fire and sparked an explosion, said Flagstaff Fire Department Captain Bill Morse.
One worker was airlifted with life-threatening burns to a local burn center and another was transported with serious burns by ambulance to the same facility, Morse said.
One of the other workers was transported to a nearby hospital with moderate burns, while the last contractor was treated at the same hospital and released, Morse said.
"As soon as they lit that welding torch, that was just enough to light up some of that dust," he said.
No one else was injured in the explosion and there was no fire, although the blast was strong enough to blow open a steel door at the bottom of the elevator, Morse said.
The grain handling industry is considered "high hazard," due partly to the risk of fires and explosions from the accumulation of combustible grain dust, according to the U.S. Occupational Safety and Health Administration website.
Flagstaff is about 150 miles (240 km) north of Phoenix.
(Reporting by Curtis Skinner in San Francisco; Editing by Alan Raybould)