The blast blew out the east side of the elevator tower just before 10 a.m. Company officials report that foul play has been ruled out by investigators.

Grain dust is highly combustible, and is the usual cause in grain facility explosions.

"We do not yet know the cause of the accident, but will work with the authorities in their investigation,” said Co-Alliance CEO Kevin A. Still in a statement.

One of the injured employees, Chris Ford, 28, was transferred Friday from Porter Regional Hospital in Valparaiso to the burn unit at Loyola Medical Center in Chicago. He suffered first and second-degree burns and was listed in critical condition, according to a company report. Jonah Pacione, 19, and Emilio Galicia, 43, were airlifted from LaCrosse to St. Joseph Burn Center in Fort Wayne. Pacione suffered burns over 30-percent of his body and remains in critical condition. Galicia is in serious condition with burns to 18 percent of his body, mostly to his hands, arms and face. The fourth employee, 34-year-old Craig Chase, has been released from Porter Memorial Hospital.

“Our thoughts and prayers are with the employees who were injured today," Still said in the company statement.. "We have notified their families and provided them the location of the medical facilities where their loved ones were taken for treatment."

He added that company personnel would be at the hospitals to help provide assistance "to the employees and their families."

In addition to the facility in LaCrosse, Co-Alliance has 10 other grain elevators in the northern and central part of Indiana, and one in Buchanan, Mich.

The company also operates a grain elevator in Union Mills where an explosion in 2013 killed James Swank, 67, who was knocked off a work platform that was more than 100 feet off the ground. A mechanical failure generating sparks that ignited grain dust was ruled as the cause of the 2013 blast. The Union Mills plant has been rebuilt and continues to undergo improvements.

The LaCrosse facility mills corn which is then mixed with soybean meal and other nutrients to produce animal feed sold to area farmers.

However, it was about to be closed, and operations consolidated with the company's new grain elevator in Reynolds, according to John Graham, chief financial officer for Co-Alliance, based in Avon, just west of Indianapolis.

Graham said the new facility is modern and more efficient and can produce a higher quality product than the site in LaCrosse, which had "50-year old technology."