LACROSSE, Ind. — The cause of an Indiana grain elevator blast that injured four employees in April has been ruled an accident.

The exact cause of the explosion in the northwestern part of the state could not be determined, but it was narrowed to the possibilities of a slipping belt, electrical malfunction in the wiring or static electricity, said Aaron Rust, the fire chief in LaCrosse.

Three possible causes were not able to be ruled out by evidence gathered during the course of the investigation, he explained. Whatever the source, grain dust inside the elevator provided the combustion.

"The initial fire ignited the dust in different areas of the elevator’s structure, causing three to four explosions within the elevator," Rust added.

The April 16 blast was powerful enough to blow a large hole out of the east side of the 175-foot-tall elevator and a smaller hole on the opposite side of the concrete structure.

All four of the injured employees – including the most seriously hurt, Jonah Pacione, 19, and Emilio Galicia, 34 – are home and progressing well in their recoveries, said Kevin Still, CEO for Co-Alliance, from its headquarters in Avon, outside Indianapolis.

Pacione and Galicia, who both were originally listed in critical condition, spent several weeks at St. Joseph Burn Center in Fort Wayne before being released.

The elevator has since merged with a new and much larger Co-Alliance feed mill 40 miles to the south in Reynolds. The merger was already planned before the blast and the elevator, which had been in LaCrosse for decades, will be torn down with leveling of the structure expected to be finished before the end of summer, said Shawn Lambert, Co-Alliance safety and risk manager.

"Co-Alliance is committed to cleaning up the site as soon as demolition bids are evaluated and the site is released by regulators and insurance carriers," said Lambert.

Most of the dozen or so employees at the LaCrosse elevator have been placed at other Co-Alliance operations. Other buildings on the site not damaged by the blast, including two grain silos, will likely be sold, said Co-Alliance Chief Financial Officer John Graham, who also works at the Avon office.

In 2013, a Co-Alliance-owned grain elevator just 15 miles away in Union Mills exploded, causing 67-year-old James Swank to fall over 100 feet from a work platform to his death. The cause of that blast was ruled a mechanical failure on a conveyor that generated enough sparks from the breakdown to ignite the grain dust.

The Union Mills plant was rebuilt and is still undergoing improvements. The LaCrosse plant was used to mill corn that was put into a mixture of soybean meal and other ingredients to produce livestock feed for farmers within a 50-mile radius.