Five experts in building structures and grain dust explosions say early indications point to a blast as a likely cause of the International Nutrition plant collapse that killed two men Monday in Omaha.
The official investigation could take up to six months. But looking at photos of the disaster for The World-Herald, the experts said signs of an explosion include building panels that are bowed out and other panels that appear to have been forced away from the building by a blast, possibly because they were designed to release pressure.
The experts also said it is unlikely that such a catastrophic structural failure came first, given that the building was in regular use with no apparent problems.
“You would have to have some kind of explosive force to cause that to collapse,” said Robert Schoeff, a retired Kansas State University professor who spent decades tracking and studying dust explosions.
The fact that many people who were at the plant did not report hearing an explosion does seem unusual, he said. But, Schoeff said, “I've seen cases where employees on the other side of the building didn't hear anything. There are a lot of strange phenomena about these explosions that are hard to explain.”
The crash came “pretty fast, and pretty much without warning,” said Jay Davis, a building inspector and the superintendent of the City of Omaha's Permits and Inspection Division. He has toured the scene.
Davis couldn't say whether there had been an explosion. But he agreed the cause was likely something other than an initial structural failure.
“Buildings that have stood as long as this one has, they just don't fail without reason,” he said.
The initial call for help described a “building collapse and explosion,” acting Capt. Chris Hopkins of the Omaha Fire Department said Friday.
However, on the day of the incident, Omaha fire officials declined to say whether there had been an explosion, saying that would be up to investigators from the federal Occupational Safety and Health Administration to determine.
OSHA investigators, a spokesman said, are focusing on structural deficiencies as well as a dust explosion as possible causes of the collapse, which killed a maintenance mechanic and a custodian and sent 10 other people to hospitals with broken bones, burns and damaged organs.
Agricultural engineer Carlos Campabadal, on the faculty at Kansas State University's department of grain science and industry, said a dust explosion could be strong enough to topple a concrete grain bin structure.
Looking at a photograph of the damage, he said, “It definitely has to be some sort of explosion.” He said there is a strong possibility it was a grain explosion, given the nature of the business.
International Nutrition manufactured animal feed supplements. Workers were unloading a 51,000-pound delivery of a ground-corn product in the moments before the incident happened, according to the Iowa trucker who made the delivery.
Grain dust — including dust from the product being delivered, a byproduct of ethanol production — is considered highly combustible and is a reason OSHA considers grain handling a “high hazard industry.” There have been more than 500 explosions in U.S. grain-handling facilities in the past 35 years, and those have killed 184 people and injured 677, OSHA said.
William Field, a professor of agricultural and biological engineering at Purdue University, said photographs of the scene appear to show wall panels bowed out and blown off, which he said could indicate a blast.
Field studies grain entrapments as well as grain dust explosions, which he said have become more scarce. “But when they do happen,” he said, “they're very significant, with a lot of structural damage and multiple fatalities.”
He said he would not speculate on what happened in Omaha, but he said one area where explosions occur is in the bucket elevator system used to transport the grain vertically from where the truck unloads it to the top of the grain elevator structure. Sparks from friction can ignite dust in the air.
Investigators will study building plans, physical evidence, witness accounts and computer control data, said Russ Ogle, a chemical engineer with the California-based Exponent consulting firm. Ogle investigates fires and explosions at industrial plants.
While there are some similarities among cases, causes aren't uniform or obvious, Ogle said. He wouldn't guess at the cause “without taking a close look at the physical evidence.”
“Equipment, materials, the building construction — all these things can play a role,” he said.
It's a complex case, with clues lying in victims' memories and buried in a tangle of concrete, cinder block and steel.
Accounts from witnesses and victims of what they saw, heard and felt Monday morning will offer important clues for investigators trying to figure out what went wrong. There was a rumble, witnesses said. They recalled a blackout. A spark. An explosion. A big ball of fire, and black smoke.
Company officials have declined interview requests but said through a public relations agency they are working with investigators, insurance carriers and others on finding the cause of the accident. International Nutrition employee Kim Nguyen, director of international sales, told some news media it was not an explosion, and wind could have caused the collapse.
But the weather was mild the morning of the collapse — 35 degrees and calm, according to the National Weather Service.
Omaha did see heavy winds in the days preceding the accident. There were wind gusts of more than 50 mph on Jan. 14, 16 and 18, just shy of severe thunderstorm warning speeds of 58 mph. Other structures in Omaha suffered wind damage in the gusty days leading up to the plant collapse.
And as the wind blew, temperatures seesawed. On Sunday, Jan. 19, the day before the accident, temperatures ranged from a low of 17 to a high of 65 degrees — 5 degrees above the previous record high for the day.
But those wind speeds and temperature fluctuations should not have affected an industrial plant, said Omaha structural engineer Kip Squire of TD2 Engineering & Surveying, who is not involved in the investigation. He said local building codes specify a design load that can handle 90 mph winds, and the nearly 50-degree temperature variation would be considered normal for this part of the country and would have been taken into account on the initial design of the building, built in 1974 and remodeled in 1998, according to city records.
Squire said the events suggest some other cause preceded the collapse.
“A building that has been up there that long, I wouldn't think it would collapse on its own and cause an explosion,” he said. “I would think it would be the other way around. It would be very, very surprising if it collapsed on its own due to the wind.”
The Douglas County assessor considered the building of “average” quality and in “good” condition.
OSHA's last inspection was in 2011 and turned up six violations, unrelated to the structure, that were subsequently resolved.
The City of Omaha does not inspect a building's structure once a certificate of occupancy has been issued. The most recent building permit issued for the property was for plumbing work in 2006. “We've had no issues that I could find in our files,” Davis said.
It was not immediately clear whether the Omaha Fire Department had recently inspected the grain elevator structure or the dust collection system, both of which are under its jurisdiction, state officials said. A Fire Department spokesman said the deputy fire marshal was not immediately available to discuss the property. A Fire Department clerk said her only record of inspections at the property was a 2009 fire alarm system inspection.
A Metropolitan Utilities District official said it replaced the water main that serves that industrial area in 2009, and has had no water main breaks in that area that could have undermined the stability of the ground under the plant. MUD also said a gas leak has been ruled out.
A dust explosion is not an automatic conclusion, however, at least as a primary cause. Dust explosions are growing more rare.
Statistics compiled by OSHA show there were 80 grain-handling explosions between 2001 and 2010, down more than half over two decades earlier.
Schoeff said the industry as a whole has done a much better job of preventing dust explosions. Companies that handle grain do a better job of controlling dust and also monitor equipment that could provide an ignition source.
Schoeff's tracking data showed Nebraska once led the nation in dust explosions, with 59 between 1958 and 1990. But over the subsequent two decades, the state had only 13 — a drop Schoeff attributed to an expanded state inspection program launched by the State Fire Marshal's Office in the 1980s. “Your people really worked hard at it, and it's paid off,'' he said.
That office, however, does not oversee Omaha fire protection efforts, and the program would not have affected this plant.
One other trend Schoeff has noticed over the years: As large grain elevators did a better job of preventing dust explosions, a higher percentage occurred in food and feed mills.
Experts said five elements are necessary for a dust explosion:
It takes oxygen. It takes an ignition source, which could be a spark caused by welding, a cigarette or friction such as in the bucket elevator system on a grain bin. It also takes a combustible dust — and the dust must be dispersed in some way in the air.
“Something has to trigger its release — it could have been some other event inside the building to have caused the dust to be shaken loose,” said Guy Colonna with the National Fire Protection Association.
Finally, the combustion process must be confined in some way, he said. That could be a small space or an entire plant building, depending on how much fuel there is.
Experts say a dust explosion sometimes involves two blasts. The first might stem from another fuel source and cause a flame front or pressure front, which then shakes loose and ignites the dust for a second blast. It all happens in a fraction of a second, Colonna said, and not everyone on-site may hear the blasts, if the sound is muffled by the noise of equipment running or by plant or office walls.
Many Omaha plant employees interviewed have not mentioned hearing an explosion, at least initially. Instead, they've described the building falling in around them, and then a fire.
One worker who was on an upper floor when the grain bin tower collapsed theorized there may have been a structural problem with the tower because of the weight it was carrying and perhaps recent high winds.
“I didn't hear an explosion,'' he said. “I'm pretty sure an explosion didn't cause the collapse.''
The trucker who delivered the corn Monday swears there was no explosion.
“There was no such thing,” Larry McElhinney said.
He had unloaded 50,000 pounds of distillers dry grains, and having filled one storage bin, climbed back into his rig to wait for employees at International Nutrition to switch to a different bin so he could unload the last 1,000 pounds. He was working a number puzzle when debris began raining down onto his cab.
McElhinney had delivered to International Nutrition before, and called the Omaha feed manufacturing plant “one of the better, cleanest places we go to.”
Now he considers himself lucky to have come away alive.