SOUTH SIOUX CITY -- Across Siouxland, grain bins and elevators tower over the landscape, a constant reminder of the grain harvested from the land.
On May 29, Siouxlanders were reminded of the potential hazards that come with storing and moving that grain. An explosion at the Andersen Farms elevator in South Sioux City injured and burned one worker and badly damaged the structure, leading to worries that it might topple and endanger nearby homes and residents.
Authorities have yet to release the cause of the explosion, though few would be surprised if it's determined that grain dust ignited and triggered the blast. Ignition of the highly combustible dust is a common cause of grain elevator fires and explosions.
That potential for danger likely can never be eliminated entirely.
"Grain elevators are designed to handle a tremendous amount of grain. Whenever grain is handled, it inevitably creates dust," said Alyssa Sanders, Nebraska deputy state fire marshal and public information officer.
But increased training and improvements in technology and elevator design have greatly reduced the potential for disaster.
From 1976-85, there were 143 deaths from grain elevator dust explosions in the United States, Sanders said. From 1986-2003, that dropped to 33 deaths.
In 2017, there were seven reported grain dust explosions at U.S. food and agricultural facilities -- five of them in grain elevators -- causing five fatalities and 12 injuries. That total was up from five explosions in 2016, but lower than the 10-year average of 9.3 explosions per year, according to a Purdue University Department of Agricultural and Biological Engineering report.
"The trend is reducing, but still it's occurring. The number is going down, but our aim is to make it stop," said Kingsly Ambrose, an assistant professor of agricultural and biological engineering at Purdue.
Eliminating grain dust would eliminate the risk of explosions, a task Ambrose acknowledges is a challenge. Until an effective and economical means of eliminating dust can be found, the best way to reduce the hazard is through increased worker training and preventive maintenance.
Aware of the nature of the product they deal with, many grain companies have stressed training and maintenance while engineers develop equipment designed to make grain elevators safer.
"It's hard to say you can prevent anything 100 percent. We can go a long way with things we're doing to prevent those explosions," said Brad Bousquet, vice president of safety and compliance with York, Nebraska-based Central Valley Ag Cooperative, which operates several Siouxland grain elevators.
A grain dust explosion damaged the company's Hinton, Iowa, elevator and injured two workers in March 2016. The facility has since been repaired and rebuilt with the latest technology and equipment, Bousquet said. In Hinton and other locations, the company does what it can to reduce the risk of explosions.
An explosion occurs when four conditions are met: grain dust is suspended in the air, oxygen is present, there's a confined space and, finally, an ignition source such as a spark from machinery.
The presence of oxygen can't be eliminated, and confined spaces are part of an elevator, Bousquet said. So the focus turns to reducing dust and monitoring potential ignition sources.
Bousquet said the company's workers routinely lubricate bearings that can overheat and check belts that can become misaligned and rub on surfaces, causing friction that can spark a fire. Hazard-monitoring equipment in grain conveyor systems contains sensors that detect heat, motion and belt speed. Any variance from normal operations, and the sensors can set off alarms and shut down the system.
Dust control systems built into grain conveying equipment help remove the flammable dust.
All that equipment continues to improve, Bousquet said.
"The technology continues to increase in hazard-monitoring equipment," he said.
Grain elevator design has also improved safety, Sanders said.
In many older facilities, the bucket elevator leg, the system that lifts grain to the top of the elevator to distribute it to the silos, is built within the concrete facility. Modern grain elevators are built with those bucket elevators along the exterior of the facility so that energy and heat from blasts can be released outward rather than contained within the facility.
"The major improvement has been to design new facilities so that the dust explosion is not confined within a concrete structure," Sanders said.
State and federal regulations demand that grain elevator operators meet specific requirements, including programs to reduce dust accumulation, sensors and motion-detecting equipment in bucket elevators, preventive maintenance programs, regularly scheduled inspections and dust collection systems designed to minimize explosion risk.
Prior to 2018, the Nebraska State Fire Marshal's office inspected commercial grain elevators and feed mills that are registered and bonded with the Nebraska Public Service Commission once every five years. It switched to a three-year cycle this year. Sanders said the Andersen Farms elevator was not inspected because it is privately owned.
Jens Nissen, Iowa Occupational Safety and Health Administration administrator, said his office performs random inspections, but not on a regular schedule. Grain elevator operators are required to follow the regulations.
"It's not often we have an explosion in grain facilities now," Nissen said. "Obviously there are failures in systems, whether that's a mechanical failure or a human failure. I would hope that we could get as close as we possibly could" to 100 percent prevention.