Even though there have been huge leaps in the safety of flour mills and granaries, there were 115 airborne grain dust explosions reported in the United States between 1994 and 2004 resulting in 16 fatalities and 137 injuries. The majority of these explosions (58) were attributed to corn dust in granaries or refineries, while only eight happened in flour processing or storage operations. The 11.5 accident average for the ten-year span is actually more than the previous 11.28 average for the previous 35 years. The data from the United States Department of Labor for 1970 to 2010 indicates that “Over the last 40 years, there have been over 600 explosions in grain handling facilities across the United States, which have killed more than 250 people and injured more than 1,000" making it the second leading cause of death in granaries behind suffocation.
Chester, Illinois Flour Mill Silos, April 2010
Although the flour silo explosion at the ConAgra Silos in Chester didn’t result in a massive death toll like some of the other disasters on the list, it is here as a reminder that, although we have come a long way in making our granaries safer through preventative engineering, there is no way to make them 100-percent accident free. The accident severely injured three workers that were clearing out a clogged leg in the silo that has been smoldering. When one of the workers unclogged the leg, the exposure to oxygen and release of airborne dust caused a catastrophic explosion that blew tons of concrete from the top of the silo and shook homes for miles around. The tremor it caused was compared to a recent earthquake in the area, and most people who felt both said that the silo explosion was much more violent.
Davenport, IA Flour Mill Explosion, May 1975
The explosion at the Davenport river flour mill (formerly the old Robin Hood flour mill) in 1975 only killed two workers, but hospitalized seven others. The explosion caused windows to shatter 18 to 20 blocks away. The official cause of the disaster was a grain powder fire although the details were never publically revealed. This, and several explosions in 1977, led to wholesale changes in the safety systems in the 1980’s. These included the requirement of lubrication schedules for all equipment, confinement systems to control an explosion if one occurs, and a strict no smoking policy. Further changes were employed in various amendments to the legislation. These included the implementation of oxygen suppression systems.
Litchfield, IL Flour Mill Explosion, Mar 1893
Initial accounts of the explosion at the Litchfield, IL Flour Mill in 1893 blamed the fire and resulting devastation on a boiler malfunction. Later evidence pointed to employees overlooking a major safety precaution, the dust machine. It was not properly secured and allowed flour dust to escape into the confines of the rolling room. When a fire broke out in the bran room, a night watchman tried to put out the fire. The water pipes attached to the emergency hydrant were not in proper working order so he could not put out the fire. It quickly spread to the adjoining rooms. When it reached the rolling room, the airborne dust exploded. The damage destroyed 40 homes and 2 blocks of local businesses. The damage to the mill alone was over one million dollars (roughly equivalent to 24 million dollars today).
This explosion directly resulted in more stringent regulations for the fire suppression systems in all mills as well as regular inspection and required training for all employees that would be using the dust machine.
Washburn “A” Mill; Minneapolis, May 2, 1878
The Washburn “A" Mill explosion of 1878 is the most infamous flour mill explosion in history. It killed 17 people, pulverized the main building, and devastated seven more. The explosion was so powerful that it broke windows as far away as St. Paul and limestone blocks from the building were thrown into yards up to eight blocks away. There was no dust catching filter in use because, although there had been several explosive incidents in Europe, no one believed that the dust could actually catch fire and explode.
At the time of the explosion, the “A" mill was the largest flour mill in the country. The explosion served as a wakeup call for owners of other mills. This was the definitive proof they needed to start eliminating the flour dust from their operations. It led directly to the use of an 1845 invention, the dust machine, which collected dust from milled grain.
Westwego, LA Grain Elevator Explosion, Dec 1977
Even though the Washburn explosion is the best known of all flour mill explosions, the explosion in Westwego, Louisiana had more than double the number of fatalities. With 36 deaths attributed to this one disaster, it is the worst flour mill explosion on record. Most of the deaths occurred in a control room where employees were trapped and crushed as the giant silos collapsed onto them. The explosion occurred due to a buildup of grain dust in a highly oxygenated area when a static electrical discharge ignited the head and exploded. The fire blew the top off from the silo and the fire spread to 48 adjacent silos. Major reform to the building codes for all future sites came from this event. Each silo must now have heat sensors at various levels tied directly to a control room where temperatures can be monitored in real time. Pressure sensors were also required to monitor and help prevent the thermal expansion of grain dust, and all control rooms were moved away from the silos with the minimum distance being at least twice the height of the silo.
When we look at flour dust explosion, history shows us that our incremental improvements have resulted in safer mills and granaries, but this doesn’t mean that death tolls are coming down. In fact, over the past 55 years the death toll has remained steady- as have the number of accidents. This means that even with all of the engineering advancements that have been made, employees must still be aware of and follow all safety procedures to make the systems safe.
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