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Understanding Causes of Combine Fires Leads to Solutions

Wednesday, August 31, 2022
filed under: Harvest/Storage

New Knowledge of What Leads to Most Combine Fires, Including Notoriously Fire-Prone Crops Like Sunflower, Leads to a Less-Stressful Harvest Season
This article is reprinted, with permission, from Nuseed’s SUCCEED magazine, Volume 6, Annual 2022 edition.
combine in field

South Dakota farmer Steve Pfeiffer had used all the old tricks to prevent combine fires during sunflower harvest. They didn’t work.
        “We’d tried everything. Asbestos kits around the manifold.  Done the old chain drag thing.  None of these successful” Pfeiffer recalls.  He was so frustrated with the problem he ended up reducing his sunflower acreage partly because “we were just having so much damn trouble with fires, it was a headache.”
        Then Pfeiffer had a neighbor with a combine fire that went out of control.  Afterwards, through word of mouth, he heard about an after-market add-on kit reputed to prevent the problem.  He decided to give them a try on two of his three combines.
        “We bought two (kits) and never had a fire in those machines.  But the other combine was plagued with fires all year long,” Pfeiffer says.
Taking Action on Combine Fires
        Pfeiffer purchased “FireStop” kits from Harvest Fire, a company started by Dan Humburg, a retired South Dakota State University (SDSU) agricultural engineer professor.
        Humburg is an industry expert in what causes combine fires in the first place, especially in sunflower, expertise he gained while leading an SDSU research project funded by the South Dakota Oilseeds Council.
        Sunflower, Humburg says, had become the “poster child for the concept of a fire in a combine.”  Growers reported stopping multiple times a day to extinguish smolders in their hopper, usually with a few squirts from a water bottle.
        “If you can imagine the stress of driving your car down the road and knowing that at any moment it’s going to catch fire?  Well, you wouldn't like to start a long trip under that circumstance.  [Farmers] have to start harvest with the idea, ‘I’ve got two weeks of this, riding the front edge of the seat smelling air, waiting for the next fire to start,’ ” Humburg says.
        Humburg quickly discovered that sunflower growers had already realized through trial and error that if they went too fast, fires would start, even within minutes of a minor increase in engine load.
        That confirmed Humburg’s suspicion that a hot exhaust system was a likely culprit in ignition.  But what was it about sunflower that made it so volatile as compared to other crops in the first place?
A Dusty Fire-Storm Potential
        In their lab studies, Humburg’s SDSU research team discovered that sunflower pith is ground up as it moves through the threshing system, creating a cloud of friable dust that hangs in the air and clings to all parts of the combine and engine. Was the dust the culprit?
        “If you look at those particles apart underneath the microscope, they look like Swiss cheese.  They're just big pockets of air and a little bit of material.  It’s all primed with air and ready to burn,” Humburg says.
        In ignition tests, sunflower pith dust sitting on a hot plate rose in temperature when the plate was set as low as 500 degrees F, a much lower temperature point than ground-up corn stover or soybean material.  Meanwhile, sensors deployed on a combine had recorded temperatures as high as 800 degrees on exhaust components when the combine was well loaded, well above the ignition point for sunflower pith dust.
        Humburg had even heard reports of a sunflower dust cloud seeming to explode. One farmer told him he had stopped and was cleaning off his engine with an air compressor when his father drove by on another combine and sucked some of the dust cloud into his radiator.
        “All of that dust in the air lit up in front of him.  He said it looked like you lit a spark on the Fourth of July, there were small sparks sailing and swirling in the air all around,” Humburg says. “That’s what we believe happens when they're in the field under the right conditions.  When they cross the engine-load threshold that brings the exhaust temperature to that level, it ignites as soon as it hits the turbo in the air stream.  And now you have this blast of air going there that’s carrying sparks.”
        Those sparks settle into the hopper, most typically on the left side of the machine where the air blast is pushed, starting a small, growing burn unless the farmer catches it — usually by the scent of smoldering sunflower seeds, Humburg says.
        Humburg’s research turned into add-on kit prototypes that filter the air that hits the exhaust system, preventing the dust from being ignited in the first place. This turned into a business after he retired from SDSU in 2016, largely because of a steady barrage of requests from farmers. Harvest Fire currently sells FireStop kits for multiple older Case IH and John Deere combine models.  Also, they can create kits for models they don’t have per request (go to
        Humburg says that combine manufacturers have “paid attention” to the SDSU work, and newer combine models may be less likely to ignite.  However, it can depend on the model, the crop and the grower’s specific conditions.
Resting Easier During Harvest
        Humburg’s research and subsequent solution have led to the happy result of better options and less worry for sunflower growers, says John Sandbakken, executive director of the National Sunflower Association.
        Humburg’s add-on kits have a good reputation among growers, but other solutions are in the marketplace now as well, including installing an air tower (chimney) on the combine’s air intake to help bring in clean air instead of dust.
        And farmers now know what works best — and what doesn’t — to prevent fires.  Humburg discovered during the SDSU research phase that it is unlikely fires start due to static.  So, dragging a chain to discharge static to the ground likely won’t make any difference in preventing fires because static isn’t causing the fires, as Pfeiffer and many other farmers had already discovered.
        But keeping the dust off the hot elements of the engines, slowing down so their engines don’t run so hot or even harvesting during the evening when conditions are cooler and there’s more moisture in the air can help, Sandbakken says.  Purchasing add-ons like the FireStop kit or air towers give growers even more security.
        “It’s controllable.  Follow the safety practices of blowing off your combine.  If you have an older combine, get one of Dan’s kits or one of these air intakes.  You will probably have very few issues,” Sandbakken says.
        Sandbakken says the word does appear to be getting out, at least to sunflower growers.  The frequency of fires during sunflower harvest seems to be going down while fires in other crops appear to be occurring more.  A likely cause of that may be more extreme hot and dry conditions during harvest time, meaning the ignition temperature of other types of crop dust.
        “What’s happening is combine fires are showing up in other crops, like soybean and even grains.  It’s the dust because it is so dry,” Sandbakken says.
        Brent Heidecker, an Alberta, Canada, farmer, struggled with fires in his annual canola harvest.  Like with sunflower, he noticed the big problem appeared to be the dust created in the threshing process. The longer the canola was swathed before being combined, the more combustible the crop seemed to be.
        They had small smolders every year, but the turning point was three years ago, losing the combine his 78-year-old father was driving.
        “By the time he realized the combine was on fire, he had time to get out, but that was about it,” Heidecker says.  Fed up, Heidecker purchased the FireStop kits.
        They still follow all the same safety protocols, including keeping a water pump on their grain carts just in case. But, they haven’t had a fire since they installed the kits.
        “We basically quit worrying, where before it was constant,” Heidecker concludes.
6 tips for combine safety
        Most farmers are well aware of the potential danger of combine fires, but it is always a good idea to review your procedures well ahead of harvest time, says John Nowatzki, a North Dakota State University (NDSU) extension agent and agricultural machine systems specialist.  He recommends farmers implement the following fire-prevention policies, no matter what crop they are harvesting.
#1. A Fire-Prevention Mentality —
Slow down and don’t cut corners.  “Farming accidents most of the time occur because you get in a hurry,” Nowatzki says. “You’re trying to get done, you’re competing with the weather. That’s when mistakes happen.”
#2. Keep It Clean —
The most important thing is to keep the engine clean. Use an air compressor or leaf blower to blow dust off, Nowatzki recommends. There is no set rule for how often to clean off dust, some farmers do it every time they unload. Nowatzki advises at least daily.  “If it’s a fire that has started in the combine itself, it’s almost always because that dust has collected. They don’t clean it often enough,” Nowatzki says.
#3. Consider Harvest Conditions —
The dryer and hotter it is, the more likely to have a fire. Consider combining early in the morning when there is a little bit of dew on the crop.  “When you’ve got everything really dry, that’s when you see the fires,” Nowatzki says.
#4. Prevent Field Fires Caused by Auxiliary Vehicles —
A pickup truck’s exhaust system is close to the ground. If it’s hot and comes into contact with dry, combustible crop material, a fire can easily ignite. Make sure to park on soil where there is no vegetation.  “Exhaust systems under vehicles are a big issue. On a combine or a tractor, you don’t have to worry about that,” Nowatzki says.
#5. Service Your Fire Extinguishers —
When a fire does happen, make sure you’re prepared. “Fires realistically don’t happen too often.  Make sure your fire extinguishers are updated yearly,” Nowatzki says.
#6. Call 911 First! —
Farmers tend to think when a fire does get started, they can control it themselves. While that may end up being the case, better safe than sorry.  “Call 911 first, before you do anything,” Nowatzki says.
For more information on harvest-time fire prevention, NDSU has a downloadable checklist for farmers on their website —
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