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.
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 sunflowers, expertise he gained while leading an SDSU research project funded by the South Dakota Oilseeds Council.
Sunflowers, 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 sunflowers that made them 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 $5,950 for multiple older Case IH and John Deere combine models. In addition, they can create kits for models they don’t have per request.
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.
