Charles C. Roberts, Jr., Ph.D., P.E.

As the harvest season comes to a close, insurers of agricultural equipment are often left with the headaches associated with combine harvester fires. The modern self propelled combine harvester (combines the harvesting and threshing operation in one apparatus) is a complex and expensive piece of machinery often priced in excess of a quarter million dollars. When a fire develops in one of these beasts and is not controlled by the operator early on, a total loss can occur, since rural volunteer fire departments may take a considerable amount of time to reach the remote location of the combine. Figure 1 is a schematic drawing of a typical self propelled combine harvester. The header shears the grain and feeds it to the grain conveyor. The threshing cylinder, in concert with the separating cylinder, separates the grain from the straw. The grain is stored in the grain tank while the straw is taken by the straw walkers to the straw spreader which chops up the straw and sends it out into the field behind the combine.

Figure 1

Case studies are useful in explaining the various causes of fire related losses in combine harvesters. Figure 2 is a front view of a combine showing evidence of a fire origin in the engine compartment. The vehicle was combining corn when the fire started. It should be noted that the fire occurred in October, but the subrogation unit did not call for an inspection until January. To blunt the spoliation argument, inspection of the vehicle soon after the loss is desirable.

Figure 2

Figure 3

Figure 3 is a close-up photo of the bell housing on the back of the engine showing a faulted wire (white arrow) that had shorted to ground at the bell housing. Inspection of the wire in an exemplar combine showed the wire to be unsupported and resting on the bell housing. The wire was subject to chafing (Reference 1) over time, which damaged electrical insulation, resulting in the short circuit related fire. Good engineering design of wiring harnesses includes proper support of the wires to prevent wear from chafing. This was absent in this case, suggesting a high probability of recovery from the manufacturer. Not all wiring insulation breakdown in combines is a result of chafing. Figure 4 shows insulation damage from rodents (Reference 2). It is known in the industry that rodents chew on polymer insulation, causing insulation breakdown and a possible fire. Proper storage of the combine may be a factor with respect to rodent infestation. Other types of biologic intervention such as bird nests (Reference 3) on hot engine components can cause fires and be a result of poor system design, such as lack of proper guarding.

Figure 3

A common cause of combine fires is straw or chaff build-up during harvesting. Straw and other combustible dust tends to accumulate in the machinery and can be ignited by a variety of ignition sources, especially in exceptionally dry weather. Figure 5 shows such a build-up, which is often addressed in operator’s manuals. Typical requirements by manufacturers are to clean out the residual chaff once a day. Subrogation potential is low for those cases where the operator failed to follow the cleaning recommendations in the manual.

Figure 5

Figure 6

In Figure 6, the red arrow points to a fuel leak near a fuel line support clamp. The fuel line leaked fuel as a result of a fatigue crack in the fuel line. Ordinarily, the subrogation unit from the insurance company would be talking to the manufacturers on this claim. However, the insured owner of the vehicle noticed the leak prior to the fire and failed to correct the problem, possibly reducing the degree of recovery from the vehicle manufacturer. The yellow arrow points to several faulted wires that are a result of the fire and not a cause.

Figure 7

Figure 7 is a view of the side of an engine block on a combine, which is at the origin of the fire. A connecting rod had failed and punched through the block as indicated by the red arrow. This expelled hot oil vapor, which was ignited by a variety of possible ignition sources in that area. Many insurers would deny a claim of damage to the engine as a result of a “mechanical failure” but would extend coverage to that part of the machine damaged by fire. Mechanical failure can be a result of wear out, improper design, improper manufacturing, improper remanufacturing, improper repair and lack of maintenance. In this case, engine wear out on an old vehicle was to blame, suggesting a decreased chance for recovery.


1. “Wire Chafing, a Cause of Electrical Fires,” Claims Magazine, April 1999.
2. “Rodent Damage to Automobiles,” Claims Magazine, December 1996.
3. “Biologic Intervention Can Cause Fire,” Claims Magazine, September 2002.