Why harvesters are at risk of catching fire

06 Jan, 2011 01:11 PM
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Dr Graeme Quick, an internationally-recognised agricultural engineer and harvester expert, was engaged by the GRDC to look at the causes of combine harvester fires.
Dr Graeme Quick, an internationally-recognised agricultural engineer and harvester expert, was engaged by the GRDC to look at the causes of combine harvester fires.

FARMERS are being urged to adopt new safety measures to help prevent the risk of their header catching fire during harvest.

Following a spate of incidents in Southern Queensland, Northern NSW and South Australia’s Yorke Peninsula, the Grains Research and Development Corporation (GRDC) commissioned Dr Graeme Quick, an internationally-recognised agricultural engineer, to conduct an investigation into the causes of harvester fires.

Each year more than 1000 harvesters catch fire, of which about one per cent, or approximately 12 harvesters worth at least $500,000 each, are burnt to the ground.

“Australian broadacre harvest conditions are arguably the most hazardous in the world for fires,” Dr Quick said. “So far no lives have been lost due to combine harvester fires, fortunately.”

Dr Quick’s report found there was a perception among farmers that the number and frequency of harvester fires was increasing.

The incidents in South Australia during the 2009/10 harvest prompted an inquiry from the Country Fire Authority, which along with many farmers in the region, blamed static electricity build-up on machinery.

“There is no doubt that static electricity builds up on parts of combines under some conditions, but it is concluded that it is highly improbable as a primary cause of fires,” Dr Quick said.

“Controlled environment tests by Chilworth Global in New Jersey have been carried out on finely-ground crop residues. It was found that the minimum ignition energy (MIE) required was 500 milliJoules in a continuous arc.

“The energy in an electrostatic spark from a harvester may not exceed around 150 milliJoules. Even at 500 mJ, a spark (unlike a continuous arc) did not ignite crop dust in air in the controlled experiments.

“Unless there are volatile gasoline vapours present, it is highly improbable that there is sufficient discharge energy from an electrostatic discharge source to ignite crop materials on a combine.”

Dr Quick’s research was consistent with a United States report which found that 77pc of harvester fires started in the engine bay with the remainder initiated by problems with failed bearings, brakes, electricals, or from rock strikes.

“The most common cause of harvester fires is material collecting on hot engine components such as the manifold, exhaust and turbocharger,” Dr Quick said.

“Crop materials collecting or clumping on those components can ignite, then embers can drop down or are blown around the machine and into the crop causing spot fires or smouldering.”

The temperatures out of a diesel engine exhaust pipe can reach up to 650 degrees Celcius, and surface temperatures on these components can approach 500 deg. C.

And while crop residues can ignite at temperatures above 200 degrees C, Dr Quick noted that insulating muffs can bring the surface temperature on the exhaust down to 250 degrees C or lower.

The world’s two biggest machinery manufacturers, Deere and CNH, have also employed full time staff to address the fire and safety aspects of their designs.

“That consciousness has been sharpened by the mandated shift in diesel engine emission controls – Tier 3 & 4 engines run hotter, so there is more potential for fires around the engine,” Dr Quick said.

“Both companies have given detailed attention to reconfigure the battery and fuel tank areas. Airflow around the engine bay has been changed to better ensure material is blown off the manifold, turbo and exhaust areas by the 100+ km/h wind from the radiator fan.”

But a number of other factors are also required for a harvester fire to take hold:

  • Some material is heated to its ignition temperature and MIE;
  • There is an adequate supply of oxygen (air); and
  • There is a propagation path for the fire. Fire is possible under many initiating conditions, but conditions are often unsuitable to propagate a fire.
  • There are also four essential factors in the paddock:

  • Relative humidity
  • Ambient air temperature
  • Wind speed
  • Crop type and condition.
  • Farming practices can also increase the risk of harvester fires. Desiccating crops eliminates nearly all moisture-bearing green crop materials which might otherwise dampen fire risks, while crops such as lupins and pulses emit a fibrous dust which can accumulate around hot parts of the machine and catch fire.

    “Harvesting low enough to gather such a low-growing crop as lentils inevitably results in stone strikes,” Dr Quick said.

    “Some stones can cause sparks when struck by metallic harvester front components, such as the skid plates or even the sickle bar. Sparks from this have caused fires.”

    Dr Quick said the key to avoiding harvester fires was diligence in clean-down and inspection, and in the highest fire-risk periods paddock work should be postponed.

    “All operators should equip their machines with at least two fire extinguishers,” he said. “A high capacity air compressor with air lances should be on board or at hand.

    “Regular blow-downs are essential and in the worst conditions a blowdown may be needed as frequently as every half hour.”

    Dr Quick developed the following checklist, which has been endorsed by the GRDC, for reducing fire hazards on combine harvesters:

  • Recognise the factors that contribute to fires: relative humidity, ambient temperature, wind, crop type and conditions. Stop harvest when the danger is extreme.
  • Redouble service, maintenance and machine hygiene efforts at harvest on the days more hazardous for fire. Follow systematic preparation and prevention procedures.
  • Avoid the accumulation of flammable material on the manifold, turbocharger and exhaust system. Tailwinds can disrupt the radiator fan airblast that normally keeps the exhaust area clean.
  • Lookout for places where chafing of fuel lines, battery cables, hot wires, tyres, drive belts etc, can occur.
  • Avoid overloading electrical circuits.
  • Periodically check bearings around the front and the machine body. Use a hand-held digital heat-measuring gun for temperature diagnostics on bearings, brakes etc.
  • Drag chains or grounding conductors may help dissipate electrical charge but are not universally successful in all conditions. In certain conditions a drag chain could even start a fire from rock strikes.
  • Use the battery isolation switch when the harvester is parked. Use vermin deterrents as vermin chew some types of electrical insulation.
  • Observe the Grassland Fire Danger Index (GFDI) protocol on high fire risk days. Don’t jump to a conclusion that static electricity is a cause of fires; the evidence doesn’t support this as a prime cause on harvesters.
  • Maintain two-way contact with base and others.
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