Vehicle fires resulting from hot surface ignition of grass and leaves

Paper #:
  • 2017-01-1354

  • 2017-03-28
One potential fire ignition source in a motor vehicle is the hot surfaces of the engine exhaust system. These hot surfaces can come into contact with combustible liquids (such as engine oil, transmission fluid, brake fluid, gasoline, or diesel fuel) due to a fluid leak, or during a vehicle collision. If the surface temperature is higher than the hot surface ignition temperature of the combustible liquid in a given geometry, a fire can ignite and potentially propagate. In addition to automotive fluids, another potential fuel in post-collision vehicle fires is grass, leaves, or other vegetation. Studies of hot surface ignition of dried vegetation have found that ignition depends on the type of vegetation, surface temperature, and on the duration of contact. Ignition can occur at surface temperatures as low as 300 °C, if the vegetation is in contact with the surface for 10 minutes or longer. At surface temperatures of 400 °C, ignition can occur in 3 minutes, and at surface temperatures of 500 °C, ignition can occur in a few seconds. We made measurements of the surface temperature at various locations along the exhaust system of a passenger vehicle, including on the catalytic converter, under different transient conditions. The temperature was measured using thermocouples welded to the exhaust system. These measurements showed that system components can reach 400 °C and that these temperatures can be sustained for minutes after the engine stops. These tests identify the conditions under which a fire can result when a vehicle comes to rest in contact with dried vegetation, such as after a collision.
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