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Fire behaviour _1.pptx

  1. Wildland Fire Behavior I - An Introduction
  2. Objectives  Identify the environmental factors which govern the behavior of wildland fires.  Describe four methods of heat transfer. Upon completion of this unit, the student will be able to:
  3. The Origin of Fire All fires have at least one thing in common: An original ignition point.
  4. The Fire Triangle Three elements must be present in the correct proportions for an ignition to occur. Fuel Heat Oxygen
  5. The Fire Triangle Remove any one of these elements, Fuel Heat Oxygen and the fire goes out.
  6. 01-03-S290 Components of the Wildland Fire Environment WEATHER TOPOGRAPHY FUELS
  7. 01-04-S290 WEATHER  Temperature  Relative Humidity  Atmospheric Stability  Wind Speed and Direction  Precipitation Components of the Wildland Fire Environment
  8. Components of the Wildland Fire Environment 01-05-S290 TOPOGRAPHY  Elevation  Position on Slope  Aspect  Shape of Country  Steepness of Slope
  9. 01-06-S290 Components of the Wildland Fire Environment FUELS Fuel Loading Size and Shape Compactness Horizontal Continuity Vertical Continuity Chemical Content
  10. Fire Triangle  Heat – Types of heat transfer  Radiation  Conduction  Convection  Mass Transfer – Preheating of fuels  Fuel Temperature  Sun vs. Shade
  11. Heat Transfer For combustion to be sustained and for fires to spread, heat must be transferred from one fuel particle to the next. This happens 3 different ways: Conduction Convection Radiation
  12. Heat Transfer Methods CONDUCTION: Transfer of heat from one molecule to another. CONVECTION: Transfer of heat by movement of air. 01-11-S290 RADIATION: Transmission of heat by electromagnetic waves.
  13. Conduction Conduction is the transfer of heat from one particle of fuel directly to another. Wood is a poor conductor of heat, so conduction is the least important means of heat transfer in terms of wildland fire behavior.
  14. Convection Convection is the process of “hot air rising”. It is what makes smoke columns rise and assists in upslope fire runs. It is potentially the most dangerous of the three heat transfer methods.
  15. 01-16-S290 Transport of Firebrands by Convection
  16. Radiation Radiation is the transfer of energy through space, in the form of light and heat. Radiant heat will dry and potentially ignite surrounding fuels.
  17. Mass Transfer Heat transported in the form of firebrands.
  18. Transport of Firebrands by Wind 01-17-S290 WIND
  19. Transport of Firebrands by Gravity 01-18-S290
  20. Fire Triangle  Oxygen (air, wind) – Needed for combustion – Contributes to the rate and direction of spread (wind) – Contributes to spotting problems