Mass-flow rate

n. The rate of canopy fuel consumption per unit time per unit area of a canopy profile.

 

  • Discussion

 

Mass-flow rate is an important factor affecting the propagation of crown fires.  It is a product of canopy bulk density (kg m-3) and the rate of spread of the crown fire (m sec-1).  One way to conceptually picture mass-flow rate is to imagine the flaming front as stationary (rather than the forest as stationary and the flaming front moving though it) and to imagine the forest moving through this stationary front as on a conveyor belt.  The mass consumed per unit time through any square meter of the flaming front depends on how fast the “conveyor belt” is moving (the crown fire rate of spread) and the density of the forest that is moving along the conveyor belt (the canopy bulk density).  

 

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Van Wagner (1977) empirically determined the minimum mass-flow rate required to sustain a crown fire as 0.05 kg m-2 sec-1.  Using this relationship and a model to predict crown fire spread rate, the minimum wind speed needed to sustain a crown fire can be calculated. Alternatively, the canopy bulk density below which a crown fire is unlikely can be calculated. See Agee and Skinner 2005, Scott and Reinhardt 2001, and Van Wagner 1977 for further discussion.

 

  • Units

     

    Preferred units for mass flow rate are kg/(m2-s).

     

  • See Also

  • References

    • Agee, J.K.; Skinner, C.N. 2005.  Basic principles of forest fuel reduction treatments.  Forest Ecology and Management. 211: 83-96.

    • Scott, J.H.; Reinhardt, E.D. 2001. Assessing crown fire potential by linking models of surface and crown fire behavior.  Res. Pap. RMRS-RP-29. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

    • Van Wagner, C.E. 1977.  Conditions for the start and spread of crown fire.  Canadian Journal of Forest Research. 7: 23-34.

     

  • Notes

    • Author 

      James Agee, Professor of Forest Ecology

      University of Washington