Subject: Corrections to FFE Fire Behavior Calculations
Name: Stephanie Rebain
Date: 2004/08/18
Variants affected: All Variants with FFE

Description: The FFE fire behavior calculations were updated.  A
correction was made to the value of HPA (heat per unit area) used in 
estimating the torching index.  Previously, the HPA value for fuel model
10, not the selected fuel model, was being used.  In addition, the 
calculation of crown fraction burned for passive crown fires was updated
to match the method used in Nexus.  One of the coefficients in the crown
fire intensity / flame length relationship was adjusted to match Nexus 
and research publications.

Impact on Users:  Users may notice a difference in potential and 
simulated fire behavior, which may translate to a difference in fire
effects.  The torching index will either be higher or lower, depending
on the fuel models selected.  In some cases, this change in torching
index may cause surface fires to become crown fires and vice versa.  For
passive fires, the crown fraction burned and total flame length may be 
different.  For active crown fires, the flame length will be slightly
lower.

Files:
fire/base/src/fmcfir.f - added an argument that passed in the correct hpa
                         value, added some debug code, updated the 
                         calculation of crown fraction burned and final
                         spread rate for passive fires
fire/base/src/fmpofl.f - altered the calls to fmcfir and fmfint, altered 
                         the crown fire intensity / flame length relationship
fire/base/src/fmburn.f - altered the calls to fmcfir and fmfint, altered
                         the crown fire intensity / flame length relationship
fire/base/src/fmpocr.f - added some debug code
fire/base/src/fmfint.f - added some debug code, added an argument to 
                         pass in the call type, so an additional call to
                         fmfint was needed for the new crown fraction
                         burned calculation

