INITIAL FIRE EDGE i INITIAL 



BARRIER 



LOCATION 



CHOSEN 



SYMMETRY 



FIRE REACHES 

 INITIAL BARRIER 



B 



SECOND 

 BARRIER 

 LOCATION 



JNITIAL 

 i^' BARRIER 

 COMPLETE 



BOTH SEGMENTS 



c 



Figure 4A. — The first step in controlling a rapid head fire is the construction of a 

 barrier at distance '"a" ahead of the initial fire location. B: Construction of the 

 second segment of the barrier starts when the fire reaches the first segment. C: Work 

 proceeds against the flanking fire^ by direct attack, when the ,fire reaches the second 

 barrier segment. 



Clearly a best choice exists for the value a/ r io) . If "a" is too small, the fire 



' 



will reach the barriers very ciuickly, and contact with the edp.e of the fire will occur 

 at a position near tlie line of symmetry; if tliis contact occurs where inequality 8 is 

 violated, control will not be possible. If "a" is too large, the initial barrier will 

 be uiniecessari ly long and mucli time will be wasted before contact with the fire edge is 

 made; indcad if "a" is sufficiently large, tlie second barrier will contact the edge of 

 tlie fire at a point to the rear of the fire flank, resulting in much unnecessary burned 

 area . 



13 



