0.5 1.0 1.5 2.0 



SUPPRESSION RATE /FORWARD RATE OF SPREAD 



But tliis series of figures also tells another story of sensitivity. Note that 

 a small "error" in barrier placement is inconsequential so long as A/V^,, V^/V^, and n 



are properly chosen. But improper choice of fire shape or rate variables can lead to a 

 catastrophic miscalculation. For example, assume that -0.2, n = 2 describes 



the shape of the forward edge of the fire. So if A/V^, is estimated to be 1.0, then 



from either figure 7 or figure 8, a choice of a/r (0) in the range 0.22-0.25 is 







indicated. Such a choice would result in a burned area of no more tlian 5.5 times the 

 initial area, and a final perimeter approximately 1.9 times the initial perimeter. 

 However, if the value of tlie suppression rate had been overestimated by 10 percent or 

 the forward rate of spread underestimated b\' a similar amount, we should refer to the 

 curves labeled "0.9" in figures 5 and 6. On these curves, any value of a/r {{)] less 

 than 0.28 results in no solution. In other words, any barrier location closer than the 

 critical value of 0.28 r fO) from the forward edge of the fire will not allow 







sufficient time to the crew to achieve a "capture" condition when the work reaches the 

 edge of the fire. 



Because of this sensitivity and the severity of sucli an error, an "optimum" choice 

 for the first barrier location is not of practical significance. Some substantial 

 "margin of safety" must be considered in the selection of the initial barrier location 

 whenever A ^ V^, . For this reason, table 5 is presented, sliowing the burned area and 



perimeter ratio for the same conditions as in table 4, except that the initial barrier 

 location is chosen to be twice the value which minimizes the burned area. This table, 

 therefore, incorporates a "margin of safety" of 100 percent in the deviation from 

 optimum. A comparison of the values in tables 4 and 5 reveals that the "penalty" 

 paid for this margin of safety is not severe in most cases. 



17 



