Table 11. — Average initial rate of spread' according to fuel type, slope steepness, and burning index 



at site of fire 2 



Fuel rate of 



Slope 



Burning index 



spread type 



steepness 3 



1-10 



1 1 -20 



21-30 



31-40 



41-50 



51-60 



61 



-70 71-80 



81 -90 



91 -1 00 





Percent 









Perimeter 



increase 



(chains 



per 



hour) 







Low 



n in 

 U- 1 U 



U 



1 



1 



1 



l 





 z 



z 





 z 





 O 



A 



4 





i i oc; 

 1 1 -/j 



U 



1 



1 



l 







4. 



O 



Z 



n 

 



J 



A 



4 



A 

 





o/. cn 

 zo-oU 



1 



1 



O 

 Z 







z 



Q 

 O 





 O 



4 



4 



A 

 



n 

 





1 -/ 



1 



O 



z 





 





 



4 



it 



a 



A 

 O 



-7 







y 



1 O. 

 1 





Over 75 



2 



3 



4 



5 



6 



7 



8 



10 



15 



20 



Medium 



n i n 



n 



1 



1 



1 





 z 



z 







z 





 



A 









1 1 -ZD 



1 



1 



1 



z 





 z 





 







4 



A 

 



-7 



/ 





ZO-OU 



1 







z 





 z 



Q 

 O 







4 







A 

 



Q 



O 



1 n 

 1 U 





C 1 7ET 

 J 1 -/ J 



Z 





 



j 



>< 



4 







A 

 O 



-7 







y 



1 

 1 O 



1 A 

 1 O 





Over 75 



3 



4 



5 



6 



8 



10 



12 



15 



20 



25 



High 



n i n 

 U- 1 U 



U 



1 



z 



Q 

 O 



4 







A 

 O 



Q 

 O 





 y 



1 

 1 z 





11 1C 



1 1 - Zd 



1 



1 







4 



A 

 



7 



O 



y 



1 1 

 1 1 





1 7 



1 / 





0>^ rn 



zo-oU 



O 

 Z 





 z 



4 



O 



Q 



O 



i n 

 1 u 



1 z 



1 A 

 1 O 



1 O 



OA 

 Z4 





C 1 7C 



O 



n 

 



O 



O 



y 



1 O 



1 



i 

 1 y 



or 

 ZD 



OR 

 Zo 



O.O 

 JO 





Over 75 



4 



5 



10 



15 



20 



25 



30 



40 



45 



60 



Extreme 



n i n 

 U- 1 U 



1 







4 







a 

 



Q 

 O 



1 n 

 l U 



i 



1 A 

 1 O 



1 

 1 y 





ii o cr 

 1 1 -20 



1 



4 



O 



-7 





 y 



1 1 



1 A 



1 4 



1 

 1 y 



OO 



zz 



07 



Zl 





z6-0U 



z 



z 







Q 

 O 



i n 

 1 U 



1 z 



1 O 



on 

 zU 



OA 

 ZO 



TO 

 OZ 



O.Q 

 OO 





1 -/o 





 



n 



y 



1 



i /. 

 1 6 



1 y 



OCT 



zo 



dz 



A ~\ 



4 1 



t;n 

 OU 



An 

 OU 





Over 75 



5 



15 



20 



25 



30 



40 



50 



65 



80 



95 



Flash 



0-10 



1 



5 



12 



15 



19 



24 



30 



37 



46 



57 





11 -25 



1 



7 



17 



21 



27 



34 



42 



52 



65 



81 





26-50 



2 



10 



24 



30 



38 



48 



60 



74 



92 



114 





51-75 



3 



16 



38 



48 



60 



76 



95 



1 17 



146 



181 





Over 75 



5 



25 



60 



75 



95 



120 



150 



185 



230 



285 



'Average initial rate of spread refers to perimeter increase between discovery of fire and first attack. This rate of spread may 



be anticipated during the first 4 to 5 hours. 

 2 Table based upon study of 2,955 fires in National Forests, R-l, 1936-44. Values for very high and very low burning index 



have been estimated. 



3 General descriptions used in slope descriptions are: Level, 0-10 percent; Gentle, 11-25 percent; Moderate, 26-50 percent; 



Steep, 51-75 percent; Very steep, over 75 percent. 



fires or prescribed burns (Barrows 1951). It will 

 never be possible to have such an intensive 

 coverage of fire-weather stations in Alaska be- 

 cause of the sparse settlement, lack of perma- 

 nent personnel, and lower order of resource 

 utilization. However, for purposes not requiring 

 daily measurement, recording weather stations 

 may soon be used to fill in gaps at important 

 locations. 



Data collected from the present system of 

 fire-weather stations in Alaska have assisted re- 

 search personnel in understanding the general 

 fire-weather complex that characterizes Alaska's 

 interior. Fire-weather information presented in 

 this publication was obtained from two sources: 

 fire-weather stations and actual fire data. Use 

 of the system by fire control personnel has en- 

 abled them to understand the trend of fire- 



42 



