CHAPTER 5 



FIRE-DANGER RATING 



USE OF FIRE-WEATHER INFORMATION 



Fire-danger rating techniques have been 

 used widely in National Forests and other protec- 

 tion organizations for more than 20 years. Each 

 general region has developed its own system of 

 integrating into meters or tables the primary 

 factors that influence the start and spread of 

 fires. 



Prior to 1956, Interior Alaska had no formal 

 system of fire-danger rating, and thus no basis 

 upon which to build a fire-danger rating system. 

 Fire control officers relied upon their personal 

 judgment and experience to estimate the effect 

 of the fire weather for the current day and for 

 the previous several days on preparedness and 

 suppression activities. The younger men in the 

 expanding fire control organization needed a re- 

 liable guide upon which to base their decisions. 



The Intermountain fire-danger rating sys- 

 tem was introduced in 1956 without any modifi- 

 cations as an interim measure in order (1) to 

 interpret weather information in an orderly fash- 

 ion for use in fire control work, and (2) to ob- 

 tain research data during the period of the sys- 

 tem's operation for eventual incorporation into a 

 better system, which would be designed in ac- 

 cordance with local conditions (Hardy and 

 Brackebusch 1959). 



After using the Intermountain system for 

 2 years, experienced observers noted that the 

 burning index meter did not react to actual field 

 changes as fast as was necessary. Appalachian 

 slats were then substituted for the half-inch dow- 

 els (fig. 38) that comprise the fuel moisture in- 

 put to the Model 8 meter. This change permitted 

 the burning index to react faster, more in keep- 

 ing with the rapid changes in the fire-carrying 

 characteristics of the finely divided, high surface- 

 area-to-volume Alaskan fuels. 



Information from the Model 8 meter can be 

 used satisfactorily by referring to the rate-of- 

 spread computations shown in table 1 1 (Barrows 

 1951; Fahnestock 1951). For Alaskan fuels and 

 bu rning conditions, however, the perimeter in- 



crease figures can be only approximate and rela- 

 tive until data from local research make possible 

 a more reliable revision. 



To explain the above statement: fires 

 burned through black spruce stands in Interior 

 Alaska at a rate of 120 to 600 chains per hour 

 when the burning index was between 28 and 

 37, 5 while in southern Idaho fires burned through 

 cheatgrass stands at a rate of 142 to 248 chains 

 per hour when the burning index was between 

 78 and 93. 6 



By 1960, 14 fire-weather stations were op- 

 erating throughout Interior Alaska. No great 

 increase in the number of stations is likely in the 

 near future because of the limited number of 

 personnel available. Reliable observers, located 

 near centers of use, with access to adequate 

 long-distance communications are as necessary 

 as proper locations and well-maintained instru- 

 ments (Hardy, Syverson, Dieterich 1955). 



The following tabulation compares the num- 

 ber of stations and areas involved in Interior 

 Alaska and Region 1 of the U.S. Forest Service. 7 



Alaska 



Region 1, 

 USFS 



Number of stations 

 Total area 



involved (acres) 

 Average area per 



station (acres) 

 Area ratio 



14 



225,000,000 



18,750,000 

 1 



175 



32,000,000 



182,857 

 100 



Even with the large number of stations in 

 Region 1, the personnel are continually endeav- 

 oring to interpret fire weather from a permanent 

 fire-weather station to specific sites on going 



5 With half-inch sticks, or 33 and 59 with slats. 



6 Traylor, R. E. Processed report of a study of eight fires in 

 southern Idaho, 1959; on file at Northern Forest Fire Labora- 

 tory, Missoula, Montana. (Burning index based on half-inch 

 sticks.) 



7 Montana, northern Idaho, northeastern Washington, and 

 northwestern South Dakota. 



41 



