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90.1 Custom Fuel Models <br />Developing a custom fuel model is an exercise in modeling. It is not possible to directly <br />use field data to define a custom fuel model. A person who is developing a custom fuel <br />model should have a basic understanding of Rothermel's model (Burgan 1987; Burgan <br />and Rothermel 1984). The Intermediates tab of SURFACE includes fire model interme- <br />diate values such as relative packing ratio, heat source, heat sink, etc. (Figure 60). <br />F.d &M69.e I W.A%.W I memo.. I SW. I B.* own+ I WWA O*w i n.p. j Fad oraM I Arora ompuh IP-GOdpa <br />r I1eaAFud 1�[ein�le <br />r G'heaetee.deliseRd]Iniseae <br />f iireFalMrittareotii�nttiea <br />r chou"14k Wv <br />F Baticllnm <br />r Pack.* Bao <br />r uwn p dmRsno <br />r DeadFwlFaaeeea7rota <br />r l wPw Rnvfiw <br />r 1Wd$ftw <br />t' �opeFap.r <br />r }imt Saic <br />r Flame Enid. Tin <br />P rkwt 1P H* <br />Relati*-r Packing Ratio <br />padW4 cao Md. tao altl. r.dbsd p61mp raw to an Ophcommpada*r6. Oen <br />bf Aen,op). Thk c As' &W vibe id Rod`taWR sw&ts Bre spM W model <br />Bra. tidier d.m..lsoeds apw=num pdscw <br />Leo Madel► <br />Input ; Now <br />OWPW - sUSFAc <br />lire Uro <br />• <br />1."kh! <br />• Vm%blt Ieeme <br />• <br />a TaW, Index <br />of <br />.tr <br />Figure 60—Intermediate values help you understand the fire model for use in developing custom <br />fuel models. <br />Once it has been determined that none of the standard 53 fuel models is appropriate, a <br />common way to develop a custom fuel model is to make adjustments to an existing fuel <br />model. Rather than selecting the option Fuel is entered as Fuel parameters (Figure 59), <br />it is best to open the example worksheet FueiModeling.bpw or FuelModelingMetrie. <br />bpw, both of which are designed with six decimal places for fuel load values to avoid <br />possible issues with round off (Section 5.2). Click on the Initialize from a Fuel Model <br />button on the worksheet and select one of the fuel models in the list to fill in values on the <br />worksheet (Figure 61). Fuel model 1 (short grass) has only fine (I -h) dead fuel. A related <br />custom fuel model might be developed by adding some live herbaceous fuel and reducing <br />the 1-h load. Fuel modeling will involve producing tables and graphs to examine influ- <br />ence of changes on calculated surface rate of spread and flame length. It is also helpful to <br />took at the intermediate values (Figure 60). <br />72 USDA Forest Service Gen. Tech. Rep. RM RS -GTR -249. 2010 <br />