Comparison of Fuel Consumption Between High Intensity and Moderate Intensity Fires in Logging Slash

h igh ]n tens i t r1 i r r :s . t I igh in te l . . i t r f re .cou] t1beu:e lntroduction 'lhousands of rcles in the Pacilic \.nthrrest are brLrned each rear as an inLegral part oi lorest rnanagernent. Slash Lurnirrg is Lrseri to preparc hancslctJ sitcs lbr planting nnd to recluce lilcliire hu:rrd-s. Air qualitr is directlv irnpacted bv -inolie tr(rnl slash f ires. As a rcsul l . scrcral sludics havc bccn undeltaken h predir ' l the consurnlrt ion of fuels dur-ing s1ruh bulning. Emissions that are leleasecl into thc air cluring slash burning can be controlled bv . r r d ' r t : r ' " l , r r 5 . r ' ' , 1 ' r r " r r i 1 , ' . l . r t n g i r r 1 , ' , n . ' r r n p t i u n . Certain ignit ion techni( lues are shor|n lcr clccrcasc fucl consumption (National \t iltliire Coor cl inating Croup 1985) and lo irnpfove air qual i tv bv decrea-. ing erni-"sions. In a t9tt . l f i lot . lucl). the Fire arrcl Air Resource N'[anagemcnt Projcct. l)acif ic \olthlest Research Station. L SDA Forest Service. me,rsuled i i rel tonsurnption in rapidLl igdited. high intensiLv f ircs. R('sults frorn lhc pi lol studv inrlicatecl that high intensitv lires consumed less fuel than cl id lolcl intcnsitr f i rcs. r ' i th thc majoritl ol c-on-rurnption taking place during the llam| | r g phasc . The purposc ol this papr:r rras to fur-thcl investigate fuel consumption c[Lling high intensitl f i res. The objectire \ \as to . lelernrine i f high f ire t , n i l i , i " r i f , . r n t r r " d r r ce t u . . ^ , r ' n l ' t i ^ I J , n ' r r 1 ' r r , 1 t , , r r , " l r r r t ' ' l ' i ' r r . ' r i r i F . A nrorll las clcvclopccl to drtcrmine if dilfer ences in the thenn: eDvirulnent c(ruld explRin dilfelerrces in fuel consumption bctrrccn high and nrodcl-atc inlcnsitv f i rcs. Literature Review and Background Thc majori t l of shsh burns in thc Northlest ale ignited r i th hand-held torc,hcs. using str ip hracJ]58 Northrrcst Scicncc. \ 'ol . 65. No. ,1. 1991 iires. This ignit ion techiclue inr 'ohes ignit ing one Io scvcral arJjaccnl st l ips of fucl l r t onc t ime. As the i i re spreads. these str ips burn together in the flarning stage rrhich is charar:Lerized bv the mor.crrrerrt of r isible f larnr through the ftrcl . As thc f laming i iont passes :urd the i i re "dies-dorn." enterirrg thr srnolclering,ctage (Nalional Si i l t l f i rc CoorJ i r ' a l i r r 3 ( r , . r p l q R 5 r . r l r r \ r . r i ' ' i \ . t r i t ' s alc ignitcd. Thc proccss is slor ' . and onlv small Rrea-c of the unit are in the llarning stage at r)ne l ime. Fire intensit ies (heat release per area pcr t jmc) r: lngc frorn lol to moderate. dependinpi on the ignit ion rate. This faper refers to such burns as rroclcr-atc inlcnsi lv f i rcs. High intensitr iires difier'liom rnoderate intensiLv f irrs irr se\eral \ravs. lhc rrosl obvious bcing the method of ignition. A unit must be mass-ignited to achiere a high inlensit \ f i re (CoLrnLrvrrrarr 1964). \ ' l lss ignit ion can be aclonpl isheri bv hantl l ighting or bv helitorch: the iE(nited strips interact quicklv. and Lhe errLire unit is sinul lancoush in f lamcs. lhe resr t is longer llalne length-s. thich resrLlt irr liolent f i r ' 1 , , 1 . r \ i , , r . f i n r ' l r i l l . . . r n , l h i g l r i r r t o n . i t i e . B ' " r ' . ' . l n , I Da r i t I o , . 1 t , l , u l l r " i n t e r r i t i e i n Lefrr ls of 'st i l i f -slep or a discontinuous-Lvpd'scalc. Thcl suggcst this discontinuous scalc occurs because i ire intensitv increases lathel abrupth from onc lcrcl to anolhcrlcrcl of considcrabh higher intensitv. Aho\e Lhis abfLrpL step is the region of high intensitv lires. oiien acconpanied b,v large , ^ r , \ , , r i , r , , . ' l ' . r r , r r ' B r " r r r l u i ; r T l , i I ' J t , F f r , fcrs to such burns as high irltensitl llres. \ l u t u f t h , 1 , r " r J r \ l , r r n , , 1 , i m l ' t i o n studics ha1'c investigated woocll iuei and dulI (consisLing ol the fermenli t l ion and humus lavcr-s) consurnption iiom nloderate inten-sitv fire-s. ['oocll fuel consumption studics havc bccn completed in ldaho. NIontana. arrcl Ontal io (Norurn 1977. fr lcl lac 1980. Brorln et al. 1985. l lc inhart l t et ol. 19891. Duff consumption -rtudies hare been unrlcrtakcn in cl j f fcrcnt gcographic locations and l irest tvpes (\ ian \\ 'ngner 1972. , \hcrrcr 1975, \orunr 197i. Sandhelg l9f i0. Bronn er al. l9B5) ' l 'he ! i rc and Air Rcsource Nlirragement PfojecL. Pacif ic \orthr\,est Research Stadon. has conJ . r , t ed -e re r . r l " oo , l ' I ' r " u , J J ' . t i " , ' n ' , ' , , t ' r : , ' r ' studies lbr logging slash using modelatc intcnsi lr ' f i r-c in $r:slcrn Oregon and $eslern Srlshi]r€iton (Sandberg and (Jttnrar 1983. Ottmar 198,tr, and Ollnlar et al. 191]5). The-se studies provicle a ba-sei ine aElainst lhich thc fucl consrlrnption dal i l for this stucl l ol high intensitr i i les rdl l be com larecl. Data collected in the l irc ancl Ail Rcsource 1\lanagenent Project -stLrdies Nele the most relevant to thc arca and condil ions under rrhit 'h the high intensit l l i res $rrc studicd. l 'o simpli fv the compar-isr;n between rnodelate intensitv l l res and high intensit l f i rcs. lhc sanrc variable-" rele mclsurerl and the sarne rrethodohgv las used. .-Sandberg and Ottmar (1983) founcl that Lhe b , t p r , , l i , t " r " f l r l g . " , , , , , 1 ' f r r l ' , , ' n u r n l ' t i o r r . neasured bv diameter rcduction, is lhe intrrnal moistule of large lop1-c. In atternptinpi to preclict fucl consurnption Lv cornbustion stages (f laming and srnoldeling). Ottmar lI9B,1) did a prcliminan sturir ofrr 'ooch fucl thrt foruscd on pfed;ct ing ()nstrrnpl ion dLrr ing the l larning st:rge. \Vart l (1983) had eadl ibuncl that cmission fac tols differ fcrr flarning combustion and smolcle ng combllst ion. Ottrnar' (198lJ spe.Lrlales that consumption oi -mr l l t L ' . , ' ' r r . nu t l , , l r r r i ns r l , . f l : r n i r ! r ag ' : and ihat dianletel reduction of largc. rrooclr l i rcls cluring thc f luming stagc is dependent on lhe amount ol small luels consumed. Ottmar suggcsts that the rat io of f laning vcr-sus srnolr ier ing t 'onsurnption i i laming proport ionl for largc logs is , 1 , p n , J ' n t u r t l ' l t ) t ) l r , ' r r r / i . l , " r r . r n r p t i " n . Consunrption of duif ras fcrund Lo be affected bv the btrrning of loodv i i rel-". depending on duff moistulc (Ottmar et eL. l9B5l. Tto dif felent lnoistufe condil ions \\ere l ;und to desfl ibe hr. ' duil consumption conclitions. Duff rcrluction for l et clLrff ( less than 25 davs sirrce 1.3 cm oi rain) is dcpcnclcnt on lhe total heat load sLrlrpl iecl bv the combuslion of large wood,v luels. DulT recluct ion for rnoist duif hnore than 25 clavs since l-i:l cm of rain) is depenclent on l l re duration. lhich is dctcrmincd b,r cl iameLer edLrct ion oi the large l irels. I ' rel iminarv lcsults lr-om l larrr irrg duff consLrmplion studies suggest hat l larning cluf l ' rcduct ion is depcndcnt on f larning diarneler reduction of toodr' fLrel (Ottrnar' 198.1). Fucl cronsumlrt ion drrr ing hiplh intensitv l i les is not lel l documeltcd rnd is prirnarih qual i tal ive raLhef than quanti tat i |e. The revie\\cd l i tcraturc contdins discrepancies in r ihethel high intensit_v f ires hale rnore or less fucl consumption than modcrdtc intensi lr f i res. -\er 'eral earlv workeh oLserved that alrnost all luei las consumcd on high intensitv f i r-cs (Clar and Chatten 1966. Bvrarn 1966. Brown and D:rvis I973). C)thcl obscnations suggest LhaL les-< fLrel i-q consurned on high intensin iircs (Hullcv anrJ Tavlol 197rtr. Ottrnar [personal cornmunicationl) or that there is no cl i l fclcncc in fucl consumption bel$'een high iniensitv and mod erale intensitv f i res (XlcRae Lperson commumcalronl l , [rhat factors might cr ist in the thelmal enrironmenl of a high intensitl ilre that rroulcl causc a rliffcrence in fuel crrnsrrrnption/ One possible iirc tol is the duration of hcat sLrpplir:d lo wood,v fuel. l i rc clurat ion on se\eral high intensitv f i res has been observed as being verv sholt: f i -om I to 2 hours for units ranging fronr 24, to 200 ha (Finnis 19i0. Hur' lev anclTavlor 1974. and Ottrnar' [pcrsonal conrnrunicatiorr l)Fire clulat ion fol moderate intensit l f i lcs langcs bcL\feen:1 tr):16 hours. with an a|erage of B to 12 hours. clcpcnding on fuel rnoislufe anal t inre of r ear (Ottmar lpersonal com' mun i ca t i on l ) . The fale of c(rnsLrmption could be :rnother l i : rc tor inl luencing f ircl colsumption during high int r r i t \ f i r . I he | r r l e o l soo , l r l . r ' , u | l u rnp l i o r l bas bccn rneasured in laboraton and l ield experiments. and thcrc appcars lo be a \\ ide range " f , un .u rn l , t i o r r f J l i , ' , l , , , r h r , , , dF a l c i r l . n i l \ :rnd high intensitr fires pcr' 2.5 crn of diamctcr rcdl lct ion. LaboraLorv ronsunrption rates varied Irour 52 minutes (Schailer 1967t to 8 minutcs (Anderson 1969. and I i .-s. Forest Produts Labo r J t o r \ l ' , ; I r . 1 " i , 1 , 1 , , 1 , . , ' . r t i , , n , , f , , , r r . r r r n p t i , , r r rates ranged 1fom 3.8 to I I minutcs olr rnodcr-alc inlcnsi l ! f i rcs. lo 2.5 nrinLrtes on high intensit ! f i re-q {Ottmar [pelsonal conrmunication] lmd CountNman 1969 ) . ' l t rgc ro r r l r nd" r i l l re fe r ro r lea t l rood ' n r te r ie l benreen i .6 lnd 22 . i l .d iD d i lmeter . rl00-lnn,r kli rs ro d tinFhg nal rlN i,,r uurd"ood djaDeters , , 1 2 . 5 1 , , i . 6 ( ! r 1 l ) . r n i n g . r d l . 1 9 1 ; r . Fuel ConsLrmrrt ion in Hieh and \ 'Lrderate Intensitv Slash I ' i res 159 Thcre is a disparit,v in previous studv results concern;ng fuel consurnption and rates of ftrel consumption in high intensitv and rnodelate inten-qitv i ires. This studl seeks to resohe that dispafi ty bl determinirrg u,hether thcrc is a dif ference in {uel consumption brtween moderate intensitv fire-q and high intensitv f i res. Study Areas and Methodology