Fire Management Today Volume 64 • No. 1 • Winter 2004

FireManagementtodayVolume 64 No. 1 Winter 2004

United States Department of AgricultureForest Service

FORECASTINGWILDLAND FIREBEHAVIOR:AIDS AND GUIDES

FORECASTINGWILDLAND FIREBEHAVIOR:AIDS AND GUIDES

Editors note: This issue of Fire Management Today is the third in a three-part series of reprinted articlesrelated to wildland fire behavior, some of them decades old. Although the articles appear in todays format,the text is reprinted largely verbatim and therefore reflects the style and usage of the time. We made minorwording changes for clarity and added metric conversions where needed. All illustrations are taken fromthe original articles.

Fire Management Today is published by the Forest Service of the U.S. Department of Agriculture, Washington, DC.The Secretary of Agriculture has determined that the publication of this periodical is necessary in the transaction ofthe public business required by law of this Department.

Fire Management Today is for sale by the Superintendent of Documents, U.S. Government Printing Office, at:Internet: bookstore.gpo.gov Phone: 202-512-1800 Fax: 202-512-2250

Mail: Stop SSOP, Washington, DC 20402-0001

Fire Management Today is available on the World Wide Web at .

Ann M. Veneman, Secretary April J. BailyU.S. Department of Agriculture General Manager

Dale Bosworth, Chief Robert H. Hutch Brown, Ph.D.Forest Service Managing Editor

Jerry Williams, Director Madelyn DillonFire and Aviation Management Editor

Carol LoSapioGuest Editor

Martin E. Alexander and Dave Thomas Issue Coordinators

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Disclaimer: The use of trade, firm, or corporation names in this publication is for the information and convenienceof the reader. Such use does not constitute an official endorsement of any product or service by the U.S. Departmentof Agriculture. Individual authors are responsible for the technical accuracy of the material presented in FireManagement Today.

CONTENTSForecasting Wildland Fire Behavior: Aids, Guides,

and Knowledge-Based Protocols . . . . . . . . . . . . . . . . . . . . . . . 4M.E. Alexander and D.A. Thomas

Forest Fires and Sea Breezes. . . . . . . . . . . . . . . . . . . . . . . . . . 12G.L. Hayes

Fundamentals of Fire Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 15H.T. Gisborne

Vertical Wind Currents and Fire Behavior. . . . . . . . . . . . . . . . . . 24John S. Crosby

Warning Signs for Fire Fighters . . . . . . . . . . . . . . . . . . . . . . . . 27A.A. Brown

Recognizing Weather Conditions That Affect Forest Fire Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Owen P. CramerMeteorological Problems Associated With Mass Fires . . . . . . . . . 34

DeVer ColsonSome Principles of Combustion and Their Significance

in Forest Fire Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37George M. Byram

Vortex TurbulenceIts Effect on Fire Behavior. . . . . . . . . . . . . . . 45James B. Davis and Craig C. Chandler

The Concept of Fire Environment . . . . . . . . . . . . . . . . . . . . . . . 49C.M. Countryman

Get the Most From Your Windspeed Observation. . . . . . . . . . . . . 53John S. Crosby and Craig C. Chandler

Atmospheric Stability Forecast and Fire Control . . . . . . . . . . . . . 56Rollo T. Davis

Downbursts and Wildland Fires: A Dangerous Combination . . . . . . 59Donald A. Haines

Estimating Slope for Predicting Fire Behavior . . . . . . . . . . . . . . . 62Patricia L. Andrews

Air Tanker Vortex TurbulenceRevisited . . . . . . . . . . . . . . . . . . . 64Donald A. Haines

A Trend Analysis of Fireline Watch Out Situations in Seven Fire-Suppression Fatality Accidents . . . . . . . . . . . . . . 66

Gene A. MorseLCESA Key to Safety in the Wildland Fire Environment . . . . . . . . 70

Paul GleasonHow ICs Can Get Maximum Use of Weather Information . . . . . . . 72

Christopher J. Cuoco and James K. BarnettBeyond the Safey Zone: Creating a Margin of Safety . . . . . . . . . . 78

Mark BeighleyFirefighter Safety Zones: How Big Is Big Enough? . . . . . . . . . . . . 82

Bret W. Butler and Jack D. CohenSafety Alert: Watch Out for Aircraft Turbulence! . . . . . . . . . . . . . 86

Billy BennettThe Consumption Strategy: Increasing Safety During Mopup . . . . . 88

Tom Leuschen and Ken FrederickAuthor IndexVolume 63 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Subject IndexVolume 63 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

SHORT FEATURESWebsites on Fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28The Blowup Fire and Firefighter Safety. . . . . . . . . . . . . . . . . . . . 33Wildland Fire Researchs Raison Detre . . . . . . . . . . . . . . . . . . . 92Guidelines for Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 93Photo Contest Announcement . . . . . . . . . . . . . . . . . . . . . . . . . 98First of Its Kind: A Historical Perspective on

Wildland Fire Behavior Training . . . . . . . . . . . . . . . . . . . . . . . 99

Volume 64 No. 1 Winter 20043

Firefighter and public safety isour first priority.

Volume 64 No. 1 Winter 2004Management todayFire

Aids and guides from the past,some illustrated here, canhelp improve the fire behaviorforecasting capabilities neededtoday in both fire use and firesuppression. See the articlesin this issue for descriptions.

The FIRE 21 symbol (shown below and on thecover) stands for the safe and effective use ofwildland fire, now and throughout the 21st century. Its shape represents the fire triangle(oxygen, heat, and fuel). The three outer red triangles represent the basic functions of wildland fire organizations (planning, operations,and aviation management), and the three criticalaspects of wildland fire management (prevention,suppression, and prescription). The black interiorrepresents land affected by fire; the emerginggreen points symbolize the growth, restoration,and sustainability associated with fire-adaptedecosystems. The flame represents fire itself as anever-present force in nature. For more informa-tion on FIRE 21 and the science, research, andinnovative thinking behind it, contact MikeApicello, National Interagency Fire Center, 208-387-5460.

On the Cover:

FORECASTING WILDLANDFIRE BEHAVIOR: AIDS, GUIDES, AND KNOWLEDGE-BASEDPROTOCOLSM.E. Alexander and D.A. Thomas

Fire Management Today4

an wildland fire behavior reallybe predicted? That depends onhow accurate you expect the

prediction to be. The minute-by-minute movement of a fire willprobably never be predictablecer-tainly not from weather conditionsforecasted many hours before thefire. Nevertheless, practice andexperienced judgment in assessingthe fire environment, coupled witha systematic method of calculatingfire behavior, yield surprisinglygood results (Rothermel 1983).

This is the third and final specialissue of Fire Management Today ina series of issues devoted to thesubject of wildland fire behavior.The first two issues contained 36articles dealing with wildland firebehavior case studies and analysespublished in Fire ManagementToday and its predecessors between1937 and 2000. These two issuescontained lead articles on variousaspects of those subjects (Alexanderand Thomas 2003a, 2003b). Notincluded in these two issues aretwo recent articles on fire behaviorpublished in Fire ManagementToday (Brown 2002; Cornwall2003).

By systematically reflecting upon our fire behaviorforecasts and the tools that helped us preparethem, we become the masters of fire behavior

models and not their servants.

C

Marty Alexander is a senior fire behaviorresearch officer with the Canadian ForestService at the Northern Forestry Centre,Edmonton, Alberta; and Dave Thomas isthe regional fuels specialist for the USDAForest Service, Intermountain Region,Ogden, UT.

This issue is devoted to aids,guides, and knowledge-based proto-cols involved in predicting wildlandfire behavior for safe and effectivefire suppression (Alexander 2000).It includes 21 articles publishedfrom 1947 to 1998. A recent articleby Weick (2002) that emphasizesthe importance of human factors inthe field of fire behavior forecastingcould have easily been included.

The Practice ofPredicting WildlandFire BehaviorMore than 50 years ago, Barrows(1951) outlined the basic conceptsof predicting or forecasting wild-land fire behavior that are still veryvalid today (see the excerpt onpages 67). As figure 1 shows, theprocess of judging fire behavior canbe divided into five simple steps:

Figure 1Judging fire behavior requires systematic analysis of many factors(from Barrows 1951).


We recommend that fire behavior analysts adoptthe framework of the After Action Review, as

described on the Wildland Fire Lessons LearnedCenter Website.

1. Basic knowledge. The founda-tion for judging probable firebehavior must rest on basicknowledge of the principles ofcombustion: What is necessaryfor combustion to occur? Whatcauses the rate of combustion toincrease or decrease? How maycombustion be reduced orstopped?

2. Forest knowledge. Three basicfactors in a forest areaweather,topography, and fuelsareimportant indicators of firebehavior.

3. Aids and guides. Several aidsand guides are available to assistin evaluating weather, topogra-phy, and fuels.

4. Estimate of situation. The prob-abilities for various patterns offire behavior are systematicallyexplored through an estimate ofthe situation based upon thecombined effects of weather,fuels, and topography.

5. Decision. The end product ofthe fire behavior analysis is adecision outlining when, where,and how to control the fire andspelling out any special safetymeasures required.

For this third and final issue in theseries dealing with wildland firebehavior, we chose articles frompast issues that reflect the variouselements involved in Barrows(1951) process of judging or pre-dicting wildland fire behavior.

Comparisons of FireBehavior Predictionsand Forecasts NeededAfter 50 years, the only item wewould add to Barrows (1951) out-line is the need for the fire behavioranalyst (FBAN) and others engagedin wildland fire management topause for a moment to compare, ina rigorous and systematic fashion,the FBANs or their own fire behav-

ior predictions to actual fire behav-ior. This is the only way one cantruly meet Barrows (1951) adviceto evaluate the combined effects ofall significant factors influencingfire behavior.

Conscious reflection, not as anafterthought but as a normal rou-tine in the day-to-day business offire behavior forecasting, involves ahighly professional method of ques-tioning whether our fire behavioraids, guides, and protocols areworking. By systematically reflect-ing upon our fire behavior forecastsand the tools that helped us pre-pare them, we become the mastersof fire behavior models and nottheir servants.

To paraphrase Dr. Karl Weick(2003)coauthor of Managing theUnexpected: Assuring HighPerformance in an Age ofComplexity (Weick and Sutcliffe2001)*becoming a mindful FBANis a constant struggle for alertness,and to be alert means to constant-ly and diligently seek instanceswhere your model didnt work andidentify indicators you missed thatsignaled expectations werent beingfilled.

We recommend that FBANs andothers adopt the framework of theAfter Action Review, as described onthe Wildland Fire Lessons LearnedCenter Website (),

by putting their fire behavior fore-casts through a reflective scrutinybased on four basic questions:

1. What did your fire behavior fore-cast say would happen?

2. What actually happened?3. Why did the fire behavior aid,

guide, or protocol predict accu-rately (or inaccurately)?

4. Finally (and most importantly),if you had to make this forecastagain, what would you do differ-ently? How would you changethe way you used the aid, guide,protocol, or model/system in thisdifferent approach?

Judging the quality of a fire behav-ior prediction or forecast solely onthe outcome can be hazardous. Bychance, good predictions or fore-casts can sometimes have bad out-comes and bad predictions or fore-casts can result in good outcomes(fig. 2). From a practical stand-point, overpredictions can be easilyreadjusted without serious, lastingconsequences, whereas underpre-dictions can be disastrous (table 1)from the standpoint of human safe-ty (i.e., for the public and for fire-

Figure 2The 2-by-2 fire behavior predic-tion or forecast matrix (based on Savelandand Wade 1991) shows that even good fore-casts can have unlucky outcomes.

* See D. Iverson, Book Review: Managing theUnexpected (Fire Management Today 62(4) [Fall 2002]:3637); and J. Williams, Next Steps in Wildland FireManagement (Fire Management Today 62(4) [Fall2002]: 3135).

OutcomeGood Bad

Objective Unlucky

Lucky Deserving

Good

BadFor

ecas

t


Although forestry dates backhundreds of years, organized for-est fire research has been under-way less than 30 years. Duringmuch of this time the majorefforts have been devoted to stud-ies of fire behavior or closelyallied fields. As a result, muchhas been learned about how firesact, in spite of the relatively shortperiod of organized effort.Knowledge stemming from anyresearch projects, plus the experi-ence gained from the control ofthousands of fires, provide a goodfoundation for a general under-standing of the complex subject.

The main purpose of this publica-tion is to summarize the mostimportant aspects of fire behavioras we now know them. Theauthor recognizes that there arestill many unknowns in thebehavior of forest and range fires.These unknowns will be the tar-gets of future research. In themeantime it is important that thebest available information on firebehavior be placed in the handsof the men who must carry onthe vital task of fire control

Knowledge of fire behavior is anessential requirement for fire-fighters. Successful fire controloperations depend, first of all,upon the ability of the protection

On the Place of Fire Behavior inWildland Fire Management*

*From Barrows (1951) handbook Fire Behavior inNorthern Rocky Mountain Forests.

forces to judge where and whenfires will start and how they willbehave once ignition takes place.Every member of the firefightingteam from ranger to smokechasermust be able to make reliable esti-mates of the behavior of fires burn-ing under a wide variety of condi-tions. These estimates must begood enough to provide the basisfor decisions which will lead to fast,efficient, and safe firefighting.

Fire Behavior andSuppression MethodsThe character and difficulty of thesuppression job on every firedepends largely upon the behaviorof the fire. The speed, strength, andtype of attack are governed by thelocation of the fire and its reactionto the surrounding environment.Each change in environment maychange fire behavior and in turncall for some adjustment in fire-fighting strategy and techniques.The ability of the man handling thesuppression job to evaluate thebehavior pattern largely determinesthe efficiency and economy of theentire firefighting operation.

A primary purpose of evaluating thebehavior of every fire is to reduceor prevent unexpected blowupsand runs. A careful check oneverything that will affect thebehavior of a fire reduces thechances for the unexpected.When a skilled size-up has been

made in advance, the unexpectedmay become expected and a poten-tial blow or run may often be antic-ipated soon enough to be prevent-ed. Effective fire control requiresthat suppression plans and actionbe carried out in accordance withcontinuing estimates and forecastsof what the fire is going to do.Analysis of fire behavior is a basicrequirement in firefighting applica-ble equally to the one-man smoke-chaser or the big fire where hun-dreds of men are in action.

Fire Behavior andSafetyAn important reason for under-standing fire behavior is to providesafety for the firefighters. Every firebehavior situation calls for specificsafety measures. Experience gainedfrom fighting thousands of fires hasshown that the suppression jobmay be accomplished with a rea-sonable degree of safety. To achievesafety it is highly important that allfirefighters have a general knowl-edge and the leaders of the fire-fighting forces have a high degreeof knowledge of fire behavior.

The most dangerous individual in asuppression organization is usuallythe man who is afraid of fire. Fear islargely a result of ignorance. Manyrisks can be eliminated from fire-fighting if each man knows what toexpect the fire to do. The averagefirefighter need not be an expert on


all phases of fire behavior, but heshould have a working knowledge ofignition, combustion, and rate ofspread of fires burning in forestfuels. Equipped with such basic firebehavior know-how the individualfirefighter can approach his jobwithout fear and with confidencethat he can perform required dutiesin a safe and efficient manner.

Fire Behavior and theForest ManagerIn the northern Rocky Mountainsfires influence many phases of theforest management job. The behav-ior of fires is an important factor inthe growth, harvesting, and regen-eration of forest crops. How oftenfires occur and how hot they burnaffect both the quality and quantityof products harvested from the for-est. The forest manager may influ-ence fire behavior by the nature ofhis operations, especially in timbercutting. When a forest is opened upby thinning or harvesting opera-tions, lower humidities, high tem-peratures, and higher wind veloci-ties are created within the stands.Fire behavior is thereby affected.Sometimes the debris remainingafter logging constitutes a fuel con-dition which greatly increases thechance for fires to ignite and burnintensely. For these reasons it isimportant for forest managers toknow fire behavior and to be able toevaluate the influence of forestmanagement operations on it.

Judging Fire BehaviorMany complex factors influence theignition, rate of spread, and generalbehavior of fires. Some of these fac-tors can be measured more or lessprecisely with instruments. Othersdo not lend themselves to exactmeasurements and therefore mustbe evaluated in general terms. Thecombined effects of all factors,whether measured precisely or not,determine the behavior of a fire. Nosingle factor, such as wind, steep-ness of slope, or kind of fuel, willprovide the answer to questions ofwhen and where fires will start andhow fast they will spread. Likewise,no single instrument or meter willanswer these fundamental ques-tions. Therefore it is necessary forthe fire control man to develop asystem aided by instruments andother guides where available, whichwill help him evaluate the com-bined effects of all significant fac-tors influencing fire behavior.

Keen observation is a fundamentalrequirement for judging fire behav-ior. Many visible signs are presentin the forest to assist the fire con-trol man in arriving at reliabledecisions. These include suchthings as the color of the grass andother annual vegetation, the posi-tion of a fire on a slope, the time ofday, and the amount of sunshinefiltering through the forest canopy.One of the purposes of this hand-book is to analyze the importance

and the meaning of the most sig-nificant of the many factors thatmay be observed and to present amethod of evaluating their com-bined effects.

Fire Safety MeasuresA thorough understanding of firebehavior is essential to the pro-motion of safety in firefightingoperations. Accidents often occurwhen so-called unexpected firebehavior develops. To avoidthese unexpected events, thefirst and most important safetymeasure on every fire, regardlessof size, is to make the estimate ofthe fire behavior situation.Fires behave according to certainlaws. Runaway fires do not justhappen. When keen observationsand evaluations are made ofweather, topography, and fuels,there are very slim chances forfirefighters to be surprised sud-denly by an unexpected blowup.

Every fire behavior situation callsfor special safety measures. Inmost cases the best safety meas-ure is aggressive and intelligentfirefighting aimed at abating thedanger spot.

Keen observation and interpreta-tion of weather, topography, andfuels lead to a good understand-ing of fire behavior and to safe,efficient firefighting.


fighters). Underpredictions can alsorender chosen operational strategyand tactics useless (Cheney 1981).

In addition to evaluating the out-come of a forecast, it is wise to lookat the fire behavior predictionprocess itself. Russo andSchoemaker (1989) examine com-mon pitfalls for decisionmakersthat are equally valid for FBANsand others making fire behaviorpredictions or forecasts. Decisiontrap 10 (see the sidebar) is a failureto audit the decisionmakingprocessa failure to understandthat ones decisionmaking leavesone constantly open to the othernine decision traps.

Other Related Articlesand Information Its worth noting that Fire Man-agement Today and its predeces-sors have also published a variety ofother fire behavior and fire behav-ior-related articles in the past 67years (Bunton 2000a, 2000b). Many

are shown in the list of additionalreferences beginning on page 10.

Because copies of many of thesearticles are difficult to obtain, eventhrough library sources, they arebeing scanned and will be madeavailable through the World WideWeb. Many are now available fordownloading from the Fire Man-agement Today Website(). The same Website has anauthor index posted for volumes159 of Fire Management Todayand its predecessors.

AcknowledgmentsThe authors offer their sincerestheartfelt appreciation to HutchBrown, Madelyn Dillon, and CarolLoSapio, editors of Fire Manage-ment Today, for their significantcontributions to this special issue,and to April Baily, the journalsgeneral manager, for supportingthe concept of these special issueson wildland fire behavior. Their

dedication and outstanding editori-al abilities have brought life tomany of the articles contained inthis issue that have long been for-gotten.

ReferencesAlexander, M.E. 2000. Fire behavior as a

factor in forest and rural fire suppression.For. Res. Bull. 197, For. Rural Fire Sci.Techn. Ser. Rep. 5. Rotorua andWellington, NZ: Forest Research in assoc.with New Fire Service Commission andNational Rural Fire Authority.

Alexander, M.E.; Thomas, D.A. 2003a.Wildland fire behavior case studies andanalyses: Value, approaches, and practicaluses. Fire Management Today. 63(3): 48.

Alexander, M.E.; Thomas, D.A. 2003b.Wildland fire behavior case studies andanalyses: Other examples, methods,reporting standards, and some practicaladvice. Fire Management Today. 63(4):412.

Judging the quality of afire behavior prediction

or forecast solely on theoutcome can be

hazardous.

Table 1The scope of quantitative wildland fire behavior prediction (adapted from Rothermel 1974, 1980).

ResolutionFire

situation Intended use Timeframe Area

Relative usefulness/

value

Ease of prediction accuracy

Impact of inaccurate prediction

Possible

Potential

Actual

Training

Long-range planning(e.g., preparedness

system development)

Short-term planning(e.g., daily fireassessment)

Near real-time(e.g., automateddispatch, projectfires, escaped firesituation analysis)

Long-term Notapplicable

Yearly/seasonal

State/province/territory

Daily/weekly

Forest/district

Minutes tohours

Stand- orsite-specific

Moderate

Good

Very good

Excellent

Extremely tovery easy

Easy to moderately

Easy

Moderately difficult to

difficult

Very toextremely difficult

Minor or minimal

Significant

Serious

Critical


1. Plunging in: Beginning togather information and reachconclusions without first tak-ing a few minutes to thinkabout the crux of the issueyoure facing or to thinkthrough how you believe deci-sions like this one should bemade.

2. Frame blindness: Setting outto solve the wrong problembecause, with little thought,you have created a mentalframework for your decisionthat causes you to overlookthe best options or lose sightof important objectives.

3. Lack of frame control:Failing to consciously definethe problem in more waysthan one or being undulyinfluenced by the frames ofothers.

4. Overconfidence in your judg-ment: Failing to collect keyfactual information becauseyou are too sure of yourassumptions and opinions.

5. Shortsighted shortcuts:Relying inappropriately onrules of thumb, such asimplicitly trusting the mostreadily available informationor anchoring too much onconvenient facts.

The Ten Most DangerousDecision Traps*

* Based on Russo and Schoemaker (1989).

6. Shooting from the hip:Believing you can keepstraight in your head all theinformation youve discovered,and therefore winging itrather than following a sys-tematic procedure when mak-ing the final choice.

7. Group failure: Assuming thatwith many smart peopleinvolved, good choices willfollow automatically, andtherefore failing to managethe group decisionmakingprocess.

8. Fooling yourself about feed-back: Failing to interpret theevidence from past outcomesfor what it really says, eitherbecause you are protectingyour ego or because you aretricked by hindsight.

9. Not keeping track: Assumingthat experience will make itslessons available automatical-ly, and therefore failing tokeep systematic records totrack the results of your deci-sions and failing to analyzethese results in ways thatreveal their key lessons.

10.Failure to audit your decisionprocess: Failing to create anorganized approach to under-standing your own decision-making, so that you remainconstantly exposed to all theabove mistakes.

Barrows, J.S. 1951. Fire behavior in north-ern Rocky Mountain forests. Stn. Pap. No.29. Missoula, MT: USDA Forest Service,Northern Rocky Mountain Forest andRange Experiment Station.

Brown, H. 2002. Thirtymile Fire: Firebehavior and management response. FireManagement Today. 62(3): 2330.

Bunton, D.R. 2000a. Creating an index thatmirrors our past. Fire ManagementToday. 60(1): 2731.

Bunton, D.R. 2000b. Subject indexVolumes 3159. Fire Management Today.60(1): 3294.

Cheney, N.P. 1981. Fire behaviour. In Gill,A.M.; Groves, R.H.; Noble, I.R., eds. Fireand the Australian Biota. Canberra,Australia: Australian Academy ofSciences: 151175.

Cornwall, M. 2003. Dome Peak Fire:Witnessing the extreme. FireManagement Today. 63(1): 1618.

Rothermel, R.C. 1974. Concepts in firemodeling. Paper prepared for AdvancedFire Management Training Course,National Fire Training Center, 1974November 1122, Marana, AZ.

Rothermel, R.C. 1980. Fire behavior sys-tems for fire management. In: Martin,R.E. and others, eds. Proceedings of theSixth Conference on Fire and ForestMeteorology. Washington, DC: 5864.

Rothermel, R.C. 1983. How to predict thespread and intensity of forest and rangefires. Gen. Tech. Rep. INT143. Ogden,UT: USDA Forest Service, IntermountainForest and Range Experiment Station.

Russo, J.E.; Schoemaker, P.J.H. 1989.Decision traps: Ten barriers to brilliantdecision-making and how to overcomethem. New York, NY: Simon and SchusterIncorporated.

Saveland, J.M.; Wade, D.D. 1991. Fire man-agement ramifications of HurricaneHugo. In: Andrews, P.L.; Potts, D.F., eds.Proceedings of the 11th Conference onFire and Forest Meteorology; 1991 April1619; Missoula, MT. SAF Publ. 9104.Bethesda, MD: Society of AmericanForesters: 124131.

Weick, K.E. 2002. Human factors in firebehavior analysis: Reconstructing theDude Fire. Fire Management Today.62(4): 815.

Weick, K.E. 2003. Managing the unexpect-ed: A look at the big ideas. Paper present-ed at the Georgia Techs DuPree Collegeof Management and Leadership Center,Carter Presidential Center; 2003 March25; Atlanta, GA.

Weick, K.E.; Sutcliffe, K.M. 2001. Managingthe unexpected: Assuring high perform-ance in an age of complexity. SanFrancisco, CA: Jossey-Bass.

Russo and Schoemaker (1989) examine commonpitfalls for decisionmakers that are equally valid for

FBANs and others making fire behaviorpredictions or forecasts.


Fire Behavior Officer/FireBehavior Analyst

Bushey, C.L.; Mutch, R.W. 1990. Firebehavior service center for extremewildfire activity. Fire ManagementNotes. 51(4): 3442.

Chandler, C.C.; Countryman, C.M. 1959.Use of fire behavior specialists can payoff. Fire Control Notes. 20(4): 130132.

Countryman, C.M.; Chandler, C.C. 1963.The fire behavior team approach in firecontrol. Fire Control Notes. 24(3):5660.

Dell, J.D. 1966. The fire-behavior team inactionThe Coyote Fire. Fire ControlNotes. 27(1): 810, 15.

Knutson, K.K. 1962. The place of the firebehavior officer in the fire suppressionorganization. Fire Control Notes. 23:8182.

Weick, K.E. 2002. Human factors in firebehavior analysis: Reconstructing theDude Fire. Fire Management Today.62(4): 815.

Training Alexander, M.E. 2002. The staff ride

approach to wildland fire behavior andfirefighter safety awareness training: Acommentary. Fire Management Today.62(4): 2530.

Andrews, P.L.; Sackett, S.S. 1989. Fireobservation exercisesA valuable partof fire behavior training. FireManagement Notes. 50(1): 4952.

Carlton, D.W. 1991. Fire behavior train-ingA look at some upcomingchanges. Fire Management Notes.52(2): 1519.

Cochran, A.R. 1957. A training course infire safety and fire suppression tech-niques. Fire Control Notes. 18(1):3338.

Editor. 1958. Safe practices underblowup conditionsA training outlinefor the fire crew boss. Fire ControlNotes. 19(1): 37.

Euler, D.H. 1946. The sand box as a fire-control training tool. Fire ControlNotes. 7(1): 3739.

Giffen, C.A. 1956. Fire control practices:A training course. Fire Control Notes.17(3): 2629.

Keller, P. 2002. Whats a staff ride? FireManagement Today. 62(4): 67.

Keller, P. 2002. Walk back into tragedy: Aquantum leap forward. FireManagement Today. 62(4): 1621.

Additional References on Wildland Fire Behavior*

* Articles on or related to fire behavior from issues ofFire Management Today and its predecessors (FireControl Notes, Fire Management, and FireManagement Notes) from 1936 to 2003 that were notreprinted or referenced elsewhere in this three-partseries of special issues (Fire Management Today vol-umes 63[3], 63[4], and 64[1]).

Moore, W.R. 1959. Training in the ten stan-dard fire fighting orders. Fire ControlNotes. 20(2): 5860.

Mutch, R.W. 2002. Why dont we just leavethe fireline? Fire Management Today.62(4): 2224.

Thomas, D.; Cook, W. 2002. Dude Fire staffride. Fire Management Today 62(4): 45.

Thorburn, W.R.; MacMillan, A.; Alexander,M.E.; Nimchuk, N.; Frederick, K.W.; VanNest, T.A. 2003. Principles of FireBehavior: A CD-ROM-based interactivemultimedia training course. FireManagement Today. 63(2): 4344.

Research Alexander, M.E.; Andrews, P.L. 1989.

Wildland fire occurrence and behavioranalysis in the year 2000 and beyond.Fire Management Notes. 50(4): 3537.

Alexander, M.E.; De Groot, W.J.; Hirsch,K.G.; Lanoville, R.A. 1989. Use of postersfor interpreting fire behavior and dangerresearch. Fire Management Notes. 59(2):4144.

Alexander, M.E.; Maffey, M.E. 199293.Predicting fire behavior in Canadas aspenforests. Fire Management Notes.5354(1): 1013.

Alexander, M.E.; Yancik, R.F. 1977. Theeffect of precommercial thinning on firepotential in a lodgepole pine stand. FireManagement Notes. 38(3): 79, 20.

Banks, W.G.; Frayer, H.C. 1966. Rate of for-est fire spread and resistance to controlin the fuel types of the Eastern Region.Fire Control Notes. 27(2): 1013.

Barry, E.F. 1942. How about the esprit decorps. Fire Control Notes. 6(3):124125.**

Byram, G.M.; Martin, R.E. 1962. Fire whirlsin the laboratory. Fire Control Notes.23(1): 1317.

Countryman, C.M. 1956. Old-growth con-version also converts fire climate. FireControl Notes. 17(4): 1519.

Countryman, C.M. 1973. The fire environ-ment concept. Fire Management. 34(2):17.

Curry, J.R. 1936. Fire behavior studies onthe Shasta Experimental Forest. FireControl Notes. 1(1): 1213.

Davis, L.S.; Martin, R.E. 1961. Timetem-perature relationships of test head firesand backfires. Fire Control Notes. 22(1):2021.

Davis, W.S. 1949. The rate of spreadfueldensity relationship. Fire Control Notes.10(2): 89.

Gisborne, H.T. 1942. Review of problemsand accomplishments in fire control andfire research. Fire Control Notes. 6(2):4763.

Greenlee, D.; Greenlee, J. 2002. Changes infire hazard as a result of the CerroGrande Fire. Fire Management Today.62(1): 1521.

Jemison, G.M. 1939. Determination of therate of spread of fire in the SouthernAppalachians. Fire Control Notes. 3(1):47.

Johnson, V.J. 1982. The dilemma of flamelength and intensity. Fire ManagementNotes. 43(4): 37.

Luke, R.H.; McArthur, A.G. 1963. Firebehavior studies in Australia. FireControl Notes. 24(4): 8792.

Sackett, S.S.; DeCoste, J.H. 1967. A newmobile fire laboratory. Fire ControlNotes. 28(4): 79.

Stocks, B.J. 1977. Fire behavior research inOntario. Fire Management Notes. 38(2):911, 19.

Traylor, R.E. 1961. Correlation of weatherto fire spread in grass and brush fuels onthe Snake River plains in southern Idaho.Fire Control Notes. 22(4): 118119.

Computerized Aids and DecisionSupport Systems

Andrews, P.L. 1986. Methods for predictingfire behaviorYou do have a choice. FireManagement Notes. 47(2): 610.

Andrews, P.L.; Bevins, C.D. 1999. BEHAVEfire modeling system: Redesign andexpansion. Fire Management Notes.59(2): 1619.

Andrews, P.L.; Chase, C.H. 1990. Update ofthe BEHAVE fire behavior prediction sys-tem. Fire Management Notes. 51(1):2225.

Eubanks, R.L.; Bradshaw, R.L; Andrews, P.L.1986. Current status of BEHAVE system.Fire Management Notes. 47(2): 2931.

Finn, M. 2001. British Columbia ForestService adds new software for wildlandfirefighting. Fire Management Today.61(2): 4344.

Finney, M.A.; Andrews, P.L. 1999. FAR-SITEA program for fire growth simula-tion. Fire Management Notes. 59(2):1315.

Rothermel, R.C. 1983. BEHAVE and youcan predict fire behavior. FireManagement Notes. 44(4): 1115.

Scott, J.H. 1999. NEXUS: a system forassessing crown fire hazard. FireManagement Notes. 59(2): 2024.

Van Gelder, R.J. 1976. A fire potentialassessment model for brush and grassfuels. Fire Management Notes. 37(3):1416.

Hand-Held Computer Technology Bradshaw, R.L.; Dean, W.A. 1980. Adding

print capability to your TI59 fire behav-ior CROM. Fire Management Notes.41(4): 78.

**See C.F. Olsen, Analysis of the Honey Fire (FireManagement Today 63(3) [Summer 2003]: 2941).


Burgan, R.E.; Susott, R.A. 1986. HP71replaces TI59 for fire calculations in thefield. Fire Management Notes. 47(2):1113.

Burgan, R.E.; Susott, R.A. 1988. Correctingan error in the HP71B fire behaviorCROM. Fire Management Notes. 49(2):3132.

Cohen, J.D.; Burgan, R.E. 1979. Hand-heldcalculator for fire danger/fire behavior.Fire Management Notes. 40(1): 89.

Research Instrumentation Clark, B.; Steuter, A.A.; Britton, C.M. 1981.

An inexpensive anemometer frame. FireManagement Notes. 42(3): 1314.

Dibble, D.L. 1960. Fire climate survey trail-er. Fire Control Notes. 21(4): 116120.

Little, E.C. 1973. Costs $10Foolprooftimer measures rate of fire spread. FireManagement. 34(4): 1012.

McMahon, C.K.; Adkins, C.W.; Rodgers, S.L.1986. A video image analysis system formeasuring fire behavior. FireManagement Notes. 47(1): 1015.

Schaefer, V.J. 1959. Use of the 60-secondprint camera for stereophotography ofproject fires and related activities. FireControl Notes. 20: 8990.

Supporting Tools and Equipment Anderson, K. 2001. NIFC FIRE RAWS unit

survives burnover. Fire ManagementToday. 61(2): 3942.

Clark, B.; Roberts, F. 1982. A belt weatherkit accessory for measuring woody fuelmoisture. Fire Management Notes. 43(3):2526.

Dell, J.D.; Hull, M.K. 1966. A fire-behaviorteam field unit. Fire Control Notes. 27(3):67.

Division of Forest Fire Research,Intermountain Forest and RangeExperiment Station. 1959. Belt weatherkit. Fire Control Notes. 20(4): 122123.

Ellis, G.R. 1965. A combination pocketmeter for windspeed and duration. FireControl Notes. 26(2): 5.

Fischer, W.C. 1978. New portable weatherinstrument shelter performs well. FireManagement Notes. 39(3): 1518.

Maxwell, F.; McCutchan, M.; Roberts, C.F.1974. Automation of fire weather obser-vations. Fire Management. 35(3): 2225.

Palmer, T.Y.; Pace, G.D. 1974. Microwaveoven dries fuels fast. Fire Management.35(2): 2223.

Sackett, S.S. 1980. An instrument for rapid,accurate determination of fuel moisturecontent. Fire Management Notes. 41(2):1718.

Warren, J.R. 1980. Remote automaticweather stations (RAWS). FireManagement Notes. 41(2): 1516.

Warren, J.R. 1986. Very portable remote

automatic weather stations. FireManagement Notes. 47(4): 57.

Fuels and Fuel Sampling Altobellis, A.T.; Cooper, R.W. 1963. Moisture

content of gallberry and palmetto duringa dry period. Fire Control Notes. 24(1):10.

Blank, R.W.; Simard, A.J.; Eenigenburg, J.E.1985. A tester for measuring the mois-ture content of dead fine fuels. FireManagement Notes. 46(2): 812.

Bruce, D. 1951. Fuel weights on theOsceola National Forest. Fire ControlNotes. 12(3): 2023.

Buck, C.C. 1951. Flammability of chaparraldepends on how it grows. Fire ControlNotes. 12(4): 27.

Countryman, C.M. 1974. Moisture in livingfuels affects fire behavior. FireManagement. 35(2): 1014.

Dieterich, J.H. 1963. Litter fuels in red pineplantations. Fire Control Notes. 24(4):103106.

Miller, R.K.; Schwandt, D.L. 1979. Slashfuel weights in red pine plantations. FireManagement Notes. 40(1): 67.

Potts, D.F.; Ryan, K.C.; Loveless Jr., R.S.1984. A procedure for estimating duffdepth. Fire Management Notes. 45(2):1315.

Scott, J.H.; Reinhardt, E.D. 2002.Estimating canopy fuels in coniferforests. Fire Management Today. 62(4):4550.

Weise, D.R.; Saveland, J.M. 1996.Monitoring live fuel moistureA taskforce report. Fire Management Notes.56(3): 1314.

Guidelines and Decision AidsAlexander, M.E.; Stam, J.C. 2003. Safety

alert for wildland firefighters: Fuel condi-tions in spruce-beetle-killed forests ofAlaska. Fire Management Today. 63(2):25.

Anderson, H.E. 1984. Calculating fire sizeand perimeter growth. Fire ManagementNotes. 45(3): 2530.

Cargill, G.E. 1970. Table speeds fire spreadestimates. Fire Control Notes. 31(2):1516.

Greenlee, J.; Greenlee, D. 2003. Triggerpoints and the rules of disengagement.63(1): 1013.

Melton, M. 1989. The Keetch/ByramDrought Index: A guide to fire conditionsand suppression problems. FireManagement Notes. 50(4): 3034.

Melton, M. 1996. KeetchByram DroughtIndex revisited: Prescribed fire applica-tions. Fire Management Notes. 56(4):711.

Mitchell, J.A. 1936. Rule of thumb fordetermining rate of spread. Fire Control

Notes. 1(7): 395396.Pirsko, A.R. 1961. Alinement chart for

perimeter increase of fires. FireControl Notes. 22(1): 14.

Fire Weather and FireWeather Forecasting

Countryman, C.M. 1972. This humiditybusiness: What it is all about and howit is used in fire control. Fire ControlNotes. 33(2): 1011.

Cramer, O.P. 1950. Use your weatherrecords to interpret fire-weather fore-casts. Fire Control Notes. 11(4): 4143.

Cuoco, C.J. 199293. Prescribed burns?Share information with fire weatherforecasters and involve them in theplanning. Fire Management Notes.5354(3): 1013.

Fite, F.M. 1953. Fire weather forecasts.Fire Control Notes. 14(1): 1820.

Fujioka, F.M. 1997. High resolution fireweather models. Fire ManagementNotes. 57(2): 2225.

Graham, H.E. 1964. A portable fire-weather forecast unit for use on back-country fires. Fire Control Notes.25(3): 11.

LaMois, L.M. 1961. Weather and forestfires. Fire Control Notes. 22(1): 2224.

ODell, C.A.; Hammer, L.C. 1979. Fireweather meteorological support units.Fire Management Notes. 40(2): 35.

Potter, B.E. 1997. Making sense of fireweather. Fire Management Notes.57(2): 2627.

Rodney, E.A. 1964. Forest fires and fireweather conditions in the Asheville,N.C., fire weather districtSpring sea-son, 1963. Fire Control Notes. 25(3):79, 15.

Schroeder, M.J. 1950. The Hudson BayHigh and the spring fire season in theLake States. Fire Control Notes. 11(1):18.

Svorcek, A.J. 1965. 50 years of fire weath-er service. Fire Control Notes. 26(2):89.

Watkins, C.H. 1961. The Oregon statemobile fire weather unit. Fire ControlNotes. 22(3): 8992.

Long-Duration ProjectionsLukens, D.; Krebs, J. 1986. Long-term

fire behavior projections. FireManagement Notes. 47(4): 2223.

Mohr, F.; Both, B. 1986. ConfinementAsuppression response for the future?Fire Management Notes. 56(2): 1722.

Mohr, F.; Lukens, D.; Terry, D. 1987.Managing confinement suppressionresponse on the Middle Ridge andLittle Granite Fires, August 1986. FireManagement Notes. 48(3): 2325.


pot fires which started upwindfrom going forest fires havebeen reported by I.S. Stivers,

Forest Ranger for the New YorkConservation Department, whosedistrict covers eastern Long Island.They had been observed on a num-ber of occasions, and from a num-ber of different fires.

Suspecting at first that incendiarieswere setting fires behind him,Stivers sent patrols upwind fromgoing fires. The patrols found noincendiaries but they did find newfires starting. They, and he, alsoobserved that the smoke column,after rising high in the air, turnedand moved back in a directionopposite to the surface winds. Thespots were starting from emberswhich fell from this smoke column.

On other occasions, Stivers wrote,surface winds changed abruptly inmid-afternoon from a northerly orwesterly to a southerly or easterlydirection, carrying going fires in anunexpected direction and upsettingsuppression plans. A typical casewas a fire on Sunday, April 1, 1945,at 2:30 p. m., that started with anorthwest wind and began tospread to the southeast. Fifteenminutes later the wind shifted fastto the southwest and sent the fireover the Radio CorporationCommunications plant atRiverhead.

* The article is reprinted from Fire Control Notes 8(2/3)[Spring/Summer 1947]: 3033.

FOREST FIRES AND SEA BREEZES*G.L. Hayes

When this article was originally published,G. L. Hayes was a forester for the USDAForest Service, Southeastern ForestExperiment Station, Asheville, NC.

S

The conditions described and thelocation, on Long Island, indicatethat the type of local winds knownas sea breezes was responsible forboth the upwind spot fires and forthe rapid changes in direction ofthe surface wind. Much has beenlearned about sea breezes in recentyears that should be of very materi-al help in planning fire suppressionin such coastal areas as LongIsland. Obviously, fire suppressionis most difficult when rapid andunexpected changes in wind condi-tions occur. If the wind shifts canbe anticipated, defensive action canbe planned in advance.

There is an excellent discussion ofsea breezes in the June 1946 issueof the bulletin of the AmericanMeteorological Society under thetitle Theory and Observation ofLand and Sea Breezes, byRaymond Wexler. As many fire con-trol men in coastal areas may nothave access to the Bulletin, the fol-lowing digest of Mr. Wexlers articlehas been prepared. The land breezeis not mentioned as it occurs main-ly at night and is felt primarily overthe water.

Definition andCharacteristics of Sea Breezes A sea breeze is a local circulation inwhich the wind near the surfaceblows from the water onto the land

and returns at a higher elevationfrom land to water. During the day-light hours the air is heated moreover the land than over the water.This sets up a local pressure systemthat induces the warmer, lighterland air to rise and flow seawardand the colder, heavier air over thewater to settle and flow landward.

The sea breezes occur on warmdays near the shores of large bodiesof water. They are strongest andbest developed along the seacoastsbut occur also along the shores ofbays and large lakes. In the temper-ate zone the landward flowing windcurrent may be from 200 to 2,000feet (60600 m) thick and mayreach inland for 20 to 25 miles(3240 km). Above this is thereturn current. Under the sameconditions it may extend offshoreas far as 60 miles (97 km) over theocean. In hotter climates or incombination with topographicwinds the inland range is extended.The winds from lakes extend short-er distances.

Two distinct types of sea breezes arerecognized. The first type developswhen there is little or no gradientwind;** the second type developswhen there is a light offland gradi-ent wind. The first type develops as

** The gradient wind is the air movement caused by theprevailing pressure differences in the atmosphere. It isthe wind that is usually predicted in the WeatherBureau forecasts.

Coastal surface winds can change directionabruptly in mid-afternoon, carrying going fires in

an unexpected direction and upsetting suppressionplans.


a small circulation near the shoreearly in the day, soon after the airover the land has become warmerthan the air over the water. Withcontinued heating of the land, thecirculation extends progressivelyfarther landward and seaward andgrows stronger and deeper.

The second type, which is the morecommon in temperate latitudes,develops over the water and usuallycomes onto the land suddenly, laterin the day. The offland gradientwind holds the colder and heaviersea air back and heats it up untilthe force of the wind can no longerhold it. Then the sea air rushesashore where it is heated until itrises and joins the gradient windwhich is blowing out to sea over-head. The typical sea breeze circu-lation is then established.

The most dangerous part of the seabreeze circulation, from the firecontrol standpoint, is the front orsurface separating the landwardblowing sea air from the seawardflowing land air. The reasons are:

1. The winds blow in opposingdirections on either side of thefront and rise at the front.

2. The front moves. The rate of itsadvance is less than the velocityof the sea breeze behind it and itdecreases as it moves fartherinland. When a front movesacross a fire, the rear or a flanksuddenly becomes the head ofthe fire.

3. The winds along the front arethe strongest and gustiest part ofthe sea breeze circulation. Initialgusts of the sea breeze as strongas 34 miles per hour (55 km/h)have been recorded, whereas theaverage behind the front is onlyabout 11 miles per hour (18km/h).

After about a half hour from thetime the front has passed, thevelocity is usually very constant,with little gustiness. As the higherwinds are then flowing opposite tothe surface winds, the danger ofupwind spot fires is present.

Although the sea breeze blows fromwater to land, it does not alwaysblow perpendicular to the coastline. It tends to blow perpendicularat first then shift to the right as theday grows older. Thus, along theeast coast where the shore is direct-ly north and south it would tend tostart as an easterly wind, shifting tosoutherly. Along the west coast itwould tend to start as a westerlywind, shifting to northerly.

External FactorsInfluencing SeaBreezes Several conditions affect sea breezeformation and behavior.

1. Character of day. As sea breezesoccur only when the air over theland becomes warmer than overthe sea, clear, hot days are mostfavorable to their formation.They can and do occur on over-cast days but they form later, aremilder, and extend inland forshorter distances. In general, theclearer and hotter the day, theearlier the sea breeze will form,the stronger it will get, and thefarther inland it will penetrate.With light gradient winds andclear skies, it usually starts about2 to 3 hours after sunrise andends within 2 hours before sun-set.

2. Gradient wind. Calm conditions,or a light offland gradient windare favorable for sea breeze for-mation. If the gradient wind isblowing parallel to the shore oroff the water, the sea breeze willnot develop.

The velocity of the offland gradi-ent wind affects the time ofarrival of the sea breeze and thedistance inland that it will move.Under calm conditions, the seabreeze may develop near theshore soon after sunup and moveprogressively farther inland untilthe maximum temperature forthe day is reached, after which issubsides. The stronger theoffland gradient wind, the laterin the day the sea breeze comesashore, and it may never pene-trate far inland. In fact, if thewind is strong enough, the seaair cannot leave the water. AtDanzig a gradient wind of 22miles per hour (35 km/h) wasobserved just to balance theforce of the sea breeze. The frontmoved intermittently back andforth across the shore line.

To have a front stall over a firewould create a very bad situa-tion. The winds could be strong,and would certainly be gusty andfluctuate wildly in direction, asthe front moved back and forth.

3. Topography. Where there aremountains along a shore line,the sea breeze may combine withan upvalley or upslope wind.Such a combination wind isstronger than a straight sea

The most dangerous part of the sea breezecirculation is the front or surface separating the

landward blowing sea air from the seaward flowingland air.


Where the sea breeze is observed to haveimportant effects on fires, fire control men would

profit by observing its characteristics.

breeze and may extend much far-ther inland. If the mountains lieseveral miles back from thecoast, separate circulations maybe set up in the morning whichwill merge after noon. Such acombination in California isreported to establish a continu-ous flow of wind for as much as40 miles (64 km) inland. A simi-lar but less extensive flow takesplace between Great Salt Lakeand the Wasatch Mountains inUtah.

Along the shores of a bay theremay be two components of thesea breeze, one from the bay andthe second from the sea beyond.The bay circulation will usuallybe the first to affect the land butmay be replaced later by theocean breeze, accompanied by achange in wind direction.

4. Vegetation. A heavy vegetativecover retards heating of the landsurface. Hence, the sea breezestarts earlier and becomesstronger along desert or semi-desert coasts than along heavilyforested ones. Likewise, withother things equal, conditions

along our coast are more favor-able to sea breezes when the veg-etation is dead and the leaves areoff the deciduous trees than afterthe fields and woods green up.

5. Atmospheric stability. An unsta-ble lower atmosphere is morefavorable for sea breezes than astable one. In an unsaturatedatmosphere, stability depends onthe rate of temperature dropwith increasing elevation. If thetemperature decreases morethan 5-1/2 F in 1,000 feet of ele-vation (or 1 F in 182 feet), theair is unstable and ascendingconvection currents develop eas-ily. If it decreases less than this,it is stable and convectionalmovement cannot take place. Airover the land that is very stablein the morning may, throughsurface heating, become unstablelater in the day, hence thehottest part of the day is mostfavorable for sea breezes.

6. Distance from the shore. Thesea breeze is felt first and hasgreatest velocity right at theshore. As distance from shore isincreased the sea breeze arriveslater in the day, has less velocity,and the front moves more slowly.

With so many factors affecting thetime of arrival and characteristicsof the sea breeze, it is impossible toset up definite rules which will tellwhen it may arrive or how it willbehave for any particular place orday. Where the sea breeze isobserved to have important effectson fires, fire control men wouldprofit by observing its characteris-tics as related to the factors alreadydiscussed. Or the local weatherforecaster of the U.S. WeatherBureau might be induced to predictthe time of arrival, its range inland,and probable velocity at and behindthe front.

Russo and Schoemaker (1989) Decision Trap 1Plunging In:Beginning to gather information and reach conclusions without first taking a

few minutes to think about the crux of the issue youre facing or to thinkthrough how you believe decisions like this one should be made.*

* See page 9.


ur job of fire control can bedone, in fact has been done, inseveral ways: By brute strength

and little attention to the condi-tions we are attempting to control;by observation of what is happeningbut with little or no understandingof why the fire is behaving as itdoes; or by practical application ofknowledge of the basic laws ofchemistry and physics that areactually determining the rate atwhich a fire is spreading. Let uslook into the most significant fac-tors that affect fire behavior.

Fire is a ChemicalProcess Combustion is a chemical process.It is classified that way becausecombustion, with or without flame,is a molecular reaction in whichmolecules of oxygen in the air com-bine with molecules of celluloseand lignin (which make wood) andthereby change most of the solidinto gases. These gases are mole-cules of different substances. Theyare no longer cellulose and lignin.Such changes of substance arechemical, not physical, processes.When these changes occur at sucha rapid rate that heat and flame areproduced, the process is calledcombustion or fire.

When you look into the fundamen-tals of combustion and find that

There are only three things you can do to stop afirerob it of its fuel, keep it from being heated to

the ignition point, or shut off the oxygen supply.

* The article is reprinted from Fire Control Notes 9(1)[Winter 1948]: 1324. It was used at the 40-man FireBoss School on May 5, 1947.

When this article was originally published,H.T. Gisborne was in charge of the Divisionof Forest Protection for the USDA ForestService, Northern Rocky Mountain Forestand Range Experiment Station.

FUNDAMENTALS OF FIRE BEHAVIOR*H.T. Gisborne

Othere are only three basic factors orthree essentials to this chemicalprocess, it is obvious that we areoverlooking a bet if we fail to con-sider each of these three things inour calculating.

Three Essentials of Combustion.Completely controlling the chemi-cal reaction called fire are onlythree essentials. They are:

1. Fuel or something that will com-bine with oxygen rapidly enoughto generate heat;

2. Heat enough to raise that fuel tothe ignition point; and

3. Plenty of oxygen in contact withthe fuel or with the gases evolvedfrom the wood.

Remove the fuel as we do when wedig a fire trench; keep it from beingheated to the ignition point, as wedo when we widen the trench orwhen we use water; or shut off thesupply of oxygen as we do when wethrow dirt, use water, or bury aburning log, and you can stop thespread of any fire. Every one of ourmethods of fighting fire is based onone or more of those three simpleessentials. THERE ARE NO OTHERWAYS.

Fuel. Chemically, all of the fuelsthat carry our fires are practicallyalike. From grass and brush to treeneedles, tree trunks, and rottenwood on the ground, they are all ofthe type that the chemist desig-

nates as (C6H10O5)y. This means thatthere are 6 atoms of carbon, 10atoms of hydrogen, and 5 of oxygenin each molecule of cellulose.Starch, which is found in the roots,seeds, and leaves of all plants, isvery similar, differing only in thesubscript. The chemists designatethe various starches as (C6H10O5)x.

This point is important to remem-ber because it helps to reduce someerrors of judgment based on thebelief that the chemical nature ofour fuels differs very materially.When C6H10O5 burns, every mole-cule of that substance combineswith six molecules of oxygen. Theresultant products are gases, 6 mol-ecules of carbon dioxide, and 5molecules of water vapor. Firemakes water out of the hydrogenand oxygen atoms that are in everymolecule of wood. The chemistwrites it this way: C6H10O5 + 6O2 6CO2 + 5H2O. Unfortunately, thatwater is not of any help to usbecause it exists as a gas, a super-heated gas, which rises straight upand away from our fuels. The waterthat really counts is the moisturecontent of the grass, trees, or brushbefore they burn.

Because of this similarity of chemi-cal composition of our fuels, it isobvious that we should not calcu-late probabilities on the belief thatdifferent kinds of wood or brush orgrass burn differently. The leaves ofgrass, trees, and brush and the bark


Moderate to large areas of fuel releasing theirenergy suddenly are creating conditions that breed

not only higher wind velocities, but twisters oreven big whirlwinds.

and wood of trees are all largelycellulose. The big variable whichproduces really significant differ-ences in fire behavior is not thechemicals, it is the moisture con-tent.

There are, however, two otheringredients in wood in addition tocellulose that are of some, perhapsacademic, significance. One ofthese is lignin, a substance forwhich the chemists do not knowthe formula. The significance oflignin lies in the fact that it has aslightly higher heat content thancellulose and that it leaches anddecays more slowly. Hence oldwood is likely to have lost more cel-lulose than lignin and thereforewill have a slightly higher heat con-tent per pound of material remain-ing than fresh cut or freshly killedwood. Differences in the pitch con-tent are also known to affect theheat of a fire.

There are also some other minordifferences in the chemical natureof plant and tree leaves, but a seriesof tests of the fat and oil content ofthe leaves of six different genera ofweeds and brush which were madefor three consecutive summersfailed to reveal anything significant.Instead, this chemical study madeat our Priest River laboratory con-firmed the finding that moisturecontent is THE big variable.

Ignition. When there is plenty offuel, the next essential of combus-tion is that it must be heated to theignition point. For dry cellulose, atemperature of only 400 F to 600F (204316 C) is required. Theaverage usually used is 540 F (282 C). The point that is of practi-cal importance is that if your fuelsare even moderately dry they donot have to be heated very hot toreach this ignition temperature. In

other words the kindling tempera-ture of grass, wood, cotton batten,or cellulose in any natural form iseasily produced. It is not an abnor-mally high temperature. You willbuild more held line and have tocharge up less line lost if youremember that simple fact andthen do something about it.

The key to ignition is the ease withwhich a fuel can be heated to 540F (282 C). That ease naturallydepends upon one obvious differ-ence in fuels, i.e., their size. Thefine fuel naturally heats clearthrough and reaches 540 F (282C) far quicker than a heavy fuellike a log. Size of fuel is thereforethe significant feature to watch,other things such as moisture con-tent being equal. Actually, size andmoisture content influence theprocess of combustion in much thesame way. Make a stick wetter andyou reduce its ease of ignition.Similarly, the bigger the stick, theharder it is to ignite it. The wetstick and the big stick both requiremore time or more heat to raisetheir surface temperature to theignition point. And that is anothergood basic fact to keep in mindboth in sizing up probable firebehavior and in deciding on tacticsto use along the line. Let your fireburn through the heavier fuelswhere it will burn more slowly.Fight it at those places where itwould go into finer fuels and spreadfaster. Also, fire line construction iseasier in the fine fuels. You gain intwo ways by using this basic knowl-edge.

Size of fuel is also worth notingfrom another angle. Take 10pounds (4.5 kg) of dry grass or deadpine needles, 10 pounds (4.5 kg) ofdry branchwood, and 10 pounds(4.5 kg) of log in one chunk andignite each of them. What happens?The needles will liberate theirB.t.u.s (British thermal units) in afew seconds, the branches willrelease theirs in a few minutes,while the 10-pound (4.5-kg) logmay take half an hour to release itsheat. Ease of ignition is, therefore,not the only difference in firebehavior to expect in accordancewith different sizes of fuel. The rateof release of the energy is alsotremendously different.

This feature, combustion rate, iswhat a football player would callthe triple threat of fire. And thisrate of release of energy is the onefeature we fail most often to recog-nize. The three threats involvedare:

1. The more sudden the release ofall this heat, the farther it willradiate a temperature of morethan 540 F (282 C). And thatmeans something to your tactics.It means that if the fuels areeven moderately dry, a wider fireline is needed wherever you findan appreciable volume of finefuels. This applies to both stop-ping a fire and in backfiring.

2. The faster the release of thoseB.t.u.s, the greater the volumeof gas suddenly created, hencethe faster it will rise overhead.That also means something totactics employed, because theswifter the rise of hot air the


The most important variable in fire behavior is fuelmoisture, and when our fuel moisture indicatorsticks are below 5 percent you can expect your

fires to blow up and explode.

greater the chance of sucking upblazing embers and carryingthem up and over the line, if thesmoke is leaning across the line.That means spot fires.

3. The faster this release of energyand the faster the uprush createdby it, the greater the local windvelocity created by the fire.Moderate to large areas of fuelreleasing their energy suddenlyare creating conditions thatbreed not only higher windvelocities, but twisters or evenbig whirlwinds. I once saw one ofthe really big ones whirl like atremendous barrel and moveacross 2 square miles (5.2 km2)while I was running 200 yards(180 m) along the top of DesertMountain, on the FlatheadForest.

Oxygen. This last essential of com-bustion is one that we cant do verymuch about. Combustion engineerswho design and operate boilers do alot by controlling this one of thethree essentials. But under ourconditions there is a1most alwaysplenty of oxygen to facilitate com-bustion of our fuels. Under freeburning conditions such as occuron a forest fire, about 10 pounds(4.5 kg) or 133 cubic feet (3.75 m

3)

of air is needed for the completecombustion of only 1 pound (0.45kg) of dry fuel.

The one time when we do some-thing to reduce the oxygen supplyis in throwing dirt. While that dirtdoes lower the temperature of thefuel it lands on, the principal func-tion of dirt is to shut off or at leastreduce the supply of oxygen. Moist

dirt is superior to dry dirt primarilybecause it lowers the temperaturemore. But when either moist or drysoil covers the surface of the fuelthe major benefit is by cuttingdown the oxygen supply. Water alsodoes the same thing if enough isapplied to form a film over the sur-face of the fuel. But here too themajor benefit is in lowering thefuel temperature below the ignitionpint.

CombustionA Molecular ChainReaction. The public has heardand read a lot recently about atom-ic fission, so controlled that itbecomes a chain reaction andthereby makes possible atomicbombs. More understanding of thefire job and better financial supportby the public may follow when weshow that the job of fire control isdefinitely one of stopping a chainreaction which differs from thebombs primarily in that ours is amolecular instead of an atomicchain reaction.

A chain reaction may be comparedto a chain letter; you receive onebut you send out two or maybethree or four. Each of the recipientsof one of these letters similarlysends out two or three or four. Thething spreads like wildfire. The firstproblem in producing an atomicbomb was along this line. Thatproblem was to obtain certainchemicals which, when assembledin a sufficient quantity andarrangement, known as the criticalmass, would perpetuate theprocess of splitting atoms of urani-um into atoms of two other ele-ments, barium and krypton. It was

known as far back as 1939 that inthis splitting tremendous energywas released and that the processthen split other uranium atomswhich in turn released more energyand split more atoms, the processcontinuing and accelerating as longas there was a supply of a suitablefuel in a proper arrangement andcondition.. The job of the atomicphysicists was, therefore, to pro-duce this chain reaction yet controlit. Our job is simpler. It is merely tocontrol the molecular chain reac-tion that is fire.

As you can see, fire is a similarprocess in that if you heat one mol-ecule of a fuel to the ignition point,its process of changing fromC6H10O5 into CO2 and H2O mayrelease enough energy to igniteseveral other adjacent molecules ofC6H10O5. If the fuel is in a criticalcondition (dry enough), as com-pared to a critical mass (largeenough), that process thenbecomes a chain reaction and notonly spreads like wildfire but itreally is wildfire in our case.Whereas the nuclear physicistshave to make their fuels, andarrange them carefully in an atom-ic pile, our fuels are arranged for usand then, periodically, are put intoproper condition (dryness) suchthat the chain reaction starts when-ever and wherever the spark isapplied.

If this sounds farfetched or academ-ic, let me call your attention to onemore fact, which I know you willnot dispute. It is this: That whenour fuels are in their most criticalcondition, i.e., their driest, we havesome molecular chain reactionswhich are so violent that we cannotstop them, just as there is no stop-ping an atomic bomb once its chainreaction is started. Furthermore,we have occasions when combus-tion in the form of a forest fire


approaches a rate and even a mag-nitude rivaling an atomic bomb.Those of you who were on any ofour big fires in 1929, 1931, and1934 probably saw some of theseexplosions. Many of them coveredseveral square miles in only aminute or two.

If you will keep this chain reactionidea in mind, and if you will size upyour fire, either as a whole or onyour sector, in the light of the threebasic essentials of combustion, youmay be able to calculate the proba-bility of one of these explosions. Ifyou can do that, you may be able tosave your own life and the lives ofyour men, as well as improve yourfire control tactics.

There is one basic criterion towatch, however, in trying to antici-pate a molecular chain reaction atan explosive rate. This is moisturecontent of the fuel, for it is mois-ture content, not mass, nor vol-ume, nor size, nor arrangement offuel which first determines whetheror not a forest fire can trulyexplode. And you should rememberthat this moisture content not onlycan be, but is being measured. Youcan get these measurements everyday if you want them.

Moisture ContentThe Critical Variable We have not had any true forest fireexplosions in Region 1 since 1936. Ibelieve there were a couple ofminor ones that year on the LittleRockies Fire on the Lewis andClark Forest. But we had severalreally big ones in 1934, 1931, 1929,and one or two in 1926. You haveall read about those in 1919 and1910. The main reason why wehave not had any explosions inrecent years is this matter of mois-ture content. Our fuels simply havenot dried out to the critical condi-

tion that developed in those earliercritical years. Hence, it is evidentthat the critical variable in firebehavior is moisture content of thefuels. Consequently, I want to callyour attention to some of the possi-bilities available to you for improv-ing your calculation of probabilitiesby watching fuel moisture above allother elements.

Basis of Fuel MoistureMeasurements. You all know aboutthe fuel moisture indicator sticksused at some 175 fire danger sta-tions in Region 1. There are somethings those sticks will tell you far

protest, we discontinued used ofthe 2-inch (5-cm) ones. Finally, in1942, with the Model 6 DangerMeter, we dropped duff moistureand began to rely solely on the half-inch (13-mm) sticks.

From a technical viewpoint thesehalf-inch (13-mm) sticks alone failto represent our fuels in two ways:

1. They do not show the true bene-fits of light rains as well as duffmoisture measurements did; and

2. After heavy rains, they dry outfaster than either duff or 2-inch-diameter (5-cm) sticks.

The error is therefore alwaystoward showing more danger thanwould be revealed if all of the sig-nificant forest fuels were measured.The half-inch (13-mm) sticks arenot too fast, of course, for cheat-grass, but this fuel type does notcover a large percentage of ourarea. Furthermore, after it hascured, cheatgrass responds soclosely to changes of relativehumidity that humidity measure-ments can very well be used as anindex of moisture content of thatone fuel type. Finally, cheatgrasschanges moisture and flammabilityso rapidly that you might as wellalways be ready for the worst.

The half-inch (13-mm) sticks whichwe now use are made from newlumber each year. Any one of sever-al species of wood could be used,because here again we are dealingprimarily with cellulose. We useponderosa pine because it is readilyobtainable in clear stock at a rea-sonable price. We use only sapwoodbecause it is the moisture contentof sapwood of twigs, branches, logs,and snags in which we are mostinterested. We can ignore the mois-ture content of the heartwood of alog because if the outer sapwood is

better, far more accurately than youcan estimate. To make best use ofthose stick measurements you needto know: Why we use half-inch (13-mm) sticks, how they are made,and how accurate they are.

For four consecutive summers,1922, 1923, 1924, and 1925, I col-lected at periodic intervals samplesof the five major dead fuels thatburn in a forest fire. I took thesesamples to the laboratory anddetermined their moisture con-tents. I found out which fluctuatedthe most, and which the least. Onthis basis, I selected the top layer ofduff, half-inch (13-mm) sticks, and2-inch-diameter (5-cm) branchwood as the best representations.We therefore used duff hygrome-ters, half-inch (13-mm) sticks, and2-inch (5-cm) sticks at several firedanger stations for the next 5 yearsto measure fuel moisture. Then, atthe suggestion of the rangers in aregional meeting and despite my

A burning index rating isessential to calculationof the probabilities in

any fuel type.


extremely dry the inner heartwoodhas got to be dry too. We alsoignore the effect that bark has onnatural wood, because if we usednatural sticks with bark on themsome of that bark would soon chipoff and then we would no longerknow the true oven-dry weight ofour sticks.

To be sure that moisture measure-ments made at different stations donot differ because of differencesbetween the sticks or because oferrors by the danger station opera-tor, we go to a lot of work andincur considerable expense. Thesesticks now cost from $1 to $1.75per set to manufacture. In makingthem they are oven-dried and thencut off at the ends until they weighexactly 100.0 grams oven dry. Thisis done so that all that is needed todetermine their moisture contentin percent is to weigh them andsubtract 100.0 from the totalweight.

As you can see, this difference inweight is not only the weight of thewater in the wood, picked up fromthe air and from rain, but it is alsothe moisture content expressed as apercentage of the oven-dry weight.Consequently, when you call for afuel moisture content measure-ment from any of our stations youcan bank on its accuracy probably95 times out of 100. The other 5times the scales will be out of bal-ance, which is an operator error, orthe operator will have read thescales wrong. Eliminating thaterror is a job for training andsupervision.

Application of Stick Moisture. Bythe present practice we measurestick moistures at only two to fouroccupied stations per ranger dis-trict. That is not enough undersome conditions of spotted weather,

wet here and dry there, but underwidespread and long continueddrought it is fully adequate. Thesticks are exposed on a flat, in theopen, but under a shading layer ofscreen cloth. The reason for this,preparing to meet average-badconditions, is used in all fire con-trol planning in Region 1. Thesticks are therefore always exposedalike at all stations so that theresults are truly comparable.

The intention in such an exposureis to sample average-bad but notthe very worst conditions. By sam-pling average-bad conditions we areusing the sound engineering prin-ciple of preparing for the worstprobable but not the worst possible.Engineers did not build the GoldenGate Bridge at San Francisco towithstand the worst possible earth-quake. They built it to withstandthe worst probable. Few ditches,storm sewers, or bridges are builtto withstand the worst possibleflood. To meet worst possible condi-tions usually costs more than theresource is worth. It is better eco-nomics therefore to accept the riskof the worst possible flood, earth-quake, or fire weather conditions,and plan to meet only the average-bad or worst probable. We can getadequate fire control at a justifiablecost by using this principle. We douse it, not only in fire danger meas-urement, but also in all phases offire control planning in Region 1.

The double layer of 12-mesh screencloth under which we expose oursticks provides an amount of shadeand a fuel-moisture equivalent towhat you would get if you operatedtwo danger stations, one in full sun

and one under the half shade leftafter a moderately heavy loggingoperation. The stick moisturesobtained by this method can there-fore be accepted as representingaverage-bad conditions. Open southslopes will have drier half-inchsticks. Densely timbered northslopes will have materially higherfuel moistures. But when the sticksat our stations have high moisturecontents, adjacent areas, both openand timbered, also can be expectedto be moist to wet. When our sticksare each day showing lower andlower moistures you can depend onit that both the open areas and thetimbered slopes will also be gettingdrier and drier.

Our present sticks and exposurestherefore give you one definite anddependable index to watch. Theygive you something that you canuse in calculating, instead of guess-ing.

The most significant single featureof stick moistures to watch for isjust this: Are they below 5 percentand how long have they been there?Your danger of blow-ups and explo-sions can be really calculated bygetting merely that information. Ifthe sticks at both the nearestranger station and some nearbylookout have been down below 5percent for several days you canbank on it that every fuel type inthat area is in a truly critical condi-tion. Fortunately, this does nothappen very often, but it has hap-pened and it will happen again.When it does you will be makingthe mistake of your life if you fail toknow it. You can always find out byconsulting the local ranger station

Within the mid-elevation thermal belt, you canexpect the least benefit from increased fuel

moisture at night.


fire danger charts or Form 120 R-1.If you are already out on a fire aphone call will bring you thedesired information.

If the sticks are reported as at lessthan 5 percent, you should then askfor two more things: a check of thecomputations to be sure no errorswere made, and a remeasurementof the sticks right then. The dis-patcher or his assistant can do bothof these in 10 or 15 minutes. Ifthese checks verify the originalreports, you can then calculate thatevery fuel type in the area, on bothnorth and south slopes, and at allaltitudes, is in its most explosivecondition. You can bank on it thatfire will spread in all of these typesat the fastest rate, that there will belittle difference in rate of spreadbetween fuel types, and that thedanger of both spotting and of bigwhirls will be at a maximum. Youcan expect a chain reaction at itsworst.

Those of you who have never seenfires like the Lost Johnny and HalfMoon on the Flathead in 1929, theFreeman Lake on the Kaniksu andthe McPherson on the CoeurdAlene in 1931, and the Pete Kingon the Selway in 1934, simply can-not fully appreciate the significanceand the danger under these condi-tions. It may be enough to pointout that the Freeman Lake Fire,starting at 10:30 a.m. on August 3,1931, exploded almost from thestart to cover 20,000 acres (8,100ha) in the next 12-1/2 hours. This isat the rate of 1,600 acres per hour(650 ha/h), from a standing start!Both duff and 2-inch-diameter (5-cm) sticks were down to 4 percentmoisture content that afternoon.Wind was 13 miles per hour (21km/h) at 10 a. m., and 18 miles perhour (29 km/h) at 7 to 8 p.m.Relative humidity was 10 percent

or lower from 2 till after 7 p.m.THAT is explosive fire weather.

Differences in rate of spreadbetween fuel types practically disap-pear under these explosive condi-tions. The basic laws of chemistrytake charge when nature producessuch conditions, and the molecularchain reaction is actually unstop-pable until the wind goes down, thehumidity goes up, and the fuelsabsorb a little moisture. If you haveto fight such fires, and you shouldbe mentally ready for it, you willprobably do it like Kelley and Ryanfought the Freeman Lake explosion.You will not build much fire linethat day, but you will calculatewhere that fire front will be at mid-night and you will then have firecamps and men well distributedaround it and ready to begin workat the first crack of dawn. Kelleyand Ryan had more than 600 menstrung around the Freeman LakeFire front the next morning afterthat fire started, and those mennever let that fire make anothermajor run. That is a record to shootfor; it has seldom if ever beenequaled in this region.

The real difficulties and the mostfrequent need of skill and under-standing by fire bosses come, how-ever, in judging gradations betweenthis explosive condition and thateasiest of all conditions, when firewill spread, but only so slowly thatcontrol is largely a problem of howto do it at the least cost. In betweenthis explosive condition and theeasiest condition, other factors thanstick moisture become more andmore important and all the factors

become much more involved. Itshould be evident, nevertheless,that fuel moisture is THE majorvariable and that if you are to cal-culate accurately, your first andbest bet is to get the stick mois-tures and other measurementsfrom the nearest danger stationsbefore you even start to order men.After you get to the fire, you canthen see to it that you are informedeach day, preferably twice a day, asto how fuel moisture and other fac-tors are changing. There are thenthree other major variables towatch. These are fuel type, thethermal belt, and wind.

Fuel Types Some men have a misconceptionabout fuel types because they donot understand that our four ratesof spreadExtreme, High,Medium, and Lowrepresent dif-ferences only on a class 65 to class75 day. Obviously, rate of spreadwill not differ at all in differenttypes when the woods are soakingwet. Also, rate of spread is verynearly the same in all types afterseveral August days with the tem-perature at 100 F (38 C), humidi-ty at 10 or 15 percent, and theafternoon wind at 15 to 20 milesper hour (2432 km/h). Hence, wehave used the principle of prepar-ing for the average-bad in our fueltype classification, and the ratesgiven on our fuel type maps arethose to be expected on an average-bad day. This is about class 70 onour burning index meter. You can-not use those fuel type maps cor-rectly, or dependably, on any otherbasis.

Although fuel moisture is the critical variable formaking fuels explosive, wind velocity is often the

straw that breaks the camels back.


Our fuel type classes are thereforebased on differences in rate ofspread, not at the explosive pointwhere we can do nothing about it,but at combinations of moisturecontents, wind velocity, and vegeta-tive conditions just short of theexplosive point. These begin earlyin August whenever fuel moisturedrops to 5 or 6 percent, the humid-ity falls to less than 15 or 20 per-cent, and the wind rises above itsnormal afternoon average of 6 or 8miles per hour (1013 km/h). Afterseveral days of such weather, espe-cially if the burning index rises to75, as it will with fuels under 5 per-cent, humidity under 10 percent,and winds of more than 10 milesper hour (16 km/h), differences inrate of spread become less and lessas all fuel types approach the explo-sive condition.

A burning index rating is thereforeessential to calculation of the prob-abilities in any fuel type. If it showsclass 65 to 75, you can count onthe differences shown by the fueltype map, insofar as that map iswell made. The weaknesses in thesemaps are well recognized and stepsare being taken to correct them.

In applying the burning index to acorrect fuel type map, some guideshave been worked out, but this isunfortunately a field in which ourfire research has been woefullyweak. Our best contribution is inU.S.D.A. Circular 591, Influences ofAltitude and Aspect on DailyVariations in Factors of FireDanger, by Lloyd Hayes, publishedin 1941. The outstanding new factresulting from this research wasthe discovery and general locationof what Hayes called the thermalbelt.

Thermal BeltThe major significance of this ther-mal belt is that inside a certain alti-tudinal zone burning conditionschange less from daytime to night-time than they do in either the val-ley bottoms or on the mountaintops. At Priest River this zonebegins about 600 feet (180 m)above the valley bottom and contin-ues upward for about 1,000 feet(300 m). Below and above this zonefuels pick up more moisture atnight than they do within it. Withinthe zone the fuels lose a little everyafternoon and pick up a few percentbetween 6 p.m. and 3 a.m., but thechange is very slight. Up on themountain top, however, the samefuels will pick up 4 percent more atnight and lose 4 percent more inthe daytime. Down in the valleybottom they will pick up and lose 8to 12 percent more than within thethermal belt. This is true on bothnorth and south aspects. The onlyplaces where it may not hold trueare in steep-sided, deep, east andwest canyons like that of theSalmon River. In that canyon andperhaps in a few other spots like it,the depth of the canyon and its ori-entation in relation to prevailingwinds combine to interfere withnormal air drainage. There thethermal belt effect becomes lesspronounced or even disappears.Sometimes going fires will also dis-rupt this belt, if the fires are largeenough, but in most places andunder most conditions you shouldcalculate your probabilities on thebasis of the known difference ofburning conditions within thisthermal belt.

The next time you have a fire start-ing in late afternoon or earlyevening about 1,000 feet (300 m)up from the main valley bottom, Isuggest that you note for your-selves whether or not that particu-lar fire does not run faster and formore hours during the night than asimilar fire in the valley bottom.Also note whether or not that firepicks up and starts to run earlier inthe morning. I think you will findboth of these conditions in almostall thermal belt fires. They areessential elements in the equationrequired to calculate the probabili-ties.

These facts also should be highlysignificant to all fire dispatchers.Other things being equal, moremen should be sent, and theyshould be speeded on their wayfaster to every fire in the thermalbelt. Furthermore, on a going fire,if night work can be done on anysector, it should be planned first onthose portions of the front from500 feet to 2,000 feet (152 to 610m) above the valley bottom,because this is the zone of the ther-mal belt. Within this zone you canexpect the least benefit fromincreased fuel moisture at night.

WindAlthough fuel moisture is the criti-cal variable that puts all fuel typesin an explosive condition, orreduces them to an easy job of firecontrol, wind velocity is often thestraw that breaks the camels back.In fact, at fuel moistures of 6 or 7percent up to 20 or 25 percent,wind is often the variable which

Calculating the probabilities means carefulconsideration of every available source of

information concerning each of the basic factorsof fire behavior.


finally determines what a fire willdo. Some basic research by Fons atthe California station has shownthat with fuel moisture at 8 per-cent, variations of wind velocity aremore significant in changing therate of spread than are variations infuel temperature, fuel size, com-pactness, or density.

Whether or not some fire seasonsare, as a whole, windier than othersI do not know. But we do know thatwind is a result of certain meteoro-logical conditions which changeperiodically at from 3- to 5- or 6-day intervals. If you will watch thewind record portion of any fire dan-ger station chart, particularly for alookout station, you will see a grad-ual increase of wind for severaldays, then a decrease, then anotherincrease. Obviously, by watchingthis up and down trend you candefinitely improve your calculationof the probabilities, even thoughyou cannot forecast precisely.

There are a few general rules ofwind behavior which can be usedlocally in Region 1. First is a dis-covery, made by Hayes anddescribed in Circular 591, that theplaces of greatest wind danger atnight are, strange as it may seem,the north aspects at high altitudes.To put it another way: While youcan usually count on the winddying down during the night in thevalley bottom, you should notcount on this if your fire is up onthe high divides between majordrainages. Instead, at the higherelevations you should expect thehighest winds at night, not in thedaytime, and more wind on thenorth aspects than on the south.

Another general law of wind behav-ior during the ordinary fair weatherof June, July, and August, that isquite well known, is that during theday the wind usually blows up thecanyon or creek, while during thenight it blows down canyon. Thisreversal of direction in the eveningusually takes place just a few min-utes after sundown. When both thedaytime and the night winds arevery lightless than 4 miles perhour (6 km/h)this reversal maynot be of much significance.However, in topography and onareas which are materially heatedby the suns rays, the afternoonwind created by rising hot air mayamount to 8 or 10 miles per hour(1316 km/h). When this is thecase, reversals at sundown may pro-duce a significant down-canyonwind. This condition is most pro-nounced on south aspects and inwatersheds draining toward thesouth into a big canyon runningeast and west, like that of theSalmon River. But even under theseconditions, a large fire may createsuch an updraft as to upset the nor-mal reversal of wind. Hence, whilethis generality is worth consideringin your calculations there are otherfactors which also must be recog-nized before you make your finalestimate of rate of spread.

From what has been said it shouldbe clearly evident that calculatingthe probabilities means doingmuch, very much more than justfight a fire with brute

Fire Management Today Volume 64 • No. 1 • Winter 2004

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Transcript of Fire Management Today Volume 64 • No. 1 • Winter 2004