BiomechanicalAnalysis of GrubbingTechnique in the Use ofFire Handtools—A Synopsis

United States

Department of

Agriculture

Forest Service

Technology &

Development

Program

5100—Fire Management

May 2003

0351 1204—SDTDC

FOREST SERVICE

DEP A R T MENT OF AGRICUL T U R

E

Lois P. SickingBiomechanics Engineer

San Dimas Technology and Development CenterSan Dimas California 91773–3198

BiomechanicalAnalysis of GrubbingTechnique in the Use of FireHandtools—A Synopsis

Information contained in this document has been developed for the guid-ance of employees of the U.S. Department of Agriculture (USDA) ForestService, its contractors, and cooperating Federal and State agencies. TheUSDA Forest Service assumes no responsibility for the interpretation oruse of this information by other than its own employees. The use of trade,firm, or corporation names is for the information and convenience of thereader. Such use does not constitute an official evaluation, conclusion, rec-ommendation, endorsement, or approval of any product or service to theexclusion of others that may be suitable.

The U.S. Department of Agriculture (USDA) prohibits discrimination in allits programs and activities on the basis of race, color, national origin, sex,religion, age, disability, political beliefs, sexual orientation, or marital or familystatus. (Not all prohibited bases apply to all programs.) Persons with dis-abilities who require alternative means for communication of program in-formation (Braille, large print, audiotape, etc.) should contact USDA’s TAR-GET Center at (202) 720-2600 (voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office of CivilRights, Room 326-W, Whitten Building, 1400 Independence Avenue, SW,Washington, D.C. 20250-9410 or call (202) 720-5964 (voice and TDD).USDA is an equal opportunity provider and employer.

TABLE OF CONTENTS

INTRODUCTION .......................................................................................................... 1

BACKGROUND ............................................................................................................. 1

ERGONOMIC PRINCIPLES FOR USE IN WILDLAND FIREFIGHTING ........................... 1

Grip Strength, Glove, and Handle Surface ............................................................... 2

Fitness for Firefighters .............................................................................................. 2

CONCLUSIONS............................................................................................................. 3

Key Biomechanical Parameters ................................................................................ 4

Survey Results ......................................................................................................... 7

Proposed Training Program ...................................................................................... 7

RECOMMENDATIONS .................................................................................................. 9

1

INTRODUCTIONErgonomics is the study of how humans andmachines work together best, therebyreducing the potential for injury, improvingsafety, and increasing productivity. In wildlandfirefighting, using ergonomic principles canprevent or minimize injuries to firefighters,enhance safety, and increase the amount offireline. Using such principles can reducefirefighter compensation claims, increaseemployee retention, provide for a higherpercentage of skilled firefighters, improveemployee morale, and establish a safer, moreproductive workforce.

The body posture, motions, and tool swingtechniques of 22 firefighters from 5 forestsusing the standard pulaski, super pulaski, andthe combination (combi) tools were evaluatedusing a magnetic motion capture/analysissystem. The tool testing was videotaped andevaluated for each firefighter’s skill level.Based on this evaluation by the InteragencyHotshot Crew Superintendent and AssistantSuperintendent, workers/firefighters werecategorically grouped—by skill level—aseither a regular or skilled firefighter.

As expected, the motions of a skilledfirefighter varied significantly from those of aregular firefighter. Bend-over angle, shoulderposition, grip, separation of hands, positionrelative to fireline, tool displacement, toolstroke rate, and tool head path varied widely.

The San Dimas Technology and DevelopmentCenter (SDTDC) biomechanics engineernoticed that regular firefighters used arm andshoulder muscles primarily to power fire tools.In direct contrast, skilled firefighters used legand trunk muscles mainly, and arm andshoulder muscles sparingly. Arm and shouldermuscles are significantly smaller than leg andtrunk muscles. Regular firefighters were

expected to fatigue much more quickly due tothe size difference of these muscles.Consequently, it is important to describe indetail the body posture, motions, and toolswing techniques of skilled firefighters usingprimarily leg and trunk muscles for grubbing.This study provided an opportunity to captureand use the knowledge of veteran firefightersto train new and less experienced firefighters.

BACKGROUNDSDTDC has conducted several fire handtoolstudies, including a fire tool survey offirefighters regarding specialty fire tools,modified fire tools, and fiberglass handles.The survey also included questions about howbalanced fire tools are and how various widthsof the pulaski hoe blade affected constructionof a fireline.

Data analysis from a previous fire tool studyconducted by the SDTDC biomechanicsengineer indicated that the greatestimprovement in safety and fireline production,especially for Type II crews, could come fromtraining these crews to achieve the bestgrubbing technique with the standard andsuper pulaskis and the combination (combi)tool. The biomechanics engineer maderecommendations for determining the optimumgrubbing technique and for developing atraining program both to teach regularfirefighters how best to use fire handtools andto provide a review for skilled firefighters. Theengineer developed a preliminary trainingprogram that is described in the Tech Tips,0251-1302-SDTDC.

ERGONOMIC PRINCIPLES FOR USE INWILDLAND FIREFIGHTINGLow back pain and carpal tunnel syndromewere the two most common firefighter healthconcerns commented on in the earlier SDTDCfire tool survey. These conditions are best

2

evaluated by a detailed motion analysis.Factors related to these two health conditionsare the level of physical fitness, abdominalmuscle strength, and trunk muscle balanceand the incidence of repetitive heavy lifting,bending, twisting, awkward postures, fatigue,emotional stress, and even cigarette smoking.Other important ergonomic considerations aretype and design of gloves, amount of handgripstrength, and how to achieve and maintain thelevel of physical fitness necessary for wildlandfirefighters.

Grip Strength, Gloves, and Handle SurfaceFirefighters make an effort to increase gripstrength by turning gloves inside out, exposingthe glove seams to increase the glove surfacearea making contact with the tool handle. Inaddition, some Interagency Hotshot Crew(IHC) firefighters buy “structure” type gloveswith personal funds. These gloves have arough outside surface, thinner seams, and noseams in the palm; all aspects that increasegrip strength. Structure gloves typically extendat least 4 inches past the wrist, important inpreventing embers, dirt, and debris fromgetting into the gloves. Gloves with seamsbetween the fingers and on the palm interfere

with grip development. Thick gloves withseams can reduce grip strength up to 40percent.

Decreased grip strength results in incidents ofdropped tools, poor tool control, low workquality, and increased fatigue. Some IHCsroughen the tool handle surface by removinghandle varnish, increasing the friction value toenhance gripping action.

Fitness for FirefightersFitness is the most important factor inpredicting the ability to build fireline at asustainable work rate without experiencingundue fatigue or creating a safety hazard foryourself or other firefighters. Many Federaland State agencies have used the step test topredict aerobic fitness. Fitness cannot berushed. Achieving fitness is a gradual processthat may require an exercise program of 6weeks or more. Firefighters are wise to trainfor physical fitness before the fire seasonbegins, not while on the fireline. See theNational Wildfire Coordinating Grouppublication, “Fitness and Work Capacity,” forguidance on achieving and maintainingphysical fitness for firefighters.

3

CONCLUSIONSBased on the biomechanics testing, the combi tool was superior to the standard and super pulaskiin regard to safety aspects, low energy cost, and high productivity, especially for the regularfirefighter. The combi tool should be the first tool used to train regular firefighters in developingskilled grubbing technique and in becoming more efficient. The combi tool should also bedesignated as the best grubbing tool in light flashy fuels and whenever fuel type and soil conditionspermit.

Participants ranked the combi tool effectiveness and quality of line as the lowest for all tools,indicating a strong tool bias and low field acceptability. The benefits of the combi tool have notbeen fully realized. The fire community should give top priority to a broad field implementation ofthe combi tool and include it in crew tool mixes, especially for Type II crews. See table 1.

Table 1. Participant ranking of the standard pulaski, super pulaski, and combi tools

Regular SkilledStandard Super Standard Superpulaski pulaski Combi pulaski pulaski Combi

Quality of line 0 2 -5 3 5 4

Effectiveness 1 1 -1 3 5 1

Versatility 0 0 2 4 2 3

Less fatigue—hand and arm -1 -3 3 -3 -4 1

Less fatigue—lower back 2 1 3 -3 -4 1

Safety—control 1 -1 4 4 2 1

Less shock—handle absorption 2 1 2 2 1 4

Better grip 2 0 4 2 1 4

Key for ranking:

Most negative = -5 No difference = 0 Most positive = +5

The biomechanics test results show that regular firefighters used different muscle sets whilegrubbing with the test tools compared to skilled firefighters. Skilled firefighters primarily used legand trunk muscles with the standard and super pulaski, while regular firefighters primarily used thesmaller arm and shoulder muscles. Due to the size difference of these muscle sets, regularfirefighters using the standard and super pulaski are expected to fatigue faster than skilledfirefighters.

Regular firefighters using the combi tool employed less of the smaller arm and shoulder musclesand more of the larger leg and trunk muscles. Consequently, regular firefighters are not expectedto fatigue as quickly using the combi tool because large leg and trunk muscles are used. Regularfirefighters are expected to fatigue more quickly using the standard and super pulaski becausethey primarily use their smaller arm and shoulder muscles compared to use of the combi tool,where more large leg and trunk muscles were used.

4

Use of the super pulaski also increases thepotential for injury for firefighters with a poorgrip and decreased upper body strength. Thecombi tool is the safer, more efficient tool forregular firefighters to develop their skills.

Key Biomechanical ParametersOverall, skilled firefighters generated smooth,consistent motions, regardless of body size orgender. Conversely, the regular firefightershad more variation in body posture and toolswing motions. Key differences betweenskilled and regular firefighters in body posture,grubbing motions, productivity, energyexpended, and potential for injury are bestdescribed by the following:

Energy expenditure—Compared to thestandard and super pulaski, the combi toolhas the lowest energy expenditure for thesame amount of work. Consequently, thecombi tool is the most efficient tool tested.

Regular firefighters using a standard pulaskior a combi tool expend the same amount ofenergy in two cycles that a skilled firefighterexpends in three cycles simply by lifting thetool head higher. Regular firefighters using thesuper pulaski expend the same amount ofenergy in one cycle as a skilled firefighterexpends in two cycles simply by lifting the toolhead higher. This difference in motion cyclesand tool lift height between regular and skilledfirefighters indicates a need for training.

Even though the cycles are the same betweenthe standard pulaski and the combi tool,several differences in tool design significantlyaffect energy expenditure. The combi toolweighs 18 percent less than the standardpulaski and is a more balanced tool. It has alightweight tool head and most of its weight inthe handle, unlike the pulaski. The combi toollift height is 12 inches for the skilled firefighterversus 20 inches for the standard pulaski.

This small lift height is further offset by a 40-inch-long combi tool handle versus a handle of34 inches for the pulaski. Consequently, thecombi tool has the lowest energy expenditurefor the same amount of work as compared tothe standard and super pulaski.

Body posture—When regular and skilledfirefighters used the combi tool, their bodyposture at maximum lift height and tool strikedid not vary as significantly as when they usedthe standard and super pulaski. This indicatesthat the combi tool should be the easiest toolfor training regular firefighters to becomeskilled firefighters.

Crew production rates—Based on standardhand crew production rates for medium brushfor a line width of 6 feet, skilled firefighterscan complete 75 tool strikes for every 55 by aregular firefighter using the standard pulaski.If the whole crew was trained to the skilledlevel, productivity could increase by 68 feetper hour. That is comparable to having 2people added to a 15-person crew.

With the super pulaski, skilled firefighterscomplete 75 tool strikes for every 40 by aregular firefighter. If the whole crew wastrained to the skilled level, productivity couldincrease by 136 feet per hour. That iscomparable to having 4 people added to a 15-person crew.

With the combi tool, skilled firefighters cancomplete 86 tool strikes for every 67 by aregular firefighter. If the whole crew wastrained to the skilled level, productivity couldincrease by 55 feet per hour. That iscomparable to having 2 people added to a 15-person crew.

Tool-Head Impact—Tool-head impact forcewas substantially higher for regular firefightersthan for skilled firefighters. The regular

5

firefighters increased lift height and extendedreach contributed to the tool-head impactforce and could cause back injury. Increasedlift height requires back exertion. Because ofthe angular velocity caused by the extendedreach, the tool is buried further in the ground.Freeing a tool blade that is buried further inthe ground and completing the motion cyclecauses strain on the back.

The tool impact force for a regular firefighterusing the standard pulaski was 4.5 g,compared to the skilled firefighter with animpact force of 2.7 g. This means the regularfirefighter pounded the ground 67 percentharder than a skilled firefighter with thestandard pulaski. The tool impact force for aregular firefighter using the super pulaski was5.3 g, compared to the skilled firefighter withan impact force of 2.9 g. Therefore, theregular firefighter pounded the ground 83percent harder than a skilled firefighter withthe super pulaski. The tool impact force for aregular firefighter using the combi tool was 3.0g, compared to the skilled firefighter toolimpact force of 1.8 g. This means the regularfirefighter pounded the ground 67 percentharder than the skilled firefighter with thestandard pulaski. See figure 1.

Figure 1—Tool impact force or acceleration comparisonof skilled versus regular firefighters with the standardpulaski.

Tool-Head Height—As described in theprevious section, an increased tool lift heightis due in part to an increased arm reach,causing increased work on the back andinefficient use of energy. Tool lift height can bereduced to an optimum lift with propertraining. A regular firefighter elevates thestandard pulaski tool head to 32 inches, 60percent higher than a skilled firefighter at 20inches. See figure 2. A regular firefighterelevates the super pulaski tool head to 41inches, 78 percent higher than a skilledfirefighter at 23 inches. A regular firefighterelevates the combi tool head to 21 inches, 75percent higher than a skilled firefighter at 12inches.

Figure 2—Tool lift height comparison of skilled versusregular firefighters with the standard pulaski.

Tool Strike Rate—The standard pulaski has a3-inch hoe blade. The regular firefighter canstrike or grub 55 strikes per minute, or 165inches per minute. With 75 strikes per minute,the skilled firefighter can strike or grub 225inches per minute using the standard pulaski.Skilled firefighters are 36 percent moreproductive as determined by tool strike ratewith the standard pulaski. See figure 3.

6

Figure 3—Tool motion cycle or stoke/strike ratecomparison of skilled versus regular firefighters with thestandard pulaski.

The super pulaski used in this study had a6.8-inch hoe blade. The regular firefighter cangrub 40 strikes per minute or 272 inches perminute. The skilled firefighter can grub 75strikes per minute or 510 inches per minutewith the super pulaski. Skilled firefighters are88 percent more productive as determined bytool strike rate with the super pulaski.However, a previous SDTDC fire tool studydemonstrated that the substantial increase inenergy cost to the firefighter far exceeds theproduction increase. In addition, use of someconfigurations of the super pulaski haveraised safety concerns.

The combi tool has a 4-inch serrated blade.With 67 strikes per minute, the regularfirefighter can strike 268 inches per minute.With 86 strikes per minute, the skilledfirefighter can strike 344 inches per minutewith the combi tool. Skilled firefighters are 28percent more productive as determined by toolstrike with the combi tool. The combi tool isthe most efficient tool based on the lowenergy cost, high productivity, and safety,especially for the regular firefighter.

Physical Fitness—Significant differences inlevels of physical fitness exist between regularand skilled firefighters. The time required forthe 12-mile run was 40 percent higher andpercent body fat was 50 percent higher inregular firefighters compared to skilledfirefighters. This indicates a substantiallylower level of physical fitness, which is criticalto firefighter performance and increases thepotential for accidents or injury. Anappropriate minimum performance standardbased on physical requirements for skilledfirefighters is crucial to safety. In addition, it isimportant to have a reserve physical fitnesscapacity available for use in emergencies.These findings indicate that minimumperformance standards need to be revised toa higher level of physical fitness. Specificsteps for wildland firefighters to achieve andmaintain fitness and work capacity are clearlydescribed in the National Wildfire CoordinatingGroup publication, “Fitness and WorkCapacity.”

Firefighters can reduce the potential for carpaltunnel syndrome and other injuries by beingphysically fit for the job, using the bestgrubbing technique for each fire tool, takingfrequent rest breaks, rotating tools acrossfirefighters, and holding tools with a morenatural hand position for good gripping action.These are especially important for Type IIcrews who are typically less work-hardenedthan Type I IHC crews.

New tool configurations should be developedwith optimal user technique design criteria toinclude a balanced, lightweight tool head,ergonomic handle, and optimum hoe bladewidth and handle length, with safety andproduction as the ultimate criteria.

7

Safety—Analysis of key biomechanicalparameters with the use of the super pulaskiidentified a significant safety concern. Regularfirefighters lack good control and guidance ofthe super pulaski. It is lifted higher and has agreater tool head mass, contributing toincreased momentum on the downstroke withthe nondominant foot in the tool head path.Lost time studies related to fire handtools,specifically the super pulaski, have not beenconducted. Regular firefighters should bediscouraged from using the super pulaskimodel with a 6.8-inch blade width until theproper training and minimum physicalstandards, including grip and upper bodystrength, have been defined and implementedto address the increased angular accelerationand twist on impact. Exercises with ahandspring device can increase grip strength.

Survey ResultsThe fire tool survey of the IHC network had aresponse rate of 75 percent, with submissionof tool modification information, includinghardware and drawings of standard, modified,and specialty fire handtools in service. Theresponse indicates a high level of interest intool design and use. Modifications varied fromcrude to prototype models that met someaspects of basic handtool design criteria.Some of the modified tools have wide fieldacceptance, such as the Bosley andRhinehart. Some modifications of the standardpulaski are refined designs with a hoe bladewidth of 4.5 inches. Some of these toolmodifications warrant further study. The reportof findings to the field should include pros andcons of commercial and field tool

modifications with associated science-baseddesign rationale.

Proposed Training ProgramBy using the proposed training programdescribed in Tech Tips 0251-1302-SDTDC,Type I and II crews can readily acquire thenecessary skills to use fire handtools moreeffectively and safely, including the primaryuse of leg and trunk muscles to provide asustainable work rate. This training programwas developed to implement the five principlefactors of skilled grubbing and the primary useof leg and trunk muscles, including tool liftheight, work cycle time (stroke rate), handseparation, right shoulder angle, and positionof the feet. See figures 4a and 4b.

The proposed training program needs furtherrefinement with the assistance of crewbosses, to include printed and electroniccomputer training modules, posters, andvideos. Training material based on keybiomechanical parameters and pacing for asustainable work rate needs to be developed.Skilled firefighters pace themselves tomaintain a sustainable work rate. They appearto use the same amount of power by varyinglift height according to tool weight, exercisingless lift for more given weight, andcompensating for tool head weight bypositioning the hands more closely to the toolhead as weight increases. The SDTDCbiomechanics staff should conduct resultsverification testing with field evaluation inseveral regions to determine whether thetraining module is effective.

8

SKILLED WORKERS• Have the dominant foot slightly forward and

essentially parallel to the tool path; thenondominant foot is 60 degrees off thedominant foot.

• Flex knees and keep the back straight, bentat the waist at an angle almost parallel tothe ground.

• Keep the tool blade angled away from thebody, with feet positioned out of the way ofthe swing of the tool blade.

• Keep the back position almost steady duringthe tool swing.

• Use leg and trunk muscles for grubbing.

REGULAR WORKERS• Position the nondominant foot slightly

forward and intersecting the tool path.

• Flex the knees and may or may not keepthe back straight.

• Stand more upright, bent at the waist butthe back is not parallel to the ground.

• Move the back in a bobbing motion anduse arm and shoulder muscles for grubbing.

• Angle the tool blade towards thenondominant foot in the tool swing path.Stop the tool swing short of the foot.

• May use an increased arm reach tocompensate for the difference in bodyposture relative to the fireline.

FEET

TOOL PATH

TO

OL

SW

ING

DIR

ECT

ION

Position of pelvis

FEET

TOOL PATH

TO

OL S

WIN

GD

IRE

CT

ION

Position of pelvis

Figure 4a—Regular firefighter body posture and toolswing path.

Figure 4b—Skilled firefighter body posture and toolswing path.

9

For verification testing, the SDTDCbiomechanics staff should conduct abiomechanical evaluation of regularfirefighters trained to the newly definedparameters and retest the firefighters at thenew skill level. A comparative analysis wouldbe conducted between the before-and-aftertraining data.

To improve performance with an expectedcorresponding reduction in ergonomicallyinduced injuries, the SDTDC biomechanicsstaff should identify optimum biomechanicsassociated with the use of the shovel andMcLeod handtools. This biomechanical datacan be used to conduct a quantitativedynamics and acceleration data comparativeanalysis between skilled and regularfirefighters to determine the amount of stresson joints. Measuring and understanding thenet dynamic moments and forces offirefighters from kinematic data, body segmentmass and dimension parameters, force plateground reaction vectors, and kinematic andkinetic data can also help in developingtechniques to reduce stress on joints.

RECOMMENDATIONSThe following recommendations weredeveloped based on the conclusions:

• Give top priority to the broad fieldimplementation of the combi tool,increasing field acceptance, and includingthe combi tool in crew mixes, especiallyfor Type II crews. Use the combi tool asthe first training tool for regularfirefighters in developing a skilledtechnique and in training experiencedfirefighters to become more efficient. Inaddition, designate the combi tool as thepreferred grubbing tool in light flashyfuels in decomposed granite and when

fuel type and soil conditions permit asdetermined by the low-energy cost, highproductivity, and safety aspects of thecombi tool when compared to thestandard and super pulaskis.

• Discourage regular firefighters from usingthe super pulaski model with a 6-inch orgreater hoe blade width until appropriateminimum physical standards, includinggrip and upper body strength, have beendefined and implemented. Conduct a losttime study related to fire handtools,specifically the super pulaski, to identifysafety issues.

• Develop a training program to teachfirefighters, especially Type II crews, thenecessary skills to use fire handtoolsmore effectively and safely, incorporatingthe primary use of leg and trunk muscles,key biomechanics parameters, andpacing for a sustainable work rate. Thistraining program could also teach Type Icrews to improve efficiency. Refine theproposed training program with theassistance of crew bosses, including hardcopy and electronic computer trainingmodules, posters, and videos.

• Revise minimum performance standardsfor firefighters to establish a higher levelof physical fitness and work capacity.Encourage wildland firefighters to achieveand maintain fitness and work capacity asdescribed in the National WildfireCoordinating Group publication, “Fitnessand Work Capacity.”

• Identify the optimum biomechanicsassociated with the use of the shovel andMcLeod handtools in order to improveperformance, with an expectedcorresponding reduction in ergonomicallyinduced injuries.

10

• Develop new tool configurations based onrigorous scientific methodology, firefighterinput, cutting ability, tool balance,kinematics, and safety. Field-test thehandtools in a variety of fuels and soilcompactions. Redesign tools to follow thefire tool experimental design matrix.

• Establish a balanced configuration of allstandard fire tools, including bringing thecenter of gravity in line with the handlecenterline. Balancing of tools may includeincreasing the handle length of thepulaski and reducing the diameter andhandle length of the combi tool, asappropriate. Determine the optimum widthof the pulaski hoe blade.

• Further analyze data from the SDTDC firetool survey and publish the findings in areport or catalog for field distribution.Include various commercially availablespecialty fire handtools and the pros andcons of commercial and field toolmodifications listed with associatedscience-based design rationale in thereport.

For further information, contact the fireprogram leader by phone at 909–599–1267 orby e-mail at mailroom_wo_sdtdc@fs.fed.us.