BiomechanicalAnalysis of Grubbing

Technique in the Use ofFire Hand Tools

United StatesDepartment ofAgriculture

Forest Service

Technology &DevelopmentProgram

5100—Fire ManagementMay 20000051 1201—SDTDC

FOREST SERVICE

DEP A R T MENT OF AGRICUL T U R

E

Lois P. SickingMechanical Engineer*

San Dimas Technology and Development CenterSan Dimas California 91773-3198

* In addition, the author is licensed topractice as a Registered Nurse in the states of

California and Texas, with Advanced Cardiac Life Support (ACLS) certification by the

American Red Cross.

BiomechanicalAnalysis of Grubbing

Technique in the Use of FireHand Tools

Information contained in this document has been developed for the guidance ofemployees of the Forest Service, USDA, its contractors, and cooperating Federaland State agencies. The Department of Agriculture assumes no responsibility forthe interpretation or use of this information by other than its own employees. Theuse of trade, firm, or corporation names is for the information and convenience ofthe reader. Such use does not constitute an official evaluation, conclusion,recommendation, endorsement, or approval of any product or service to theexclusion of others that may be suitable.

The US Department of Agriculture (USDA) prohibits discrimination in its programsand activities on the basis of race, color, national origin, sex, religion, age, disability,political beliefs, and marital or familial status. (Not all prohibited bases apply to allprograms.) Persons with disabilities who require alternative means forcommunication of program information (Braille, large print, audiotape, etc.) shouldcontact USDA Office of Communications at 1-202-720-2791 (voice), or1-800-855-1234 (TDD).

To file a complaint, write the Secretary of Agriculture, US Department of Agriculture,Washington, DC 20250, or call 1-800-245-6340 (voice), or 1-800-855-1234 (TDD).USDA is an equal employment opportunity employer.

Acknowledgements

This report is the result of the efforts of many Forest Service employees,retired Forest Service specialists, contractors, and cooperating Federaland State agencies. In addition, the following people have contributed:

Bob SerratoRegion 5

Dalton Interagency Hotshot Crew Superintendent

Tony SciaccaRegion 3

Prescott Interagency Hotshot Crew Superintendent

David ConklinRegion 5

Bear Divide Interagency Hotshot Crew Superintendent

Phillip CheethamPh.D. Candidate Biomechanics

Arizona State University

Eric MallettPh.D. Candidate Biomechanics

Arizona State University

Brian J. SharkeyPh.D. Exercise Physiology

University of Montana

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A special measure of gratitudeand mention goes to the familyof Art Jukkala for his efforts withthis project, especially in fieldtesting, and the review of the testplans and reports.

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TABLE OF CONTENTS

INTRODUCTION AND SCOPE...................................................................................... 1

PREVIOUS FIRE TOOL STUDIES .................................................................................... 1

ERGONOMIC CONSIDERATIONS ................................................................................ 3Carpal Tunnel Syndrome ......................................................................................... 4Low Back Pain ......................................................................................................... 5

ERGONOMIC FACTORSGrip Strength. .......................................................................................................... 6Physical Fitness ....................................................................................................... 7

BIOMECHANICAL TEST PARAMETERS .......................................................................... 8

TEST PROCEDURE AND INSTRUMENTATION.............................................................. 8Test Tools ................................................................................................................. 9Preparation for Testing ........................................................................................... 10Detailed Test Method ............................................................................................. 11Determination of Skilled and Regular Firefighters .................................................. 12

DETAILED DATA ANALYSIS BY TOOL .......................................................................... 12Standard Pulaski .................................................................................................... 13Super Pulaski ......................................................................................................... 20Combi Tool ............................................................................................................ 28

DETAILED DATA ANALYSIS BY BIOMECHANICAL PARAMETERTool Acceleration/Force At Impact ......................................................................... 35Tool Lift Height ...................................................................................................... 35Work Cycle Time ................................................................................................... 36Hand Separation ................................................................................................... 36Wrist Rotation Joint Angle Profile .......................................................................... 36Shoulder Extension Angle and Arm Reach ............................................................. 39Critical Biomechanical Parameters ........................................................................ 42Proposed Training Program .................................................................................... 42Participant Ranking of Tools ................................................................................... 45Experience, Strength, and Fitness Scores ................................................................ 46Participant Comments............................................................................................ 47

DISCUSSION ............................................................................................................... 47

CONCLUSIONS........................................................................................................... 48

RECOMMENDATIONS ................................................................................................ 53

BIBLIOGRAPHY........................................................................................................... 55

APPENDIXESA. Definitions ........................................................................................................ 59

B. Fire Hand Tool Test Matrix ................................................................................. 61

C. Biomechanics of Fire Hand Tools Test Matrix ..................................................... 63

D. Preference Rating of Hand Tools ....................................................................... 65

E. Biomechanical Angle Profiles and Angular Velocity Profiles ............................... 67

F. Biomechanical Tables of Values .......................................................................... 69

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INTRODUCTION AND SCOPEErgonomics is the study of optimizing the humantool system, thereby reducing the potential forinjury, improving safety, and increasingproductivity. Ergonomic principles can be usedto prevent or minimize injuries in firefighters usingfire hand tools in wildland firefighting. Theemphasis is on changing the tool, user technique,and environment rather than changing peopleto fit the tool. In this way priority is given to thecapabilities, needs, and limitations of people. Aminimum performance standard based on jobphysical requirements is fundamental.Ergonomics, sometimes called human factors,discovers and applies information about humanbehavior, abilities, limitations, and othercharacteristics to the design of tools, machines,systems, tasks, jobs, and environments forproductive, safe, comfortable, and effectivehuman use (1).

There has been a progressive effort to evaluateand redesign hand tools used in wildland fireservice for fireline construction. In recent years,fire tool testing by the San Dimas Technologyand Development Center (SDTDC) has focusedon tool design and most recently on firefighterbiomechanics.

Biomechanical measurements provide insight intothe abilities and limitations of the human bodywhile generating grubbing motions with fire handtools. Identification of the optimum biomechanicsassociated with the use of hand tools cancontribute to improvements in performance witha reduction in ergonomically induced injuries.SDTDC was tasked to:

• Conduct a biomechanical evaluation offirefighters using fire hand tools

• Determine the critical biomechanicalparameters associated with grubbing

• Describe the biomechanics of regular andskilled grubbing technique

• Conduct a comparative analysis of regularand skilled grubbing technique

• Report findings.

This information can be used to train firefightersfor ergonomic efficiency, improved performance,and increased worker safety. In addition, handtool design modifications were derived from thesekinematic measurements.

The standard Pulaski, Super Pulaski, andCombination (Combi) hand tools were tested witha sample size of 22 firefighters. Applicablebiomechanical parameters were determined tobe left and right shoulder joint angle profiles,wrist range of motion, joint angular velocityprofiles, peak angular velocities, body postureat maximum tool lift height and tool impact, motioncycle time, tool lift height, tool head path, andtool acceleration/force on impact. Definitions ofterms relative to the context of this report areprovided in Appendix A.

PREVIOUS FIRE TOOL STUDIESFire tool testing by the Missoula Technology andDevelopment Center (MTDC), as described inAn Improved Wildland Fire Fighting Tool, includeda field evaluation, with efficiency defined as theamount of fireline in feet versus the amount ofenergy expended to produce fireline. Productivitywas in terms of feet per minute. The Combi toolwas described in this study as a multipurposefire hand tool with a higher level of productivityas compared to the standard and Super Pulaski.It was reported that the Super Pulaski had a highenergy cost in relation to the increase inproduction. There also was a safety concern.Firefighters with a poor grip and decreased upperbody strength had a greater potential for injurywith the use of the Super Pulaski (2).

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National interest propelled an initial study bySDTDC regarding tool redesign (3). Thiscombined qualitative and quantitative studycompared the hoe blade of commonly usedgrubbing tools to include the mini, standard andSuper Pulaskis, and the standard Pulaski witha fiberglass handle. The goal was to determinetool configurations that best balancedphysiological characteristics with optimumproduction of fire line and firefighter safety.Although several areas of refinement wereneeded, the study concluded that regardless ofindividual size, physical condition, or rate at whicha firefighter grubs, the Super Pulaski couldproduce more line than the standard or miniPulaski tools. However, the energy costs weremuch higher than the increased output. Inaddition, a safety concern was identifiedassociated with the increase in the tool head massof the Super Pulaski. An increase in tool headmass increases angular acceleration during thedown swing phase of motion, resulting in anincrease in tool rotation on impact, with anincrease in stress on the wrists. In other words,the heavier the tool head, the greater thetendency to twist especially when the tool headhits the ground. This is felt as a stinging sensationof the hands and increased fatigue in the wrists.

A fire tool survey of the Interagency Hotshot Crew(IHC) network was conducted by SDTDC priorto the initial study in order to collect information,hardware, and drawings on standard, modified,and specialty fire hand tools in service. Thissurvey revealed that the Pulaski was the mostcommon fire tool in use and the most commonfire tool modified.

Modifications typically increased blade width, asin the Super Pulaski, which increased tool headmass, and raised a safety concern. Consequently,the standard and Super Pulaski were selectedfor further study. The Combi tool was includedas the reference grubbing tool for comparisonbased on high productivity rates.

The benefit derived from this initial study wasthat applied scientific methodology provided apositive contribution to the tool selectionprocess (4). Efforts from this study resulted inthe development of a procedure for hand toolevaluation; an efficiency rating of hand toolsbased on field test performance, measuringgrubbing tool production in terms of weight ofmaterial moved per unit of time, againstergonomic input in terms of calories per unit oftime expended; and a preference rating of handtools based on subjective responses/opinionsof the test workers (3).

Kinematic testing was proposed in order toevaluate the potential for tool design, expandingthe research and tool evaluation effortsrecommended in the initial study. An investigationrevealed that new technology in measuringhuman-tool kinematics had been developed andwas commercially available. Field testing wasconducted with the magnetic motion capture/analysis system as indicated in figure 1. It wasdetermined that this system had practicalapplications in fire tool studies. It was furthernoted from a preliminary biomechanical analysisthat the motions of a skilled firefighter variedsignificantly from those of a regular firefighter.There was a wide variance in tool swingtechnique/motions and body posture, in termsof bend-over angle, shoulder position, grip,separation of hands, position relative to fireline,tool displacement, tool stroke rate, and tool headpath (5).

Regular workers were observed to assume a bodyposture primarily using arm and shoulder musclesto power fire tools. In direct contrast, skilledworkers were observed using the larger leg andtrunk muscles mainly, and the significantly smallerarm and shoulder muscles sparingly. Arm andshoulder muscles are significantly smaller thanleg and trunk muscles. Consequently, regularworkers were expected to fatigue much morequickly due to the size difference of these

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muscles. It was determined that a biomechanical analysiscould detail the body posture and tool swing techniquesof skilled firefighters primarily using their leg and trunkmuscles for grubbing.

Figure 1—Field testing with position/angle motioncapture/analysis system.

From these findings, it was recommended that further effortsbe directed to investigating optimum user technique in termsof body posture and tool swing techniques of skilledfirefighters who use primarily leg and trunk muscles forgrubbing. Furthermore, a formal training course for the useof fire hand tools is not available and firefighters receiveinformal training with varying degrees of proficiency at thelocal level.

ERGONOMIC CONSIDERATIONSErgonomic principles can be used to prevent or minimizeinjuries in the workplace, specifically in the use of handtools. Ergonomic concerns, once identified, can beaddressed and optimized. Information gathering regardingergonomic concerns can be obtained by several differentmethods. These methods include employee lost time injuryreports, worker surveys, and general observations as theemployee works. Worker compensation costs forergonomically induced injuries are substantial.

Employee incident and injury recordsprovide important statistically basedinformation regarding ergonomicissues in terms of lost time and injurycosts/trends (6). Firefighter lost time/injury analysis and trends have notbeen conducted for the use of fire handtools. However, a survey regarding thedesign and use of standard fire handtools by IHC’s and general observationhas been conducted (3,7).

Firefighter comments from this fire toolsurvey identified low back pain andsymptoms of carpal tunnel syndromeas the two most common health areasof concern. This survey alsodetermined that IHC’s modify many ofthe tools they use. Furthermore, minormodifications to gloves were beingperformed. Some IHC firefighters havereported turning gloves inside out inan attempt to increase grip strength.This action involves exposing the gloveseams, thereby increasing glovesurface area making contact with thetool handle. Incidents of turning glovesinside out have decreased since thesewildland firefighter gloves wereredesigned in 1995, with better seamdesign, improved sizing and shorterwelts, or seam edges (8).

Some IHC firefighters have describeda desire for a glove with even smallerseams, no seams on the palm, andgloves that extend several inchesabove the wrist, as compared to theredesigned wildland gloves. Therehave been reports of some IHCfirefighters buying “structure” typegloves using personal funds. Thesegloves have a rough outside surface,thinner seams, and no seams in thepalm, all aspects that increase grip

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strength. Also, they typically extend at least4 inches past the wrist, important in preventingembers, dirt, and debris from getting into thegloves. In addition, some IHC firefighters roughenup the tool handle surface by removing handlevarnish to increase the friction value, increasinggripping action. Gripping strength can beincreased by exercising with a handspring device.Current research indicates that ergonomic areas ofconcern should be investigated when workers havedesigned or modified their own tools or PPE (9).

General observations of firefighters grubbing withstandard fire tools and several new hand toolconstructions provided direction into a keyergonomic consideration, biomechanics. A widevariance in tool swing technique/motions andbody posture associated with the use of fire handtools was apparent during field testing.

From these findings, project efforts were directedto investigating user technique, in terms of thebiomechanics of grubbing motions of skilledfirefighters, in an attempt to improve safety andreduce the potential for ergonomically inducedinjuries, namely carpal tunnel syndrome and lowback pain. This study provided an opportunityto capture the experienced firefighter’s knowledgeand use that knowledge to help train new andless experienced firefighters.

Carpal Tunnel SyndromeCarpal tunnel syndrome is a type of cumulativetrauma disorder associated with repeated,sometimes forceful movements involving the wristor arm. The anatomy of the wrist is comparableto a narrow tunnel of bones and ligaments, withthe median nerve passing through. Sometimesthis tunnel becomes “more narrow and pressureis applied to the median nerve, the softestcomponent. This pressure on the median nerveis indicated by the symptoms of tingling, at timespainful sensations in the hands. Complaints alsoinclude changes in sensation, loss of power orstrength with a decrease in the ability to squeeze

or pick up objects with fingers. The carpal tunnelmay become more narrow due to: ligamentsbecoming thicker and sticky due to normal wearand tear from repetitive motion or aging; healedbones from an old fracture protrude into thetunnel; bones getting thicker from arthritis; orfluid retention in tissues, in the carpal tunnel.Because carpal tunnel syndrome is cumulative,workers do not notice damage for months, evenyears” (9). See figure 2.

The Director of Biomedical and BehavioralScience for the National Institute for OccupationalSafety and Health (NIOSH) providedCongressional Testimony regarding health hazardevaluations indicating that job tasks “involvinghighly repetitive manual acts, or necessitatingwrist bending or other stressful wrist postures,are connected with incidents of carpal tunnelsyndrome or related problems. Moreover, it isapparent that this hazard is not confined to asingle industry or job but occurs in manyoccupations. The factor common in these jobsis the repetitive use of hand tools (10).

In the same Congressional Testimony,recommendations for “controlling carpal w:nnelsyndrome have focused on ways to relieveexcessive wrist deviations and arm and handmovements requiring force. Some of NIOSH’srecommendations involve redesign of tools ortool handles, to enable the users wrist to maintaina more natural hand position and to ensure betterdistribution of grip forces during work. Still otherremedial approaches include altering the existingmethod for performing the job task, providingmore frequent rest breaks, and rotating workersacross jobs. Tool and processes redesign arepreferable to administrative means, such as jobrotation, as a first means of prevention” (10).Subsequently, it follows that firefighters canreduce the potential for carpal tunnel syndromeby using the best particular work method for eachfire tool, frequent rest breaks, rotating toolsacross firefighters, and holding the tool with a

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more natural hand position with good grippingaction. These are especially important for Type IIcrews who are not typically work hardened asmuch as Type I IHC crews.

The parameters that best describe body position,tool swing technique and forces associated withrepetitive motions related to carpal tunnel syndromewere determined to be the wrist and elbow rangeof motion, joint angular velocity profiles, peak angularvelocities, motion cycle time, tool lift height, toolhead path, tool acceleration on impact, positionrelative to fireline, and tool stroke rate.

Low Back PainThe exact origin of low back pain is not wellunderstood. There is no strong correlation amongweight, height, stature, and the incidence of lowback pain (11,12). However, there are reportsthat indicate that factors such as physical fitness,abdominal muscle strength, trunk muscle

balance, exposure to heavy lifting or vibration,and even cigarette smoking, are positivelycorrelated to episodes of low back pain (11,12).Other personal factors such as fatigue, posturalstress, trauma, emotional stresses, degenerativechanges, congenital defects, genetic factors, andneurologic dysfunction and body awarenessshould also be evaluated (13). Research showsa strong correlation between low back injuriesand occupations requiring:

• Repetitive or forceful lifting, pushing orpulling

• Repetitive or forceful bending

• Repetitive or forceful twisting

• Awkward postures

• Asymmetrical loading of the spine (e.g., onehanded exertions), and

• Exposure to low frequency vibration (14).

Figure 2—Anatomy of carpal tunnel (10).

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Research on low back pain has progressedbeyond identifying risk factors to include dynamicand three dimensional modeling to evaluate stresspatterns induced during manual lifting; and todetermine how to decrease the stresses throughvarying different load factors or liftingtechniques (13).

Varying load factors and lift techniques are bestdescribed by the arm reach, weight of the tool,body position, and tool swing technique. The armreach necessary to lift or lower a tool is animportant factor in the amount of moment/loadtranslated to the lower back. This load iscomprised of the distance of the tool in the handto the back muscles, multiplied by the weight ofthe tool. The longer the arm reach, the longerthe moment arm, the greater the load, the greaterthe incident of low back fatigue, and the greaterthe incident of low back strain and injury.Consequently, the location of the tool relativeto the operator ’s body is critical in low back strain.The shorter the arm reach the better. Figures 3aand b provide examples of a static two-dimensional biomechanical model, where (M)represents the force produced by the muscle (14).

(a) (b) (c)Figure 3a—Force diagram of stresses/moment

on low back (14).

Carrying loads by using both hands and bybringing the loads closer to the midline of thebody are effective in reducing requiredmusculoskeletal forces (15).

Figure 3b—Force diagram of stresses/moment onlow back (14).

The body positions and tool swing techniquesthat best describe motions and forces from theuse of five hand tools, associated with low backstrain were determined to be left and rightshoulder joint angle profiles, joint angular velocityprofiles, peak angular velocities, body postureat maximum tool lift height and tool impact, toollift height, tool head path, tool acceleration onimpact, and position relative to fireline.

ERGONOMIC FACTORS

Grip StrengthGrip strength and physical fitness are importantergonomic factors to consider in evaluating theuse of fire hand tools. Grip strength is influencedby several factors, including wrist position, handtool configuration and the use of gloves. Gripstrength is greatest when the wrist is straight(pistol type grip). When the hand moves awayfrom that posture, stress increases on the nervesand tendons entering the hand. When the wristis bent (right-angle grip) and force applied,cumulative trauma can result. See figure 4 (16).

(e)(d)

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Another factor that influences the amount ofpower grip strength available is the type of glovesworn. Gloves without seams between the fingersinterfere the least with grip force development.Thick gloves with seams can reduce grip strengthup to 40 percent.

A loss of grip strength while wearing gloves maylead to negative consequences, includingdropping the tool, poorer control of the tool, lowerquality of work, and increased fatigue (18).

Fire hand tools are, by design, right-angled toolsused in a power grip. Consequently, a high gripstrength and gloves with a good fit are importantto providing adequate counter forces to right-angle fire hand tools in a power grip. Grip strengthcan be increased with the use of spring-loadedhand strengthening devices. It is important towear properly sized gloves. Use standard issue,heavy-duty leather gloves manufactured inaccordance with USDA Forest ServiceSpecification 6170-5. Tighten the wrist strap onthe gloves for best fit. Replace gloves as soonas needed.

Physical FitnessA considerable amount of scientific research hasbeen conducted supporting the position thatfirefighting is one of the most physically andmentally demanding occupations. The levels ofmuscular and aerobic fitness are critical tofirefighter performance and the potential foraccidents or injury. Muscular fitness is definedas the level of strength and muscular endurance.Aerobic fitness is the ability or efficiency of thebody to take in and deliver oxygen to the musclesduring arduous activity at a sustainable rate overthe workday. A minimum performance standardbased on physical requirements of the job iscrucial to safety.

Figure 4—The distance, d, between the location wheretool is held in the hand and location where force, F, is

exerted; is less for a typical pistol-shaped tool than for atypical right-angle tool (17).

Stress to the wrist increases as the wrist angleincreases because the force necessary to gripa right-angle tool is higher than compared to apistol shaped tool. In addition, there is a greatertendency for a right-angle tool to twist out ofthe hand than for a pistol type tool. Seefigure 4 (16).

However, Riley, et al, have shown that, in somecases, gloves increase the force that can beexerted to keep objects from rotating or slidingout of the hand. The effect of gloves on tool forcerequirements probably depends on whether forceis required to actively squeeze the tool or topassively resist the twisting and sliding of thetool (17).

MF

d

M

F d

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Studies of firefighting and other field tasks confirmthe link between fitness and work performance.Fit workers perform better in the heat. Theyacclimate faster and work with a lower heart rateand body temperature. They lose acclimatizationslower and regain it faster. Fit workers cope betterwith and recover from adverse firefightingconditions like long shifts and reduced sleep andrest. The physically fit employee misses fewerdays of work because of illness or injury.

Even fit, well-rested firefighters will tire too quicklywhen they work inefficiently. Inefficiency wastesenergy. New workers can be inefficient until theyget instruction and practice in hand tool use.Veteran firefighters are inefficient when saddledwith the wrong fire tools for the job. The righttool can minimize fatigue and energy expenditure.

Fitness is the most important factor in predictingwork capacity. Work capacity is the ability toaccomplish production goals without unduefatigue, and without becoming a safety hazardto yourself or coworkers. Many Federal and Stateagencies have used the step test to predictaerobic fitness. Fitness can’t be rushed and isa gradual process. Depending on the presentfitness, a firefighter may need 6 weeks or moreof exercise to shape up. That is why prudentworkers get into shape before the season begins.They do not work themselves into condition onthe fireline (19). Achieving and maintaining fitnessand work capacity are well described in theNational Wildfire Coordinating Group publication“Fitness and Work Capacity” (20).

Work capacity is the best indicator of the physicalrequirements of wildland firefighting. A precisemethod to measure work capacity is importantto safety, by the way of setting a minimum physicalperformance standard. Currently, the mostprecise method of determining work capacity isthe pack test. Transitioning the pack test toreplace the step test as an indicator of workcapacity is in progress.

BIOMECHANICAL TEST PARAMETERSBiomechanical parameters associated with carpaltunnel syndrome, low back pain, and relatedproblems in wildland firefighters were determined.Body position and tool swing technique were bestdescribed in terms of the use of leg and trunkmuscles, arm and shoulder muscles, bendoverangle, tool stroke rate, tool lift height, distancethe hands are separated when using the tool,position of feet relative to the fireline, and armreach and shoulder angle. These biomechanicaltest parameters are left and right shoulder jointangle profiles, wrist range of motion, joint angularvelocity profiles, peak angular velocities, bodyposture at maximum tool lift height and toolimpact, motion cycle time, tool lift height, toolhead path, tool acceleration on impact, positionrelative to fireline, and tool stroke rate. Fieldtesting was developed around these parameters.

The original fire tool experimental design matrixdeveloped by SDTDC for a series of successivestudies was again utilized, to facilitate theexperimental protocol process and data collectionefforts. This design matrix is included asappendix B. A biomechanics design matrix toevaluate human/tool kinematics for field testingwas developed and followed. This biomechanicstest matrix is included in appendix C.

TEST PROCEDURE ANDINSTRUMENTATIONTwenty-two firefighters grubbed light fuels to baresoil consisting of decomposed granite at a sitewith minimal slope using three test tools, thestandard and Super Pulaskis and the Combi tool.

A magnetic transmitter/receiver system was usedto collect high-speed dynamic data. This system,manufactured by Skill Technologies, Inc,model 6D Research, serial number 82451, useslow frequency magnetic technology to tracksensors placed within a magnetic field createdby a source. Firefighters were outfitted with

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biomechanical sensing equipment, consisting of a transmitterand eight position/angle sensors mounted on sevendesignated body segments and the tool handle. These eightsensors were cabled to a computer with software capableof recording translational and rotational movement on a rapidbasis at 30 hertz. These multiple measurements were takento provide improved statistics and increased accuracy inbiomechanical measurements.

This magnetic sensor system was initially calibrated in orderto determine the exact position and orientation of each bodysensor. Kinematics were derived from position data, (x, y, z)to include linear and angular velocity, linear and angularacceleration. Tool head position data were obtained, andvelocity and acceleration values were derived.

The heart rate was used as a physiological indicator of energyexpenditure and was continuously monitored. The heart ratemonitor was manufactured by Polaris Inc., model Pulsar II,serial number 431047. In a previous study test workers,grubbing at a rate for indirect line, had a heart rate of140 to 150 beats per minute. Monitoring apparatus consistedof a transmitter positioned over the lower chest and a receivertaped to the hard hat (3). See figure 5.

Figure 5—Heart rate and monitoring apparatus.

Test workers completed a preferencerating of hand tools based onsubjective responses/opinions oncompletion of biomechanical testing.This rating is included as appendix D.A detailed description of the testprocedure may be found in the “USDAFire Tool Ergonomics Testing ofHuman Kinematics” test planApril 1997 and August 1998 (7).

Test ToolsThe fire hand tools tested were thestandard Pulaski, the Super Pulaski,and the Combi tool. These tools areshown in figure 6. Physicalcharacteristics are indicated intable 1. Tool selection criteria werebased on information extracted fromIHC respondents to the aforementioned

Figure 6—Test tools of the Combi tool,standard Pulaski, and Super Pulaski.

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Table 1—Test Tool Configurations

fire tool survey (3). The Combi tool was includedas the reference grubbing tool for comparisonbased on high productivity rates determined bythe MTDC tool study in 1988. Each of the testtools was sharpened, as appropriate, to astandard sharpness and angle for scraping priorto use. The tools were archived as reference toolsfor further testing.

The standard Pulaski and Combi tool aremanufactured in accordance with the minimumrequ i rements o f Fores t Serv iceSpec i f i ca t ions 5100-355 and 5100-325respectively. The Super Pulaski used in this testwas a field modification consisting of a standardPulaski with an additional standard Pulaski hoeblade, cut into two pieces and welded onto thebasic hoe, half on either side.

There are several variations of the Super Pulaskicurrently being used in the field by IHCfirefighters. Their design ranges from the weldeddouble hoe used in this test, to a more refineddesign of a wide hoe blade fabricated as onepiece via a sand casting, with a decreased weight,smaller hoe blade, and no weld lines present.Based on a comparative analysis of the fieldmodifications and commercially available SuperPulaski configurations, the heaviest doublewelded hoe design of the Super Pulaski wasselected due to the expected severe application.

Preparation for TestingTest workers were outfitted in full PPE and gear.Fire shelters were removed from the carryingcase and replaced with practice shelters, becausethe fire shelters contain a ferric-based metal thatinterfered with the magnetic motion sensorsystem. Two full water canteens were included.A fully equipped test worker is shown in figure 7.

Figure 7—A test worker in full gear and PPE.

Handle HoeTool Length Handle Weight Width Weight/Width

Number Tool Head Type Inches Material Pounds Inches Pounds/inch

1 Standard Pulaski 34.5 Wood 5.4 3.0 1.6

2 Super Pulaski 34.5 Wood 6.9 6.8 1.0

3 Combi Tool 40.0 Wood 4.6 4.0 1.2

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Each test worker was fullyinstrumented prior to testing. Inaddition, each worker was briefedon what was to be accomplishedduring the test procedure. Theinstructions on how testing wasconducted were the same for eachtest worker.

The test site consisted of minimalslope, decomposed granite and lightfuels. Heavier roots were removedprior to testing to maintain a lightuniform fuel. Removal was minimal.A fireline quality of grubbing to baresoil was monitored and standardizedas much as practicable.

The heart rate was used as aphysiological indicator of energyexpenditure. Consequently, the testworkers in this study were coachedto speed up or slow down grubbingin relation to the desired heat rate.Monitoring apparatus consisted ofa transmitter strapped around thelower chest and positioned withoutrestricting normal upper bodymovement. The heart rate receiverwas taped to the top of the hard hatin a position readily visible to thetest engineer, when the worker wasin the grubbing position.

The biomechanics sensor systemwas configured to determine left andright shoulder joint angle profiles,wrist range of motion, joint angularvelocity profiles, peak angularvelocities, body posture at maximumtool lift height and tool impact,motion cycle time, tool lift height,tool head path, tool acceleration onimpact, position relative to firelineand tool stroke rate.

Test workers were instrumented with seven sensors immediatelyprior to testing. An eighth sensor was mounted on the handleof the tool to be tested, near the head. The tool head consistedof a ferrous-based metal and interfered with the magnetic motionsensor system. Consequently, the tool sensor was positionedapproximately 4 inches down the handle. This dimension fortool sensor placement on the handle was used as a correctionfor the tool head data. See figure 8.

Figure 8—Position/angle sensor mounted on the tool head.

Test workers had a 3-minute warm-up period of grubbing witheach test tool, for a total of approximately 5 minutes of grubbingper tool.

Detailed Test MethodInstrumented test workers warmed-up for 3 minutes by diggingsimulated fire line. They were coached to either increase orslow the rate of grubbing to bring the heart rate to130 to 140 beats per minute. After 3 minutes, the worker movedto the test course and was positioned in front of the systemrece iver fo r sys tem ca l ib ra t ion . Ca l ib ra t ion took10 to 15 seconds.

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The test worker was instructed to begin grubbing in thetest course, making a trench about 12-inches wide and 2-inches deep. Grubbing techniques were monitored andstandardized as much as practicable. Grubbing wasperformed within a range of 12 feet from the magneticsystem transmitter. See figure 9.

Figure 9—Test worker grubbing in the test course.

The Project Leader signaled the test crew to begin gatheringdata. Data were collected for a total of 25 strikes or more.

After data collection was completed on a tool, the testworker progressed to the next tool. Tool changeover andtool sensor application took 10 to 15 seconds. The testworker was again positioned in front of the systemtransmitter for calibration before the use of each tool.

Position/angle sensor data were collected via a computer.The magnetic sensors had a sampling rate of 30 Hz or30 cycles per second. Sensor data were stored in an ASCIIfile format, tab delimited and were imported into an Excelspreadsheet for analysis. Testing was videotaped for projectdocumentation. The derived kinematic data were storedon disk for analysis.

Determination of Skilled andRegular FirefightersTool testing was documented withtechnical videotape. This videotape wasv iewed and the Da l ton IHCSuper in tendent and Ass is tan tSuperintendent evaluated skill level.Based on this evaluation the workers/firefighters were categorically grouped,based on skill level in terms of regularversus skilled firefighter. The top sixregular and skilled firefighters wereselected. Gender was mixed for bothskill categories.

DETAILED DATA ANALYSIS BYTOOLAs a result of the continuous datacollection process, multiple cycles ofthe grubbing motion were provided foreach tool and test worker. As a result,the average motion over a number ofcycles, 25 or more, for each worker andtool were determined. The average andstandard deviations for all designatedmotions, for all three tools, for bothregular and skilled groups, weredetermined. Variables of interest werecalculated and a comparative analysiswas performed between the groupaverages and standard deviations foreach tool. Comparison parameterswere:

• Work cycle time (tool stroke rate)

• Tool lift height

• Tool impact acceleration (toolimpact force or gs)

• Tool head path

• Hand separation

• Posture at maximum tool lift height

• Posture at tool strike/impactacceleration

13

• Range of motion, for all joints

• Peak angular velocities, for all joints

• Joint angle profiles, for left and rightshoulder for internal/external rotation,adduction/abduction, and flexion/extension.

• Joint angle profiles, for left and right elbowfor pronation/supination, adduction/abduction, and flexion/extension.

• Joint angle profiles, for left and right wristfor internal/external rotation, ulnar/radialdeviation, and flexion/extension.

• Joint angular velocity profiles, for left andright shoulder for internal/external rotation,adduction/abduction and, flexion/extension.

• Joint angular velocity profiles, for left andright elbow for pronation/supination,adduction/abduction, and flexion/extension

• Joint angular velocity profiles, for left andright wrist for internal/external rotation,ulnar/radial deviation, and flexion/extension.

Data analysis of the most pertinent graphsfollows. All other associated graphs and tablesare provided in appendix E.

Standard PulaskiAn examination of joint angle profiles for thebiomechanics associated with the use of thestandard Pulaski indicates that hand andshoulder position vary significantly betweenregular and skilled workers/firefighters. Regularworkers performed the first half of the motionswith respect to shoulder and hand position similarto that of a skilled worker. However, regularworkers draw the second half of the motion outand perform it much more slowly. See figures 10and 11. Hand separation profiles are very similarbetween regular and skilled workers. The handseparation for regular workers on the averagewas 15 inches, and 16 inches for skilled workers.No obvious differences are evident in the elbow

and wrist joint angle profiles. Angular velocitypeaks did not seem to differ significantlybetween regular and skilled workers. See table F1.

Significant differences in cycle duration, toolimpact force, and lift height were observedbetween regular and skilled workers with theuse of the standard Pulaski. Regular workershad an average cycle duration of 1.1 seconds,55 tool strikes per minute, tool impact forceof 4.5 gs, and lift height of 32 inches. Skilledworkers had an average cycle duration of0.8 seconds, 75 tool strikes per minute, toolimpact force of 2.7 gs, and lift height of20 inches. Skilled workers are 36 percent moreproductive as determined by tool strike basedon the assumption that the grubbingeffectiveness is the same for skilled and regularworkers. This is probably not true and gives abenefit of error in the favor of the regularworker.

Tool head acceleration is best described interms of tool impact and G forces. The G forceis a force of acceleration that pulls on the toolhead. The force of gravity on Earth is used asa baseline for measuring this force ofacceleration. Gs are directly related to theweight of the tool. As the firefighter pulls moregs, the weight of the tool head or G forceincreases correspondingly. The 5.4-poundPulaski has 1 g when motionless, for a G forceof 5.4 pounds. However, the same 5.4-poundstandard Pulaski moving with 4.5 gs will weigh24 pounds when used by regular firefighters.Skilled firefighters typically generate around2.7 gs or 15 pounds G force on impact. Thelower the G force on impact the better.

Regular workers performed two motion cyclesfor every three completed by a skilled worker.See figures 12, 13, and 14. Skilled workerscan complete 75 tool strikes for every 55 bya regular worker, or are 36 percent moreproductive. Using standard hand crew

14

Figure 10—Hand separation, regular workers draw the second half of the motion out.

15

Figure 11—Shoulder position, regular workers draw the second half of the motion out.

16

Figure 12—Work cycle duration.

17

Figure 13—Tool impact force.

18

Figure 14—Tool lift height.

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production rates for medium brush for a line widthof 6 feet, a crewmember can typically average30 feet of line per hour and a 15-person crewcan build approximately 450 feet per hour. Anassumption can be made that half of the creware skilled and the other half are regular workers.A 36 percent increase in productivity can increaseline by 68 feet per hour if the whole crew wastrained to the skilled level. That is comparableto having 2 people added to a 15-person crew.Again, this is based on the assumption that halfthe crew is already skilled.

The standard Pulaski has a 3-inch hoe blade.The regular worker with 55 strikes per minutecan strike/grub 165 inches per minute. The skilledworker with 75 strikes per minute can strike/grub225 inches per minute.

In addition, because a regular worker elevatesthe tool head 50 percent higher than a skilledworker, a regular worker expends the sameamount of energy in two cycles as is expendedby a skilled worker in three cycles, simply bylifting the tool head higher. Furthermore, a regularworker impacts the tool head with nearly twicethe force used by a skilled worker.

Body posture at maximum tool height and toolstrike with the use of the standard Pulaski wasexamined. Positional differences greater than onestandard deviation indicate significant areas forimprovement in regular workers motion.

Body posture at maximum height the standardPulaski is lifted is best described by the rightand left shoulder angles, right hand reach, andleft arm twist. These biomechanical parametersare the angles of right shoulder flexion/extension,left shoulder flexion/extension and adduction/abduction, right elbow flexion/extension, and leftelbow pronation/supination. See table F2. Forthis posture, with one exception, the variabilityin the key angles about the average posture wascomparable, 2 to 5 degrees, for both regular and

skilled workers. However, left elbow adduction/abduction variation was nearly three timesgreater, around ±10 degrees in regular workersas compared to skilled; even though their averageposition was similar, minus 31 degrees in regularworkers and minus 35 degrees in skilled workers.See table F2.

Body posture at tool strike shows an increasednumber of angles indicating differences in anglessimilar to those noted for posture at maximumtool height. The most significant of thesedifferences are in the right and left shoulderflexion/extension and adduction/abductionangles. Other angles of interest are both wristsand left elbow positions. See table F3. Anexamination of the individual angle ranges ofmotion indicates a wide variance between rangeof motions (ROM) between regular and skilledfirefighters, especially in left and right shoulder.See table F4. This is easily observed as regularworkers use arm and shoulder muscles to powerthe tools. In direct contrast, skilled workers areobserved to use leg and trunk muscles mainlyand arm and shoulder muscles sparingly withthe use of the standard Pulaski.

It is clearly evident from the examinations of bodyposture at maximum tool height and tool strike,and ROM, that shoulder position is important indetermining the skill level of a worker using astandard Pulaski.

Key points determined in this kinematic analysisof the use of the standard Pulaski are:

• Regular workers perform the first half ofshoulder and hand separation motionssimilar to that of a skilled worker, but drawout the second half of the motion andperform it much more slowly.

• Regular workers perform two motion cyclesfor every three completed by a skilledworker.

• Regular workers impact the tool head withnearly twice the force used by skilledworkers.

• Regular workers elevate the tool head50 percent higher than a skilled worker.

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• Regular workers expend the same amountof energy in two cycles that is expendedby skilled workers in three cycles, simplyby lifting the tool head higher.

• Shoulder position is important in determiningthe skill level of a worker using a standardPulaski.

• Regular workers use arm and shouldermuscles to grub. Skilled workers use legand trunk muscles. Arm and shouldermuscles are significantly smaller than legand trunk muscles and fatigue quicker.

• Regular workers using the standard Pulaskiwith a 3-inch hoe blade, and 55 strikes perminute can strike/grub 165 inches perminute. Skilled workers with 75 strikes perminute can strike/grub 225 inches perminute.

Super PulaskiAn examination of the joint angle profiles for thebiomechanics associated with the use of theSuper Pulaski reveal patterns similar to thestandard Pulaski. However, these differences aremore pronounced and distributed among a greaternumber of the joints. The right shoulder motionsfor regular and skilled workers follow similarpatterns, with the regular worker drawing themotion out over an even longer duration. Seefigure 11. The elbow pattern differences are thesame as that for the right shoulder. See figures 11and 15. The left shoulder profiles show that agreater range of motion is employed by regularworkers for the left shoulder adduction/abductionand flexion/extension angles. See figures 16and 17.

The wrist angle and velocity profiles with the useof the Super Pulaski are quite interesting. Wristangles are almost unchanged though thecomplete tool swing by the regular worker ascompared to a skilled worker. See figures 18,19, 20, and 21. In general, peak angular velocitiesare higher for skilled workers. See table F1. With

respect to separation of the hands, the regularworker draws their hands together more graduallythan a skilled worker. A skilled worker draws theirhands together very quickly, almost in a snappingaction. Hand separation at the beginning of theup-stroke for regular workers is 10 inches and16 inches for skilled workers. During up-stroke,regular workers quickly widen hand separationfrom 10 inches to 15 inches, while skilled workersmaintain a constant hand separation of 16 inchesuntil the end of up-stroke, when they snap theirhands together quickly early in the down-strokephase. See figure 10.

As with the standard Pulaski, the use of the SuperPulaski provided pronounced differences ingrubbing cycle time, tool impact force, and liftheight. In each of these three parameters, themean value for regular workers was nearly twicethat of the skilled worker. Regular workers hadan average cycle duration of 1.6 seconds,40 strikes per minute, tool impact force of 5.3 gsand lift height of 41 inches. Skilled workers hadan average cycle duration of 0.8 seconds,75 strikes per minute, tool impact force of 2.9 gsand lift height of 23 inches. This means a skilledworker can perform two cycles to every oneperformed by the regular person for a given timeduration and energy expenditure. See figures 12,13, and 14.

Skilled workers can complete 75 tool strikes forevery 40 by a regular worker, or are 88 percentmore productive. Using the same standard handcrew production rates for medium brush for aline width of 6 feet, as described with the standardPulaski. An 88 percent increase in productivitycan increase line by 136 feet per hour if the wholecrew was trained to the skilled level. That iscomparable to having 4 people added to a 15-person crew. Again, this is based on theassumption that half the crew is already skilled.However, previous fire tool studies have proventhat the increased energy cost far out weighsany production gain.

21

Figure 15—Right elbow flexion/extension angle.

22

Figure 16—Left shoulder adduction/abduction angle.

23

Figure 17—Left shoulder flexion/extension angle.

24

Figure 18—Right wrist flexion/extension angle.

25

Figure 19—Right wrist flexion/extension angular velocity.

26

Figure 20—Left wrist flexion/extension angle.

27

Figure 21—Left wrist flexion/extension angular velocity.

28

The Super Pulaski has a 6.8-inch hoe blade. Theregular worker with 40 strikes per minute canstrike/grub 272 inches per minute. The skilledworker with 75 strikes per minute can strike/grub510 inches per minute.

The same body postures at maximum tool heightand tool strike, and the same key angles wereexamined for the Super Pulaski that wereevaluated for the standard Pulaski. Variabilityof these body postures was similar,3 to 6 degrees between groups. See tables F2and F3.

In general, the full ranges of motions were largerfor regular workers with the use of a SuperPulaski, as compared to skilled workers. Seetable F4. As with the standard Pulaski, this iseasily observed as regular workers used armand shoulder muscles for grubbing; and skilledworkers used leg and trunk muscles mainly forgrubbing.

Based on the examination of body postures atmaximum tool height and tool strike, the shoulderposition and wrist angle are important indetermining the skill level of a worker using aSuper Pulaski.

Key points determined in this kinematic analysisof the use of the Super Pulaski are:

• The biomechanic values measured in thejoint angle profiles with the Super Pulaski,reveal patterns similar to the StandardPulaski, except that differences betweenregular and skilled workers are morepronounced and distributed among a greaternumber of the joints.

• Regular workers perform the first half of themotion similar to that of a skilled worker anddraw the second half of the motion out andperform it much more slowly, even longerthan with the standard Pulaski.

• Regular workers perform one motion cyclefor every two completed by a skilled worker.

• Regular workers impact the tool head withtwice the force used by skilled workers.

• Regular workers elevate the tool head100 percent higher than a skilled worker.

• Regular workers expend the same amountof energy in one cycle that is expended bya skilled worker in two cycles, simply by liftingthe tool head higher.

• The full range of motions was larger forregular workers as compared to skilledworkers.

• Shoulder position and wrist angle areimportant in determining the skill level of aworker using a Super Pulaski.

• As with the standard Pulaski, regular workersused arm and shoulder muscles for grubbing;skilled workers used leg and trunk musclesfor grubbing. Consequently regular workersare expected to fatigue much more quicklydue to the size difference of these muscles.

• The Super Pulaski has a 6.8-inch hoe blade.The regular worker with 40 strikes per minutecan strike/grub 272 inches per minute. Theskilled worker with 75 strikes per minute canstrike/grub 510 inches per minute.

• Previous fire tool studies have shown thatthe increased energy costs far out weightany production gain.

Combi ToolThe joint angle profiles of regular and skilledworkers are the most similar for use of the Combitool, when compared with the standard and SuperPulaskis.

This indicates that the Combi tool wouldbe the easiest tool to train regularfirefighters to become skilled firefighters.See figures 11 and 15.

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Left and right shoulder angle profiles are similarfor regular and skilled workers with the use ofthe Combi tool, except that the flexion/extensionrange of motion was larger for regular workers.See figures 16, 17, and 22 for the left shoulderand figures 11, 23, and 24 for the right shoulder.The joint angle profiles for the right elbow andwrist, and left elbow and wrist are similar, exceptfor the right wrist flexion/extension angle. Seefigures 15 and 25 for the elbows and figures 18and 19 for the wrists. The right wrist flexion/extension profile for a regular worker is almosta mirror image of the profile for a skilled worker.Peak angular velocities are generally higher inregular workers, with the largest differences seenin the left wrist and elbow. See table F1 andfigures 20 and 21. The hand separation forregular workers on the average was 16 inches,and 23 inches for skilled workers. See figure 10.

Although there are only minor differences in thejoint angle profiles between regular and skilledworkers, there are significant differences inmotion cycle time, tool impact force, and toollift height. See figures 6, 7, and 8. Regularworkers had an average cycle duration of0.9 seconds, 67 tool strikes per minute, toolimpact force of 3.0 gs, and lift height of 21 inches.Skilled workers had an average cycle durationof 0.7 seconds, 86 strikes per minute, tool impactforce of 1.8 gs, and lift height of 12 inches. Toolimpact force and lift height for regular workersare approximately 70 percent greater than skilledworkers. In addition, regular workers require anaverage of 40 percent more time to complete agrubbing cycle, as compared to skilled workers.The lift height used by skilled workers isapproximately 12 inches.

This does not seem intuitive until theadditional length of the Combi handle isconsidered. This is the lowest energy costof the tools tested.

Skilled workers can complete 86 tool strikes forevery 67 by a regular worker, or an increase of

28 percent in productivity. The same standardhand crew production rates for medium brushfor a line width of 6 feet as described with thestandard Pulaski were used. A 28 percentincrease in productivity can increase line by55 feet per hour if the whole crew was trainedto the skilled level. That is comparable to having2 people added to a 15-person crew. Again, thisis based on the assumption that half the crew isalready skilled. It is important to note than thetool strike/grub rate for the Combi tool for regularworkers is high compared to values reported forthe standard Pulaski and Super Pulaski.Consequently, the difference between regular andskilled worker with the Combi tool is bestdescribed by taking into account the blade widthversus strike rate, as follows.

The Combi tool has a 4-inch serrated blade. Theregular worker with 67 strikes per minute canstrike/grub 268 inches per minute. The skilledworker with 86 strikes per minute can strike/grub344 inches per minute. The Combi tool is themost efficient tool based on the low energy cost,high productivity, and safety aspects, especiallyfor the regular firefighter.

Body posture at maximum lift height and toolstrike with the use of the Combi tool did not varyto the same level of differences between regularand skilled workers, as observed with thestandard and Super Pulaskis. See tables F2and F3. This indicates the Combi tool is a bettertool for regular firefighters as skills are developed.

Body position at the maximum tool lift height hadslightly more variability, with 3 to 7 degrees forregular workers and 2 to 4 degrees for skilledworkers. A 7-degree variation of regular rightshoulder flexion/extension angle is relatively largein comparison to the other levels of variability.Body position at tool strike indicated a similarvariability of 3 to 5 degrees for regular and skilledworkers.

30

Figure 22—Left shoulder adduction/abduction angle.

31

Figure 23—Right shoulder adduction/abduction angle.

32

Figure 24—Right shoulder flexion/extension angle.

33

Figure 25—Left elbow flexion/extension angle.

34

Regular workers continued to be observed usingarm and shoulder muscles for grubbing with theCombi tool, but were also observed using someleg and trunk muscles. The skilled workerscontinued using leg and trunk muscles forgrubbing with the Combi tool. Consequently,regular workers are expected to fatigue quickerwith the standard and Super Pulaski whencompared to the Combi tool.

This further substantiates that the Combitool is the most efficient tool for regularfirefighters as skills are developed.

Based on the examination of body posture atmaximum tool height and tool strike, the shoulderposition is important in determining the skill levelof a worker using a Combi tool.

Key points determined in this analysis of the useof the Combi tool are:

• Joint angle profiles of regular and skilledworkers are the most similar for use of theCombi tool, as compared to the standardand Super Pulaskis.

• Left and right shoulder angle profiles aresimilar for regular and skilled workers, exceptthat the flexion/extension range of motionwas larger for regular workers

• The right wrist flexion/extension profile fora regular worker is almost a mirror imageof the profile for a skilled worker.

• Peak angular velocities are generally higherin regular workers, with the largestdifferences seen in the left wrist and elbow.

• Hand separation profiles are very similarbetween regular and skilled workers.

• Regular workers perform the first half of handseparation and right shoulder motion similarto that of a skilled worker, drawing thesecond half of the motion out and performingit more slowly.

• Regular workers perform two motion cyclesfor every three completed by a skilled worker.

• Regular workers impact the tool head with70 percent more force than skilled workers.

• Regular workers elevate the tool head70 percent higher than a skilled worker.

• Regular workers expend the same amountof energy in three cycles that is expendedby a skilled worker in two cycles, simply bylifting the tool head higher.

• Body posture at maximum lift height andtool strike did not vary to the same level ofdifferences between regular and skilledworkers, with the standard and SuperPulaskis.

• Shoulder position is important in determiningthe skill level of a worker using a Combitool.

• The Combi tool is a better tool for regularfirefighters as skills are developed.

• Regular workers are expected to fatiguequicker with the standard and Super Pulaskias compared to the Combi tool.

• The Combi tool has a 4-inch blade. Theregular worker with 67 strikes per minutecan strike/grub 268 inches per minute. Theskilled worker with 86 strikes per minute canstrike/grub 344 inches per minute.

• The Combi tool is the most efficient toolbased on the low energy cost, highproductivity, and safety aspects, especiallyfor the regular firefighter.

DETAILED DATA ANALYSIS BYBIOMECHANICAL PARAMETEROverall the skilled workers generated smoother,more consistent motions for the entire group overthe entire cycle of motion. Conversely, regularworkers had more variation in the motion for theentire group over the entire cycle. Plus or minusa standard deviation is a measure of the variationfrom the average motion for the group. See

35

figures 10 through 25, and appendixes E and F.Typically, the standard deviation is wider forregular than for skilled workers across allbiomechanical parameters measured. Generally,biomechanical analyses reveal that a group ofskilled workers performs a task more consistently,i.e., the standard deviation is significantly smallerthan a group of regular workers performing thesame motion.

Tool Acceleration/Force At ImpactWith respect to tool acceleration at impact, ameasure that is equivalent to force, both groupsmaintain a consistent impact force per pound oftool with the regular worker impact force nearly145 percent that of the skilled worker. Seefigure 10. This is partially due to the increasedlift height and the increased angular velocityresulting from the extended reach of regularworkers. See figures 3 and 14. This is going tocause increased work on the back for tworeasons. First, back exertion will be required tosupport the motion. Secondly, the tool will beburied further into the ground causing more strainon the back to free the tool blade to completethe motion cycle. See figure 26.

Figure 26—Increased work from increased lift andextended reach by regular workers.

Key points determined in this kinematics analysisof the tool acceleration/force at impact are:

• The average impact force for all tools,delivered by the regular worker is nearly145 percent that of the skilled worker.

• This is partially due to the increased liftheight and the extended reach of regularworkers, increasing the potential for backstrain.

Tool Lift HeightTool lift height is another factor contributingsignificantly to an increased regular cycle time.Interestingly, the heavier the tool, the higher theregular worker lifted the tool. See table 1 andfigure 14. On the other hand, the skilled workerdecreases the height for an increased tool weight.

Compare the lift height graphs for the three tools.This gets back to the use of momentum andgravity. Skilled workers appear to use the sameamount of power regardless of tool weight. Thiscan be considered pacing, in order to maintaina sustainable work rate. Skilled workers maybe working at maximum energy output, so theyvary technique to maintain constant power output.Skilled workers vary lift height according to toolweight, less lift for more given weight. This isdue to gravity contributing more significantly tothe motion, in terms of momentum, due to anincreased weight. Consequently, it follows thatregular workers should start learning with alighter tool until control of power andtechnique are learned, then progress toheavier tools.

Key points determined in this kinematic analysisof tool lift height are:

• Regular workers lift the tool 50 percent,100 percent, and 70 percent higher thanskilled workers for the standard Pulaski,Super Pulaski, and Combi tool respectively.

• The higher the tool lift, typically the longerthe cycle time.

36

• The heavier the tool, the higher the regularworker lifted the tool.

• The heavier the tool, the lower the skilledworker lifted the tool.

• Skilled workers appear to use the sameamount of power regardless of tool weight.

• Regular workers should start learning witha lighter tool until control of power andtechnique are learned, then progress toheavier tools.

Work Cycle TimeSkilled workers keep the work cycle time nearlythe same, regardless of handle length or toolweight. Skilled workers keep the energy levelrequired to perform a motion uniform, resultingin a sustainable work rate. In other words, skilledworkers know how to pace themselves basedon the tool, for all tools. Regular workers do notappear to pace themselves. This may be thereason for reports that they fatigue more quicklyand severely with increased tool weight. This alsocauses the regular worker to require a longerrecovery time. When the regular worker lifts aheavier tool higher, the tool comes down with agreater force, due to the increased verticaldistance and increased mass. The regular workeruses greater care in hand position, contributingto increased energy requirements and cycle time.Because of this, regular workers bury the toolblade into the soil further than skilled workers,making it necessary to jerk the tool from the soil,further compounding the energy needs for thetask. The consistency of skilled cycle time andincreased regular cycle time is illustrated infigure 10.

Tool Head Path—Position and displacementgraph of the path of travel of the tool head. Seefigures 27 and 28.

Hand SeparationHand separation performance graphs for thestandard Pulaski indicate that regular and skilledworkers begin the motion with their hands in thesame position. However, skilled workers pull their

hands together much faster than regular workersas they bring the tool in a down swing.

It appears that skilled workers are using onepower generating arm/hand and one guidinghand. The regular workers appear to separatepower generation from tool guidance. By havingtool guidance in a second phase, the regularworker does not take advantage of the tool’snatural momentum from the pull of gravity. As aresult, regular workers are “fighting” the naturalfall of the tool, increasing the workload. Regularworkers start in the same position, but use bothhands to control the tool path throughout thecomplete swing, causing the cycle time to beprolonged.

A comparison of hand separation graphs for thestandard Pulaski, Super Pulaski, and Combi toolsindicates that this is a weight dependant issue.See table 1 and figure 10. The lighter the tooland the longer the handle, the further apart skilledworkers positioned their hands. The oppositeis true of regular workers, especially in the lasthalf of the motion. Skilled workers snap theirhands together. Regular workers gradually pulltheir hands together slowly, in order to maintaingreater control over the tool head. An examinationof the skilled standard deviation during the firsthalf of the motion shows that heavier tools requiregreater consistency of motion. This is one ofthe factors contributing to increased cycle time.

Wrist Rotation Joint Angle ProfileRecall that the area under the joint angle curvesis a measure of the energy exerted during themotion. For example, the area under all jointprofile curves is much greater for regular workersthan for skilled workers across all biomechanicalparameters measured. See figures 10through 25, and appendixes E and F.

This increased energy input and lack of toolcontrol by regular workers, specifically with the

37

Figure 27—Standard Pulaski tool head path, regular workers.

38

Figure 28—Standard Pulaski tool head path, skilled workers.

39

Super Pulaski, causes a safety concern. This isillustrated by the bandwidths and irregularity ofperformance graphs for regular workers. TheSuper Pulaski is typically a non-scientific fieldmodification of the standard Pulaski, with anincrease in mass on the hoe blade, with noapparent design consideration given for theresultant change in the dynamics/tool balancecaused by this increase in mass. When one bladeof a dual tool head is changed, the entire toolhead needs to be redesigned/re-balanced to keepthe center of gravity and center of percussionalong the tool handle centerline (3). For the SuperPulaski, the increase in mass on the hoe bladehas moved the center of gravity and center ofpercussion further away from the handlecenterline as compared to the standard Pulaski.Consequently, the angular acceleration increases,causing an increased impact rotation. This issensed by the firefighter as increased handletwist on impact, stinging hands and increasedonset of fatigue. Furthermore, changing the toolhead mass on the hoe side without balancingthe entire tool head may affect the proper useof the chopping blade by creating choppinglimitations, again, compromising safety.

Regular and skilled workers react to this twistingforce differently. These differences are evidentin the right wrist internal-external rotation jointangle profiles. The graph for the standard Pulaski,a nearly balanced tool head, shows that bothskilled and regular workers utilize wrist internal-external rotation similarly. However, the SuperPulaski curve is quite different so far as theregular worker is concerned. The skilled workerduplicates the standard Pulaski motion with aslight increase in rotation to compensate for theimbalance, while the regular worker allows thetool to twist by providing no resistance via wristrotation. See figure 29.

The increase in tool head weight of the SuperPulaski does increase wrist rotation throughoutall cycles for skilled workers. However, regularworkers allow the Super Pulaski to freely rotatethrough the whole cycle. This is a critical safety

concern. The regular worker has a freely rotating,sharp edged Super Pulaski, impelled by aconsiderable amount of momentum directed withthe tool blade angled toward the non-dominantfoot. See figure 30. A time lost accident studyto evaluate this safety concern is prudent.Firefighters have noted an increase in toolrotation on impact and this may be a strongcontributing factor. Further study is warrantedregarding lost time accident studies and workercompensation for carpal tunnel and low backinjuries associated with the use of fire hand tools.Furthermore, a study to determine the optimumhoe blade width for a balanced Pulaski usingrigorous scientific methodology would be prudentand cost effective from a production and safetyperspective.

Shoulder Flexion/extension Angle and ArmReachExamination of the right shoulder flexion/extension angle shows a regular worker increasesarm reach. See figures 10 and 24. Thesignificance of increased reach is an increasedloading of the lower back, which translates toearlier fatigue of the lower back, increasing thepotential for back injury. Regular workers startthe grub motion cycle with the right shoulderflexion/extension angle at 22-degrees open forthe standard and Super Pulaski and 12-degreesopen for the Combi tool. By contrast, skilledworkers start uniformly at around 6-degrees openfor all tools. The regular worker increases theright shoulder flexion/extension angle by18 degrees and the skilled worker by 34 degreeswith the standard Pulaski. Regular and skilledworkers both increase the angle by 40 degreeswith the Super Pulaski. Interestingly, regularworkers increase the angle by 40 degrees withthe Combi tool, as compared to skilled workersincreasing by 24 degrees. This may be due tothe regular worker using only arm and shouldermuscles with the standard and Super Pulaskiand adding the use of leg and trunk muscleswith the use of the Combi tool only. Skilledworkers predominantly use only leg and trunkmuscles for all tools.

40

Figure 29—Standard Pulaski, Super Pulaski, and Combi Tool—Right wrist internal external rotation.

41

• Regular workers typically have the non-dominantfoot slightly forward and intersecting the tool path.

• The knees are flexed and the back may or maynot be straight.

• The regular worker is bent at the waist andback not parallel to the ground; more upright.

• There is an up and down, bobbing motion ofthe back. Arm and shoulder muscles are usedfor grubbing.

• The tool blade is angled towards the non-dominant foot in the tool swing path. However,the tool swing stops short of the foot.

• The increased arm reach of the regular workermay also be a method of compensating for thedifference in body posture relative to the fireline as compared to the skilled worker.

Figure 30—Regular worker body posture andtool swing path.

• Skilled workers tend to have the dominant footslightly forward and essentially parallel to thetool path; non-dominant foot 60 degrees off thedominant foot.

• Knees flexed; back straight; bent at the waistat an angle almost parallel to the ground;

• The tool blade angled away from the body, withfeet positioned out of the way of the swing ofthe tool blade.

• During the tool swing, back position is keptalmost steady.

• Uses leg and trunk muscles for grubbing. Seefigure 31.

Figure 31—Skilled worker body posture andtool swing path.

REGULAR WORKER SKILLED WORKER

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

42

Proposed Training ProgramSkill development is achieved through instructionand practice. A practical training program ensuresgreater success of implementation. The followingtraining has been developed to implement thefive principle factors of skilled grubbing and theprimary use of leg and trunk muscles: tool liftheight, work cycle time, hand separation, rightshoulder angle and position of feet. Train to theseprinciples one step at a time. It is important tofully master each principle before moving to thenext principle. Start with the Combi tool andprogress to the standard Pulaski when the workeris skilled at the use of the Combi tool.

This training program requires further refine-ment, including results verification, beforeimplementation.

Position of Feet Relative to Fireline—Positioning of feet in the skilled worker postureas described in figure 31.

Tool Lift Height—Obtain three wooden stakesand brightly colored wooden dowels, rulers orsticks. Mark off 3 inches from the bottom tip ofthe first stake with a permanent marker. Write“ground” just below the mark. Pound the stakeinto the ground until the word “ground” can nolonger be seen. Measure 20 inches above theground mark and mark this level “Pulaski”. Securea colored dowel at this point, perpendicular tothe stake. See figure 32. Repeat the procedurewith the other 2 stakes and colored dowels,except use 23 inches for the Super Pulaski and12 inches for the Combi tool. An alternativemethod would be to use flagging, tied to the toolhead at the handle, measured to the properlength, with a wad of flagging added to the endto add a little weight. String or cord could alsobe used with the same method. These materialsare readily available at fire camp, and could beused to alert regular firefighters to the propertool lift height.

This positioning combined with the differencein hand separation contributes to the drasticdifference observed in left shoulder flexion/extension in the Super Pulaski. See figure 17.The regular worker has the front, non-dominanthand further down the tool handle as the bladedrops. Again increasing the loading on the lowerback because the regular worker is stretchedout and more stooped over. See figures 22, 23,and 24.

Critical Biomechanical ParametersBased on the results of the comparative analysis,a determination was made that there are fivecontrolling parameters that describe the optimumbody position and tool swing technique, usingprimarily leg and trunk muscles for the skilleduse of fire hand tools. Furthermore, all otherparameters discussed will fall in line includingthe primary use of leg and trunk muscles oncethese principle factors have been implemented:

• Positioning of feet and body in the skilledworkers posture with a tool swing path asdescribed in figure 31.

• Tool lift height not to exceed 20 inches forthe standard Pulaski, 23 inches for SuperPulaski, and 12 inches for the Combi tool.

• A work cycle time of 0.8 second or strokerate of 75 strikes per minute for the standardand Super Pulaskis. A work cycle time of0.7 second or stroke rate of 86 strikes perminute for the Combi tool.

• A hand separation of 16 inches for thestandard and Super Pulaskis, and 23 inchesfor the Combi tool.

• Starting grub cycle with a right shoulderangle of 6 degrees when leading with theright hand and vice versa with left hand.

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Figure 33—Pace tool strikes with a metronome.

Hand Separation—Obtain a 36-inchlength of 1-inch elastic band. This canbe easily obtained from the notionssection of a general-purpose store for acost of around $1.00. Measure off2 inches and mark; continue with 16 moreinches and mark with a “Pul”; continuewith 7 more inches and mark “Com”;measure 2 more inches and cut. Loopand tie the ends of the elastic to the wriststraps of each glove at the appropriatemark for the tools in use. The handseparation for the standard Pulaski andSuper Pulaski is 16 inches, and 23 inchesfor the Combi tool. See figure 34.

Figure 32—Tool lift height indicator with a stake and colored dowels.

Stroke Rate - Work Cycle Time—Use a tape recordingof a metronome set at 75 beats per minute or buy ametronome at a local music instrument shop. Cost for abattery powered metronome with a loud beep and a speedrange of around 75 beats per minute is $12 to $22. Thework cycle time for a complete stroke is 0.8 second, whichequals 75 beats per minute for the standard and SuperPulaskis. The work cycle time for the Combi tool is0.7 second or 86 beats per minute. Workers can speedup or slow down in pace with the metronome. See figure 33.

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Figure 34—Hand separation maintained within set parameters by elastic cord.

Right Shoulder Angle—Buy a 10-ounce plastic sack of rice. Openthe plastic sack at the end. Pour out half of the rice and fold over theend of the sack onto itself. The sack should be about 3 x 4 inches andloosely filled. Wrap securely with duct tape, keeping the sack still loosein general shape. Attach a short cord to the rice sack. Use duct tapeto secure the bag into position approximately 3 inches below the armpitof your shirt on your non-dominant side/arm, usually the left arm ofmost people. Another method is to secure the rice bag in positionwith a short cord around the rice bag and the other end attached toyour fire shirt. Position the rice bag into place 3 inches below thearmpit and against the upper torso by applying pressure with the upperarm. See figure 35. Attempt to maintain the bag against the torso,especially in the up-stroke phase. This will maintain a narrow rightshoulder angle and short arm reach.

Figure 35—Bag in position to maintain a narrow right shoulder angleand arm reach.

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Participant Ranking of ToolsAfter using all three tools, the workers were asked to rank each tool in comparison with the othertools for eight different features. Test worker ratings were averaged for the group, on a scale fromnegative 5 to positive 5. Participant rankings of the three test tools are shown in table 2.

Table 2—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 4Effectiveness 1 1 -1 3 5 1Versatility 0 0 2 4 2 3Less Fatigue—Hand and Arm -1 -3 3 -3 -4 1Less Fatigue—Lower Back 2 1 3 -3 -4 1Safety—Control 1 -1 4 4 2 1Less Shock—Handle absorption 2 1 2 2 1 4Better Grip 2 0 4 2 1 4

Key for Ranking Most Negative = -5 No Difference = 0 Most Positive = +5

The standard Pulaski was ranked high by skilledworkers for versatility and safety; low by bothgroups for quality of line and effectiveness; andfair on grip and shock absorption of handle.

The Super Pulaski was ranked high for bothgroups for quality of line and effectiveness; rankedhigh for causing fatigue in arms, and lower back;and ranked low in safety/control and versatility.

The Combi tool was ranked high by both groupsfor grip, shock absorption of handle, reducedback, and arm fatigue. The Combi tool was rankedhigh by regular workers for versatility and safety/

control, but ranked low for the same factors byskilled workers.

The Combi tool was ranked low by both groupsfor quality of line and effectiveness. However,test results in this study, as described in aprevious section, show that use of the Combitool provides a higher productivity, lower energycost, and higher safety aspects than the standardor Super Pulaski. This is indicative of a strongtool bias. This is an indicator that the benefitsof the use of the Combi tool have not been fullyrealized.

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Experience, Strength, and Fitness ScoresExperience, strength, and fitness scores are shown in table 3.

Table 3—Experience, Strength and Fitness Scores

Regular Skilled

Number of fires fought, average 168 127

Number hours digging line, average 1,816 2,200

Height average 5 ft 8 in 5 ft 9 in

Height range 5 ft 8 in - 5 ft 9 in 5 ft 4 in – 6 ft 2 in

Weight pounds 176 164

Weight range pounds 163 to 192 135 to 202

Age, years 33 30

Gender F, F, M M, F, M

Percent body fat 33 22

Number chin-ups 5 12

Chin up range of values 0 to 15 6 to 20

Right hand grip force, pounds 121 116

Left hand grip force, pounds 112 113

1-1/2 mile run 13 min 38 sec 9 min 46 sec

The best indicator for work capacity is the packtest. Pack test results were not available for alltest participants and are not included.

The time required for the 1-1/2 mile run was40 percent higher and percent body fat was50 percent higher in regular workers as comparedto skilled workers. These are significantdifferences in levels of physical fitness criticalto firefighter performance with the potential for

accidents or injury. An appropriate minimumperformance standard, based on physicalrequirements for skilled firefighters, is crucialto safety. In addition, it is important to have areserve available for use in emergencies. Specificsteps for wildland firefighters to achieve andmaintain fitness and work capacity are welldescribed in the National Wildfire CoordinatingGroup publication “Fitness and WorkCapacity” (20).

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Participant CommentsIn the survey, regular and skilled workers were asked to comment on the test tools. Their commentsare summarized in table 4.

Table 4—Summary of Comments From regular and Skilled Workers

• Standard Pulaski - I like the balanced weight as compared to the Super Pulaski. Idislike the back fatigue. Weight of tool on downswing is the key.

• Combi tool is easy to use, feels light. Handle diameter is too big, so can’t get a goodgrip.

• I like the big grub end of the Super Pulaski. I think it’s more efficient, but I don’t like theodd balance on the head.

• The Super Pulaski does not require as much effort to pound, just let it drop and pull it.

• Combi tool is OK, but the handle is about 2 inches too long.

• The standard Pulaski is all right. It’s light and might be more effective if the grubbingend was bigger. The same worker commented that the Super Pulaski is a little heavy.It might be more effective if made with a lighter metal.

• The Super Pulaski hurts my hands because of the weight.

• Super Pulaski is good to use gravity for swing.

DISCUSSIONThese results reflect a firefighter population ofaverage height and weight and may not becompletely applicable to firefighters over 6 feetor shorter than 5 feet 4 inches. Additionally, onlyone fuel type and one soil compaction wereinvestigated.

Criteria for firefighters: six workers, each with aminimum of two years fireline experience. Arandom selection of tools was used by eachworker. Since a minimum of two years experiencewas required, a learning curve was not expectedto be a factor affecting performance results andkinematic measurements.

Test conditions were controlled as follows:

• The warm-up regimen was consistent andincluded stretching and range of motion,with and without a tool. Test workers had a3-minute warm-up period of grubbing witheach test tool, for a total of approximately5 minutes of grubbing per tool.Consequently, analysis did not considerfatigue effects on performance.

• Delivery of instructions/training given wereuniform and consistent to all workers.

• The ambient temperature variations werenot significant over the test time period, soanalysis did not consider the effect oftemperature on performance.

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• Data were collected for a total of 25 strikesor more. The first strike and last 3 strikeswere omitted from analysis since theyreflected the beginning and end of grubbing.Furthermore, during testing, data cycleswere removed when workers wiped theirface, stopped for a drink, or changed hands.

• Test instrumentation was positioned to allowthe workers to grub without beingconstrained by data collection. The sensorswere mounted securely to the body part.Consequently, the sensor/body system actedas a rigid body.

• Data was not shared with test workers untilall testing was completed. This was donein order to prevent competition between testworkers and between tools for each testsubject.

• The Project Leader signaled the test crewto begin gathering data without theknowledge of the test worker.

A portable backpack version of the biomechanicalanalysis system is in commercial developmentfor ski professionals. This system could be usedas a portable backpack test unit for field testingon the fireline. The transmitter and laptop are inthe backpack. This allows testing of biomechanicson the fireline over a prolonged period to assesseffects of fatigue on physiology.

Six hours of technical videotape have beencollected during field testing. If a training videois developed in the future, it is recommendedthat this technical videotape be used for slowmotion segments.

The training program was piloted with excellentpreliminary results. However the training programrequires further refinement for use by Type IIcrews. IHC crew bosses would provide valuableinput on the development of this training programand could impart additional skills beyond proper

body positions and tool techniques involved inusing leg and trunk muscles for the skilled useof fire hand tools, especially by Type II crews.

Results verification testing needs to beconducted, followed by field testing in severalregions, and the training program refined asappropriate for Type II crews. Interagency HotshotCrew Superintendents can identify a group ofregular firefighters; and a kinematic analysis oftheir motions would be conducted before andafter training. Train to the newly definedparameters and re-test at the new skill level.Compare the motions of the trained firefightersto the motions of skilled firefighters identified inthis report. If the newly trained firefighters usemotions within one standard deviation of themotions of skilled firefighters, then the trainingprogram will be considered effective. For anymotions not within one standard deviation, thatpart of the training program should be rewrittenand results verification repeated.

Bias, tradition, and attitude must be recognizedin participant ranking, tool use, and selection.There is field bias towards and against certaintools. This was proven in testing. Somefirefighters commented on expectations ofperformance via participant rankings that werein direct contrast to actual biomechanical testvalues. In addition, it is not unusual for bias topersist despite use of the non-traditional tool,especially if tool use was mandated.

CONCLUSIONSFrom this test it can be concluded that:

The Combi tool should be the first training toolused by regular firefighters in developing skilledtechnique. The Combi tool should also be usedto train experienced firefighters to become moreefficient. In addition, the Combi tool should bedesignated as the first grubbing tool of choicein light flashy fuels in decomposed granite, andwhen fuel type and soil conditions permit. This

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has been determined by low energy cost, highproductivity, and safety aspects of the Combitool, especially for the regular firefighter, ascompared with the standard and SuperPulaskis. However, responses from firefighterinterviews at the end of each test cycleindicated:

• The standard Pulaski was rated high by bothgroups for less fatigue to the hand and arms,and high for versatility and safety.

• The Combi tool was rated poor for lessfatigue to the hand and arms, fair for qualityof line and versatility, and high by bothgroups for less shock to the handle andbetter grip.

• The Super Pulaski was rated high for qualityof line and effectiveness by both groups,but the skilled group rated it much higheroverall.

• Super Pulaski ranked high for quality of lineand effectiveness, and low on shockabsorption of handle and poor grip.

Participant rankings for the Combi tool oneffectiveness and quality of line were the lowestfor all tools, indicating a strong tool bias andlow field acceptability. It can be concluded thatthe benefits of the Combi tool have not beenfully realized. Top priority should be given to abroad field implementation of the Combi tool.This tool should be included in crew tool mixes,especially for Type II crews.

Regular workers primarily used arm and shouldermuscles, and skilled workers primarily used legand trunk muscles for grubbing with the standardand Super Pulaskis. Consequently, regularworkers using the standard and Super Pulaskisare expected to fatigue much more quickly thanskilled workers due to the size difference of thesemuscles. With the Combi tool, regular workersagain used arm and shoulder muscles, but alsoused some leg and trunk muscles. Regular

workers are expected to fatigue quicker with thestandard and Super Pulaski as compared to theCombi tool. Firefighters with a poor grip anddecreased upper body strength have a greaterpotential for injury with the use of the SuperPulaski. Consequently, the Combi tool is the safer,more efficient tool for regular firefighters todevelop their skills.

Key Biomechanical ParametersBased on kinematic motion analysis, adetermination has been made that there areseveral key biomechanical parameters that definesignificant differences in body posture, grubbingmotions, productivity, energy expended, andpotential for injury between skilled and regularfirefighters. There is a significant correlationbetween both amplitude and duration of specificbiomechanic parameters and skill level. The keypoints determined are:

Shoulder and Hand Separation MotionsWith the standard Pulaski, regular workersperform the first half of shoulder and handseparation motions similar to that of a skilledworker, but draw out the second half of themotion and perform it much more slowly.These differences are much more pronouncedand distributed among a greater number ofthe joints with the Super Pulaski. Joint angleprofiles of regular and skilled workers arethe most similar for use of the Combi toolwhen compared to the standard and SuperPulaskis.

Tool Strike RateThe standard Pulaski has a 3-inch hoe blade.Regular workers can strike/grub 55 strikesper minute, or 165 inches per minute. Skilledworkers with 75 strikes per minute can strike/grub 225 inches per minute with the standardPulaski. Skilled workers are 36 percent moreproductive as determined by tool strike ratewith the standard Pulaski.

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The Super Pulaski has a 6.8-inch hoe blade.Regular workers can strike/grub 40 strikesper minute, or 272 inches per minute. Skilledworkers can strike/grub at 75 strikes perminute, or 510 inches per minute with theSuper Pulaski. Skilled workers are 88 percentmore productive as determined by tool strikerate with the Super Pulaski. However, aprevious fire tool study conducted by SDTDChas determined that there is a substantialincrease in the energy cost to the firefighterthat far exceeds this increase in production.Also, there are safety concerns with the useof some configurations of the Super Pulaski.

The Combi tool has a 4-inch serrated blade.The regular worker with 67 strikes per minutecan strike/grub 268 inches per minute. Theskilled worker with 86 strikes per minute canstrike/grub 344 inches per minute with theCombi tool. Skilled workers are 28 percentmore productive as determined by tool strikewith the Combi tool. The Combi tool is themost efficient tool based on the low energycost, high productivity, and safety, especiallyfor the regular firefighter.

Production RatesUsing standard hand crew production ratesfor medium brush for a line width of 6 feet,skilled workers using the standard Pulaskican complete 75 tool strikes for every 55 byregular workers. Productivity can increaseby 68 feet per hour if the whole crew wastrained to the skilled level. This productivityincrease is comparable to having 2 peopleadded to a 15-person crew.

Using the Super Pulaski, skilled workerscomplete 75 tool strikes for every 40 strikesby a regular worker. Productivity can increaseby 136 feet per hour if the whole crew wastrained to the skilled level. This is comparableto having 4 people added to a 15-person crew.

Using the Combi tool, skilled workers cancomplete 86 tool strikes for every 67 strikesby a regular worker. Productivity can increaseby 55 feet per hour if the whole crew wastrained to the skilled level. This is comparableto having 2 people added to a 15-person crew.

Tool Head Impact and G ForceTool impact and G force were substantiallyhigher for a regular worker when comparedto a skilled worker. This is partially due tothe increased lift height and the increasedangular velocity resulting from the extendedreach of a regular worker. This extendedreach causes work on the back for tworeasons. First, back exertion will be requiredto support the motion. Secondly, the tool willbe buried further into the ground causing morestrain on the back to free the tool blade tocomplete the motion cycle.

The tool impact force for a regular workerusing the standard Pulaski was 4.5 gs, or aG force of 24.0 pounds, as compared to theskilled worker with an impact of 2.7 gs, or aG force of 15 pounds. This means the regularworker pounded the ground 67 percent harderthan a skilled worker with the standardPulaski.

The tool impact force for a regular workerusing the Super Pulaski was 5.3 gs, or aG force of 37 pounds as compared to theskilled worker with an impact force of 2.9 gs,or a G force of 8 pounds. This means theregular worker pounded the ground83 percent harder than a skilled worker withthe Super Pulaski.

The tool impact force for a regular workerusing the Combi tool was 3.0 gs, as comparedto the skilled worker tool impact force of1.8 gs. This means the regular workerpounded the ground 67 percent harder thanskilled with the standard Pulaski.

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Tool Head HeightAgain, as described in the previous section,an increased tool lift height is due in part toan increased arm reach, which causesincreased work on the back and inefficientuse of energy. An increased tool lift heightis an indicator of a need for training. Tool liftheight can be reduced to an optimum lift withproper training. A regular worker elevates thestandard Pulaski tool head to 32 inches,60 percent higher than a skilled worker at20 inches.

A regular worker elevates the Super Pulaskitool head to 41 inches, 78 percent higher thana skilled worker at 23 inches. A regular workerelevates the Combi tool head to 21 inches,75 percent higher than a skilled worker at12 inches.

Energy ExpenditureThe Combi tool has the lowest energyexpenditure for the same amount of workwhen compared to the standard and SuperPulaski. Consequently, the Combi tool is themost efficient tool tested.

Regular workers, with a standard Pulaski,expend the same amount of energy in twocycles that is expended by a skilled workerin three cycles simply by lifting the tool headhigher. As described in the previous section,an increased tool lift height is an indicatorof a need for training. Regular workers usingthe Super Pulaski expend the same amountof energy in one cycle that is expended byskilled workers in two cycles, simply by liftingthe tool head higher.

Regular workers with the Combi tool expendthe same amount of energy in two cycles thatis expended by skilled workers in three cycles,simply by lifting the tool head higher. Eventhough the cycles are the same between thestandard Pulaski and Combi tool, several

differences in tool design exist thatsignificantly affect energy expenditure. TheCombi tool weighs 18 percent less than thestandard Pulaski. The Combi tool is closerto being a balanced tool than the standardPulaski because most of the weight of theCombi tool is in the handle and it has alightweight tool head. Finally, the tool liftheight is 12 inches for the skilled workerversus 20 inches on the standard Pulaski.However, this difference is offset by a longer40-inch handle, versus a 34-inch handle forthe Pulaski. Consequently, the Combi toolhas the lowest energy expenditure for thesame amount of work when compared to thestandard and Super Pulaski.

Body Posture and Physical FitnessWith the Combi tool, body posture—atmaximum lift height and tool strike—did notvary to the same level of differences betweenregular and skilled workers using the standardand Super Pulaskis. This indicates that theCombi tool is the easiest tool on which touse to train regular workers to become skilledusers.

Firefighters can reduce the potential for carpaltunnel syndrome and injury by beingphysically fit for the job, using the bestgrubbing technique for each fire tool, takingfrequent rest breaks, rotating tools acrossfirefighters, and holding the tool with a morenatural hand position with good grippingaction. These techniques are especiallyimportant for Type II crews who are nottypically as work-hardened as Type I IHCcrews.

There are significant differences in the levelsof physical fitness between regular and skilledfirefighters. The time required for the 1-1/2 mile run was 40 percent higher and percentbody fat was 50 percent higher in regularworkers than skilled workers. These are

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significant differences in levels of physicalfitness that are critical to firefighterperformance and the potential for accidentsor injury. An appropriate minimumperformance standard based on physicalrequirements for skilled firefighters is crucialto safety. In addition, it is important to havea reserve available for use in emergencies.These findings indicate that minimumperformance standards need to be revisedto a higher level of physical fitness. Specificsteps for wildland firefighters to achieve andmaintain fitness and work capacity are welldescribed in the National WildfireCoordinating Group publication “Fitness andWork Capacity.”

New tool configurations need to be developedwith optimal user technique design criteriato include a balanced lightweight tool head,ergonomic handle, optimum hoe blade width,and optimum handle length. Safety andproduction are the ultimate criteria.

There is a safety concern with the use of theSuper Pulaski, as determined by analysis ofkey biomechanical parameters. Regularworkers do not have good control andguidance of the Super Pulaski. It is liftedhigher and has a greater tool head mass,contributing to increased momentum on thedown stroke. Also, the non-dominant foot isin the path of the tool head. A lost time studyrelated to fire hand tools, specifically theSuper Pulaski, has not been conducted. TheSuper Pulaski, as currently designed, shouldnot be used by regular workers.

The fire tool survey of the IHC network hada response rate of 75 percent. Suggestionsincluded tool modification information,hardware, and drawings of standard, modified,and specialty fire hand tools currently inservice. The high response rate indicates ahigh level of interest in tool design and use.

Modifications varied from crude to prototypemodels meeting some aspects of basic handtool design criteria. Some of the modifiedtools have wide field acceptance, such asthe Bosley and Rhinehart. Somemodifications of the standard Pulaski arerefined designs with a hoe blade width of4.5 inches. Some of these tool modificationswarrant further study with findings reportedto the field. These findings are to includepros and cons of commercial and field toolmodifications with associated science-baseddesign rationale.

Type I and Type II crews, using the describedtraining program, can readily acquire thenecessary skills to use fire hand tools moreeffectively and safely, including using leg andtrunk muscles to provide for a sustainablework rate. The proposed training programneeds further refinement with the assistanceof crew bosses, including hard copy andelectronic computer training modules,posters, and video. Training material shouldbe developed based on key biomechanicalparameters and pacing for a sustainableworkrate. Skilled firefighters are able to pacethemselves in order to maintain a sustainableworkrate. Skilled workers appear to use thesame amount of power, regardless of the toolweight by varying the lift height accordingto tool weight— less lift for more givenweight—and have been observed to movethe position of the hands according to theweight of the tool head, closer to the toolhead for increased weight. Resultsverification testing, with field evaluation inseveral regions, should be conducted todetermine if the training module is effective.Verification testing is achieved by conductinga biomechanical evaluation of regularfirefighters trained to the newly definedparameters and re-tested at the new skilllevel. A comparative analysis should beconducted between the before and aftertraining data.

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Identification of the optimum biomechanicsassociated with the use of the shovel andMcLeod hand tools should be conducted inorder to contribute to improvements inper fo rmance, w i th a reduc t ion inergonomically induced injuries. In addition,this biomechanical data can be used toconduct a quantitative dynamics andacceleration data comparative analysisbetween skilled and regular firefighters todetermine the amounts of stress on joints.In addition, the net dynamic moments andforces of firefighters from kinematic data,body segment mass and dimensionparameters, force plate ground reactionvectors, and kinematic and kinetic data canbe obtained and used to understand andreduce stresses on the joints.

RECOMMENDATIONSBased on the findings of this test:

Top priority should be given to the broad fieldimplementation of the Combi tool, increasingfield acceptance, and including the Combitool in crew mixes, especially for Type IIcrews. The Combi tool should be the firsttraining tool used by regular firefighters indeveloping skilled technique. The Combi toolshould also be used to train experiencedfirefighters to become more efficient. Inaddition, the Combi tool should be designatedas the first grubbing tool of choice in lightflashy fuels in decomposed granite, and whenfuel type and soil conditions permit, asdetermined by low energy cost, highproductivity, and safety aspects of the Combitool when compared with the standard andSuper Pulaskis.

The Super Pulaski, as currently designed,should not be used by regular firefighters.

Conduct a lost time 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 hand tools moreeffectively and safely, including using leg andtrunk muscles, the key biomechanicsparameters, and pacing for a sustainable workrate. This training program would teach Type Icrews to enhance efficiency. The proposedtraining program needs further refinementwith the assistance of crew bosses, to includehard copy and electronic computer trainingmodules, posters, and video.

Minimum performance standards forfirefighters should be revised to a higher levelof physical fitness and work capacity. Wildlandfirefighters should be encouraged to achieveand maintain fitness and work capacity asdescribed in the National WildfireCoordinating Group publication “Fitness andWork Capacity.”

Identification of the optimum biomechanicsassociated with the use of the shovel andMcLeod hand tools should be conducted inorder to contribute to improvements inperformance with a reduction in ergonomicallyinduced injuries.

Development of new tool configurationsshould continue to be based on rigorousscientific methodology. The developmentalfocus should continue to be based onfirefighter input, impact on cutting ability, toolbalance, kinematics, and safety, and includefield testing in a variety of fuels and soilcompactions. Tool redesign should follow theFire Tool Experimental Design Matrix andshould consider:

• Balancing of all standard fire tools shouldbe conducted, to include bringing thecenter of gravity in line with the handlecenterline. Balancing tools may includeincreasing the handle length of the Pulaski,

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and reducing diameter and handle lengthof the Combi tool. Determine the optimumblade width of the Pulaski hoe blade.

• Testing should be expanded to continueprior development study into new handleconfigurations and materials for increaseddurability and strength, incorporating newtechnology regarding ergonomicconsiderations and materials.

• Data from the SDTDC fire tool surveyshould be further analyzed and the findingspublished in a report or catalog for fielddistribution. Findings should includevarious commercially available specialtyfire hand tools and the pros and cons ofcommercial and field tool modificationslisted with associated science-baseddesign rationale.

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BIBLIOGRAPHY

References Cited1. Chapanis, A. 1985. Some reflections on progress. In: Proceedings of the 29th Annual Meeting of

the Human Factors Society, Human Factors Society. 1-8.

2. Jukkala, Art., and Sharkey, Brian J. 1988. An improved wildland firefighting hand tool. Proj. Rep.8851-2802-MTDC. Missoula, MT: U.S. Department of Agriculture, Forest Service, MissoulaTechnology and Development Center.

3. Sicking, Lois P. 1995. Fire tool ergonomics interim report, Proj. Rep. 9551-1208-SDTDC. SanDimas, CA: U.S. Department of Agriculture, Forest Service, San Dimas Technology andDevelopment Center.

4. Chung, Jeffery Y. 1995 and 1997. Personal communication. Field Support Department Head,Lawrence Berkeley National Laboratory, U.S. Department of Energy.

5. Jukkala, Art. 1997. Personal communication. Retired, USDA Forest Service, Missoula Technologyand Development Center.

6. Isernhagen, Susan J. 1988. Work injury: management and prevention. Aspen Publishers, Inc. 68-69.

7. Sicking, Lois P. 1997 and 1998. Test plan for evaluating the biomechanics of fire tools. Unpublishedproject test plans. San Dimas, CA: U.S. Department of Agriculture, Forest Service, San DimasTechnology and Development Center.

8. Putnam, Ted. 1995. Heavy duty leather gloves, resized, improved and NFPA compliant. Proj.Rep. 9567-2332-MTDC. Missoula, MT: U.S. Department of Agriculture, Forest Service, MissoulaTechnology and Development Center.

9. Preventing illness and injury in the workplace. April 1985. Washington, DC: U.S. Congress, Officeof Technology Assessment, OTA-H-256, Chapter 7, Ergonomics and Human Factors. 128-129.

10. Johnson, Barry L. 1989. Congressional testimony. Subcommittee on Postal Personnel andModernization Committee on Post Office and Civil Service. Washington, DC: U.S. House ofRepresentatives, “Carpal Tunnel Syndrome, Selected References,” National Institute forOccupational Safety and Health.

11. Frymoyer, J. 1985. The challenge of the lumbar spine. Abstracted. Minneapolis, MN.

12. Snook, S. 1983. Proceedings of the conference on industrial low back pain. University of Vermont.

13. Pizatella, Timothy J., Nelson, Roger M., Nestor, David E., and Jenson, Roger C. 1986. The NIOSHstrategy for reducing musculoskeletal injuries. Washington, DC: National Institute for OccupationalSafety and Health.

14. McMahan, Paul B., and Page, George B. 1986. An evaluation of hand tool design and method ofuse of railroad hand tools on back stress and performance. Rep. No. R-639. Chicago, IL: AARTechnical Center.

15. Ozkaya, Nihat., and Nordin, Margareta. 1991. Fundamentals of biomechanics, equilibrium, motion,and deformation. New York: Van Nostrand Reinhold. p.123.

56

16. Armstrong, Thomas J., Punnett, Laura, and Ketner, Philip. 1989. Subjective worker assessmentsof hand tools used in the automobile industry. American Industrial Hygiene Association. 50 (12):639-645.

17. Riley, M.W., Cochran, D. J., and Schanbacher, C. A. 1985. Force capability differences due togloves. Ergonomics. 28:441-447.

18. Wanj, M.J., Bishu, R.R., and Rogers, S.H. 1987. Grip strength changes when wearing three typesof gloves. In: Human Factors Interface 1987: Western New York Human Factors Society; Rochester,N.Y.

19. Sharkey, Brian. J. 1989. Fatigue & the fire fighter. NFES 2072. Missoula, MT: U.S. Department ofAgriculture, Forest Service, Missoula Technology and Development Center. 6-8.

20. Sharkey, Brian. J. 1997. Fitness and work capacity, second edition. Tech. Rep. 9751-2814-MTDC.Missoula, MT: U.S. Department of Agriculture, Forest Service, Missoula Technology andDevelopment Center. 78 p.

Additional ReferencesThe following references provided additional information. These references may be obtained from apublic or university library.

Brigden, Roy. 1997. Agricultural hand tools. Shire Publications Ltd.

Budd, Grahame; Brotherhood, John; Hendrie, Leigh; Chaney, Phil; and Dawson, Mark. 1996. Safeand productive bush firefighting with hand tools. Commonwealth of Australia.

Criteria for a recommended ergonomics standard. 1989. Pub. No. 89-106. Washington, DC: U.S.Department of Health and Human Services, National Institute for Occupational Safety and Health.

Cumulative trauma disorders in the workplace. 1995. Washington, DC: U.S. Department of Healthand Human Services, Public Health Service, Centers for Disease Control and Prevention, NationalInstitute for Occupational Safety and Health.

Darss-Mueller, H. 1982. The significance of ergonomics to agroforesty. Institute of Ergonomics of theFederal Research Center for Forestry and Forest Products. Hamberg-Reinbek.

Grood, E.S., Suntay, W.J. 1983. A joint coordinate system for the clinical description of three dimensionalmotions: application to the knee. Journal of Biomechanical Engineering, Vol. 105.136-144.Joint Army-Navy-Air Force Steering Committee. 1972. Human engineering guide to equipment design,revised edition. John Wiley & Sons.

Hallman, Richard G. 1988. Hand tools for trail work. Pub. No. 8823-2601-MTDC. Missoula, MT: U.S.Department of Agriculture, Forest Service. Missoula Technology and Development Center.

Johnson, I.M., and O’Neill, D.H. The role of ergonomics in tropical agriculture in developing countries.National Institute of Agriculture Engineering.

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King, Barry G., and Showers, Mary Jane. 1987. Human anatomy and physiology, fifth edition.W.B.Saunders Company. 171 and 189.

Kroemer, K.H.E., Kroemer, H.J., and Kroemer-Elbert, K.E. 1990. Engineering physiology bases ofhuman factors/ergonomics, second edition. Van Nostrand Reinhold.

Lagerlof, Elisabeth. 1979. Accidents–their causes and prevention. National Board of OccupationalSafety and Health, Stockholm, Sweden.

Logan, S.F., Groszewski, P., Kreig, J.C., and Vannier, M. 1988. Upper extremity kinematics assessmentusing four coupled six degree of freedom sensors. Instrument Society of America. Paper number 88-0211, 0067-8856/88/075-081. St. Louis, MO: Washington University School of Medicine.

MacLeod, Dan. 1995. The ergonomics edge. Van Nostrand Reinhold.

Pearson, Jon, Hayford, John, and Royer, Wedi. 1995. Comprehensive wellness for firefighters. VanNostrand Reinhold.

Raab, Frederick H., Blood, Ernest B, Steiner, Terry, and Jones, Herbert R. 1979. Magnetic positionand orientation tracking system. IEEE Transactions on Aerospace and Electronic Systems, Vol. AES-15, Number 5.

Radwin, Robert G., and Haney, Jonathan T. 1996. An ergonomics guide to hand tools. AmericanIndustrial Hygiene Association. Fairfax, VA.

Rodgers, Suzanne H. 1983. Ergonomic design for people at work. Volume 1, Van Nostrand Reinhold.

Rodgers, Suzanne H. Matching worker and work site-ergonomics principles.

Saunders, Mark S., and McCormick, Ernest J. 1993. Human factors in engineering and design, seventhedition. New York: McGraw Hill, Inc. 399 p.

Selan, Joseph. 1994. The advanced ergonomics manual. Advanced Ergonomics, Inc.

Sharkey, Brian J. 1989. A study of wildland firefighting work/rest cycles. Proj. Rep. 89-35-MTDC.Missoula, MT: U.S. Department of Agriculture, Forest Service, Missoula Technology and DevelopmentCenter.

Sharkey, Brian J. 1980. Development and evaluation, muscular fitness tests. Proj. Rep. 8051-2201-MTDC. Missoula, MT: U.S. Department of Agriculture, Forest Service, Missoula Technology andDevelopment Center.

Sharkey, Brian J. 1985. Fit to work. NFES 1595. Missoula, MT: U.S. Department of Agriculture, ForestService, Missoula Technology and Development Center.

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Sharkey, Brian J.1984. Physiology of fitness. Champaign, IL: Human Kinetics Publishers, Inc.

Sirosis, Al. 1967. Evaluation of fiberglass handles. Proj. Rep. 1404.1. San Dimas, CA: U.S. Departmentof Agriculture, Forest Service, San Dimas Technology and Development Center.

United States Department of Health and Human Services. 1981. Work practices guide for manuallifting. National Institute for Occupational Safety and Health, Cincinnati, OH.

Van Loon, J.H, Staudt, F.J., and Zander, J. 1979. Ergonomics in tropical agriculture and forestry.Center for Agricultural Publishing and Documentation, Wageningen, The Netherlands.

Webb, R.D.G., and Hope, P.A. 1983. Ergonomics and skidder operations in northern Ontario. InformationReport DPC-X-15, Canadian Forestry Service.

Woodson, Wesley E., Tilllman, Barry, and Tillman, Peggy. 1992. Human factors design handbook,second edition. McGraw-Hill, Inc.

Woodson, Wesley E., and Conover, Donald. 1970. Human engineering guide for equipment designers,second edition. University of California Press.

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APPENDIX A

DefinitionsAdduction – Abduction. Adduction is movementtoward the body, such as in right shoulderadduction. It occurs in the shoulder joint when araised arm is lowered. Abduction is movementaway from the body, such as in right shoulderabduction. It occurs in the shoulder joint whenthe arm is lowered and raised, respectively.Adduction is the opposite of abduction.

Flexion – Extension. Flexion is bending,decreasing the angle between different parts ofthe body. Flexion is performed at the elbow jointwhen the forearm is bent back on the arm.Extension is straightening the arm, increasingthe angle between different parts of the body.Flexion is opposite extension.

Internal - External Rotation. Rotation is turninga body part on an axis without displacement.

Joint Angle Profile. Graph that shows how theangular position of a joint varies over the durationof the motion. Measurement of this allows acomparative analysis between different workerscompleting the same motion. This is importantbecause a determination can be made of theoptimum motions, presenting the opportunity tochange a regular motion to a different skilledmotion. Standard deviation of biomechanicalvalues is also indicated.

Joint Angular Velocity Profile. Graph that showshow the angular speed of a joint varies over theduration of the motion. These are similar to thejoint angle profile but indicate the speed ofmovement.

Motion Cycle Time. The time for a singlecomplete cycle of the motion to occur, also calledtool stroke rate. For example the grubbing motionstarts as the firefighter begins lifting the tool headfrom the soil and ends the next time the head

impacts the soil. Comparing the cycle times ofskilled and regular workers indicates how quicklya specific length of fireline can be constructed.However, the effectiveness of grubbing techniqueis not addressed by the motion time cycle.

Peak Angular Velocity. The fastest or greatestmeasured value of the “Joint Angular VelocityProfile”.

Posture at Maximum Tool Lift Height andPosture at Tool Impact. The positions of thebody at the time of maximum elevation of thetool head from the ground, and when the toolhead impacts the soil. These two positions appearto indicate significant differences in the overallmotion. For example, in general the posture atmaximum tool height for regular workers has thetool and arm segments much higher than thoseof the skilled worker. This indicates a greaterwork input to elevate both the tool and the arms.The posture at tool impact for regular workersis generally more out stretched than skilledworkers. The out stretched posture results ingreater load translated to the lower back,predisposing the worker to lower back strain.

Pronation – Supination. Pronation is turningthe palm and forearm downward. Supination isthe turning the palm and forearm upward.

Range of Motion. The angular range from thesmallest bend angle to the greatest bend angle.For example, the knee has a range of motion fromapproximately 0 degrees with the knee locked, to160 degrees with the heel nearly touching the backof the thigh. Comparing this between a regular andskilled worker provides information regarding thedistance the worker traveled through the full rangeof motion. In the case of the range of motion forthe upper extremities, some of these ranges indicategreater effort or work output.

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Standard Deviation. A statistical measure of thevariation of a parameter about the average for agroup. This measure can be used to evaluatesimilarity between groups and variation betweenindividuals of the same group. To make evaluationsbased on standard deviation between two groups,plots are made. Plotting average graphs for twogroups with the +/-1 standard deviation bands onthe same axes, allows a visual evaluation of thesimilarity between the two groups. If the two bandshave a large overlap, the groups are similar withrespect to the parameter graphed. Conversely, ifthe two bands show little or no overlap, the groupsare dissimilar. The larger the band separationbetween two groups, the greater the differencebetween the groups. Regarding the variation of ameasured value within the group, the magnitudeor width of the band is examined. The wider theband, the greater variation within the group, whilea smaller band indicates less variation within thegroup.

Tool Impact Acceleration. Defined as the rate ofchange of velocity of the tool and is an indirectmeasure of how hard the tool head hits the ground.It is dependent on tool weight and the height thetool is lifted. Firefighters grub line to bare mineralsoil. This requires depth and area to clear allcombustible material. Consequently, the tool blademay not need to go deeper than two inches.However, the harder the tool impacts the ground,the further the blade will penetrate into the soil.Thus, the regular worker may bury the tool further

into the ground than is necessary, burying the blade,using energy to unbury the blade, then resumeproductive work. This may seem trivial at first, afterall, the worker has still cleared the area to baresoil. However, more soil than necessary has beenremoved, the blade had to be unburied; as a result,unproductive work has been done in the process.

Tool Lift Height. Tool lift height is how high upthe worker raises the tool at the beginning of thestroke. It is the vertical distance from ground tothe tool head. The higher the tool is lifted, the greaterthe amount of work done against gravity.Consequently, if a regular worker lifts the tool higherthan a skilled worker, more work has been done,i.e., expended more energy. Assuming that skilledand regular workers have the same amount ofenergy to expend, the skilled worker could performmore grubbing cycles and thus produce a longerfireline, simply because energy was not wastedby lifting the tool too far above the ground, possiblyburying the blade on impact and having to useadditional energy to unbury the blade. If the toollift height is too low, the tool may bounce off andnot penetrate the surface.

Tool Head Path. The tool head path curve indicatesthe amount of work used for each tool stroke cycleand gives an indication as to whether the bladewas buried on impact.

Ulnar/radial Deviation. The variation in positionof the ulnar and radial musculo-skeletal segment.

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APPENDIX BFire Hand Tool Test Matrix

Dependent VariablesPerformance Muscular Fatigue Ergonomics

Production of Line Posture—Back/Arm/Shoulder Pain/DiscomfortHeart Rate, O2 Debt EMG - Fatigue Strain

Independent VariablesAccident RatesAgeSex/GenderEthnicityAnthropometric Data

HeightWeightArm Length/ReachArm Circumference

Physiological DataBody Mass Index/Body FatHand/Grip StrengthArm StrengthLung Capacity/Tidal Volume Heart RateEnduranceSmokingHealthAccident History/Disability

Field ExperienceTool TrainingRest Period Intervals/DurationEnvironmental Factors

TemperatureHumidityWind Velocity/ChillTerrainVegetationSoil Type/Soil Compaction

ClothingGlovesPersonal Protection Equipment AttireFootwearGear/Pack Weight

Psychological FactorsMotivationFearCompetitivenessAttitudeTeam EffortIndividual Effort

Tool Design; Tool WeightTool Handle LengthHoe/Blade Width; Hoe/Blade Sharpness; Hoe/Blade AngleTool Aesthetics/Appearance

Test Duration (Time); Other(s); Note - Need to select and run correlation, inferential statisticalanalysis such as T-test, Chi-square, or Nonparametric tests, etc.

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APPENDIX C

Biomechanics of Fire Hand Tools Test Matrix

Subject Data: Constants

Initials ____________ Pack Test ______ gloves ___________ soil conditions ______

Age ______________ Body Fat_______ terrain ___________ grubbing rate _______

Gender ___________ Grip Force _____ fatigue effects ____ work & rest cycle ___

# of fires fought ____ Arm Pull _______ ambient temp_____ relative humidity ____

Height ____________ Arm Lift ________ wind speed ______

Weight ___________

Hours of Training in _________________ Time for 1.5 mile run __________________

Fire Hand Tool Use:

Independent Variables Dependent VariablesTool Human Kinematic Physiological Tool Kinematic

Number Values Data Points Data Points

1. Pulaski standard head Human joint linear & angular Heart rate at Tool deceleration34.5’’ wood no grip position-velocity, acceleration, 140 to 150 beats rate variations

2. Pulaski Super head deceleration (amplitude & per minute. (amplitude&34.5’’ wood no grip duration), forward bend angle, duration).

3. Combi standard head shoulder and grip position;40" wood, no grip position of feet relative to fireline.

Sensors placed @ right wrist/elbow/ shoulder T3; @ left wrist/elbow/shoulder.

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APPENDIX D

Preference Rating of Hand Tools

For each category, rank the tools you have used today.Rate on a scale of -5 to 0 to +5

With +5 being the most, -5 being the least and 0 being no difference.

Standard Super CombiPulaski Pulaski Tool

For an equal period of use, this tool produces:More line than the other tools.

As compared to the other tools, this tool is:A more effective tool

As compared to the other tools, this tool is:A more versatile tool

As compared to the other tools, this tool produces:More hand and arm fatigue

As compared to the other tools, this tool produces:More lower back fatigue

From an overall safety standpoint, this tool is:Easier to control and safer to use

As compared to the other tools, this tool produces:More vibration absorption

As compared to the other tools, this tool has:More handle grip

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APPENDIX E

Biomechanical Angle Profiles and Angular Velocity Profiles

This Appendix contains graphs and tables of biomechanical data evaluated, but not directly referencedin the data analysis section of this document.

The comparative analysis included obvious differences between skilled and regular firefighters, betweenthe standard Pulaski, Super Pulaski and Combi Tool in:

✓ work cycle time (tool stroke rate)

✓ tool lift height

✓ tool impact acceleration

✓ tool head path

✓ hand separation

✓ posture at maximum tool lift height

✓ posture at tool strike/impact acceleration

✓ range of motion, for all joints

✓ peak angular velocities, for all joints

✓ joint angle profiles, for left and right shoulder for internal/external rotation, adduction/abduction and flexion/extension

✓ joint angle profiles, for left and right elbow for pronation/supination, adduction/abduction, and flexion/extension

✓ joint angle profiles, for left and right wrist for internal/externalrotation, ulnar/radial deviation, and flexion/extension

✓ joint angular velocity profiles, for left and right shoulderfor internal/external rotation, adduction/abduction andflexion/extension

✓ joint angular velocity profiles, for left and right elbow forpronation/supination, adduction/abduction, and flexion/extension

✓ joint angular velocity profiles, for left and right wrist forinternal/external rotation, ulnar/radial deviation, and flexion/extension

These graphs and the data used to generate the graphs are not included here, but are available fromthe author upon request.

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APPENDIX F

Table of Values

Table F1—Peak Angular Velocity and Time for all Biomechanical Parameters for the Standard Pulaski,Super Pulaski, and Combi Tool.

Table F2—Body Posture at Maximum Tool Height for all Biomechanical Parameters for the StandardPulaski, Super Pulaski, and Combi Tool.

Table F3—Body Posture at Tool Strike for all Biomechanical Parameters for the Standard Pulaski,Super Pulaski, and Combi Tool.

Table F4—Range of Motion for all Biomechanical Parameters for the Standard Pulaski, Super Pulaski,and Combi Tool.

These tables are not included, but are available from the author upon request.