AreYourCowsTailsSafe?(ReproducedfromtextofarticlepublishedinSpeleology,Issue12,April2008)

Ithasbeensaidthatthemostabusedpartofcaversgearisthecowstail.Theygetdraggedaround,troddenon,loadedoverroughlimestone,shockloadedandwithallthis,caversstillignorethebasicfactswithsomeonlydiscardingthemwhenthesheathiswornandtheycanseetheinnercore.Whilstonedoesnotwantthistohappenbecausetheyareworn,therealwaysseemstobeanumberofcaverswhoadmitduringdiscussionseachyeararoundBCAsropetestrigatHiddenEarth,Ohwell,mineismanyyearsoldanditseemsOK.AquickglanceattheBritishCaveRescueCouncilsannualstatisticssince1995(BCRC)indicatethatnoonehashadtoberescuedfollowinganinjurycausedbyafailureoftheircowstails.(Weexcludedeventscausedbythelackofuseofacowstailandthosestatedastakingplaceduringabseiling.Oneincidentwasreportedinwhichtheinjuredpersonwasfoundattachedbytheircowstailattheheadofthepitch,seeBCRCincident24in1998.)Buthowmanypeoplehavesufferedlesserinjuriesandgotoutundertheirownsteam?ThisarticleispromptedbytherecentpublicationofareportonsomeworkundertakeninpartonbehalfoftheFrenchFederationofSpeleologyintotheperformanceofcowstails(200

6).

hockLoading&ImpactForce

hefocusofconcernaroundacowstailisthepotentialforthecavertoit

s

ra

but

Nlueof

rd

typicalSRTsetupwhenusingacowstail,willincludeinorderofconnection,somerock,ananchor

ctl

ssibleto

STreceiveaninjuryfollowingafallontotheircowstail.Astheadagehasit,isnotthefallwhichkillsyou,itisthesuddendecelerationattheend.Crawford(2003)reviewedtheliteraturerelatingtothenatureofinjurieresultingfromshockloading,whicharosemostlyfromstudiesonuseof

aircraftejectorseatandparachutes.Ofnoteinthereviewwasthefactthattheharnesscandeliveshockloadingintothebodywhichdoesnotbreakanybonesorcausespinedamage,butcanresultinsevereimpacttraumatointernalorgans(brain,heart,liver,spleen,etc.)resultingindeath(Crawford2003).Althoughthetopiciscomplex(dependingnotjustonthedecelerationforce,alsoupontherateofchangeofthedecelerationforceaswellasthetypeofharnessandtheweightoftheperson),workhasledCEN(EuropeanCommitteeforStandardisation)toadoptalimitof6ksoastominimisetheriskofinjuryfromsuddendeceleration(Crawford2003).IntheUSAava8kNhasbeenadopted(Crawford2003).Thereviewfoundevidencewhichsuggestedthatphysicallyfitpersonscouldwithstandupto12kNinparachutetypeharnesseswithoutbeinginjured(Crawfo2003).A(usuallysteel),acrab,thecowstail,amaillon,andaharnesswithinwhichthebodysits.Clearlytherockandsteelcomponentswillhardlyabsorbanyenergyoftheshockloadingfromafallingmass.Harnessesaremadefromtapeandtapeisapoorshockabsorberwhencomparedtorope(FFS2006).Curiously,theEuropeanstandardfordynamicrope(BSI1997)onlyrequiresthattheimpaforcefromdroppingan80kgmassthroughapproximately4.8mona2.8mlengthofsingleropeshalnotexceed12kN.IncontrasttheEuropeanstandardforsemistatic(i.e.lowstretchkernmantle)rope(BSI1998)onlyrequiresthattheimpactforcefromdroppinga100kgmassthroughapproximately0.3mona2mlengthofsingleropeshallnotexceed6kN.Whilstitisnotpocomputeanequivalentimpactforceforastandardweightanddrop,itisclearfromthefiguresthat

asemistaticropeisfarlessabsorbentofashockthanadynamicrope.ThisisborneoutbytestsundertakenbyFrenchFederationofSpeleology(2006)whichshowshigherpeakforceloadsduetosemistaticropesthandynamicropes.

ropTesting

yonEquipmentLtdcarriedoutalargeamountofworkfortheUKsHealthandSafetyExecutiveinto

hek

all

heworkundertakenbytheFrenchFederationofSpeleology(2006)expandsthisknowledgebase

forthe

CalculatingtheFallFactor

Thereportnotesthatthereareanumberoffactorswhichneedtobetakenintoaccountinco e

g

e80kg

isworthnotingthatasimplemodelofalengthofropewhoseendshavebeenmadeintoloopsformedbyknotssuggeststhatover20%oftheenergyistakenbytheknotsfora0.30mlongcows

DLitemsofpersonalprotectiveequipmentusedinindustrialropedaccess(Lyon2001).Partofthisworkfocusedoncowstails,orastheyareknownintheropeaccessbusiness,attachmentlanyards.Theirwork,whichuseda100kgmassfallingthroughfallfactor2,wasconstrainedbythelimitofthemeasuringequipmentbeingonly10kNforce.Someofthetestsdidresultinreadingsgoingofftscale.Evenso,itwasclearthatusingloopsindynamicropemadebysewingresultedinalargerpeaforcethanusingloopsmadebyknotsinasemistaticropewhichinturnresultedinalargerpeakforcethanusingloopsmadebyknotsinadynamicrope(Lyon2001).ThereportnotedthatWiththeknotstested,extremetighteningoccursduringtheimpact:thiswouldbeobviousoninspectionandintheworkplacethecowstailshouldbereplacedimmediately(Lyon2001).Tbyasubstantialamount.Some294dynamicfalltestswereconductedtogetherwith28strengthtestsonarangeofcowstailsincludingbothmanufactured(loopsmadebystitchingropeortape)andknotted(dynamicandsemistaticropeofvariousdiameters).Thedynamictestsusedan80kgmasstorepresentthecaver,whichisprobablyanunderestimateofacaversweight.RecentworkundertakenfortheHealthandSafetyExecutive(LUABS2005)indicatesthatitislikely(95%confidence)thattheinterval112.3kgto118.4kgcoversthetruevalueofthe95thpercentileweightofworkerswithoutequipment.TheFrenchpretensionedtheirknotsto3kNwhereasLyonEquipmentused2kN.(Forcomparison,astrongpersonmaybeabletopretensionaknottoabout0.5kNbysimplypullingonit.1)Thevalueof3kNwasbasedonpreviousworkdonebytheFrenchFederationofSpeleology(2006).Interestingly,LyonEquipmentmeasuredforcesgeneratedbyapersonabseilingandprusiking(2001)whichwerealllessthan1.6kN.

mputingthefallfactorofacowstailinuse.Theypointoutthatthelengthofthecrabplusthmaillon(typically0.18m)issignificantincomparisontothelengthofacowstail(typically0.36mand0.60m).Mostoftheirfallfactorswerequotedasbeingeither1or2butthereportdetailswhatthismeans.Clearly,whenonehasanoverallfalldistanceof0.63mfora0.36mlengthofrope(whichincludesthetwoknots),therestbeingmadeupoftwokarabinerlengths(oneswitchingfrombeinbelowtobeingabovetheconnectionpointontheharness),thenthefractionoftheoveralllengthwhichisabletoabsorbenergyisnowherenear100%asisconventionallyassumed.(Slightlyconfusingly,severaltestswereundertakenusingthedistanceofthesetupmeasuredunderthloadcalledrealfallfactors.Thisatleastreflectstheapproachusedinthestandardstomeasureropelengthswhenundertakingdroptests.)It

1 Basedon100lbforceinamodernbow,seehttp://en.wikipedia.org/wiki/English_longbowasat16October2012.

tail,reducingtolessthan5%fora2mlongcowstail(Mehew2005).Thisinfluenceoftheknotswobservedinthepeakforcesexperiencedbysamplesofthesameropebuthavingdifferinglengths(FFS2006)andalsodifferingdiameters.Thusthestateoftheknotabsorbing.RepeatedFa

as

lls

desanumberofrepeatedfallsoncowstailswhicnthesecondandthirdfall(FFS2006).Henceknotswhichhaveb

llfactor1drop(Tesport)butthiswasusing8mmrope.Inanumberoffallfactor2d

owstailsincludingone

fknotsateachend,seetableopposite.Forcomparison

ger

.

Thereportincluouseorfromafall,willabsorblessenergyinasubsequentfall,thusandhenceincreasingthepossibilityofinjury.Therewasonlyonepartialfailureonathirdfaresecondfall(FFS2006)butthesewerein9mmorsmallerdiameterofusingatleast10mmdynamicropeforonescowstails!ChoosingtheRightKnotsforIncreasedSafety

ThereportcoversawidecfromsewndynamicropcombinationsofknotsaTheworkshowedavariotheLyonEquipmentworkindicatedsomewhatlarpeakforcevalues Itshouldbebornein

Figure1hilsttheFrenchusedan80kgmass,onused100kg.However,thespreadofthedataforboththe

proper

rateachend,seeFigure2.

bingr

nergyabsorption,butitwillalsoholdthekarabinercaptive

mindthatwhilsttheFrenchpreloadedtheknotsto3kN,Lyononlyused2kNandthatwLyFrenchandLyonworkwhichmakesuptheseaveragesdoesnotstatisticallyjustifyaclaimthatanyonecombinationisbetterthananyothercombination(Mehew2008).Interestingly,testsdonewithbadlypositionedbarrelknots(FFS2006)whichmightinterferewiththegateofthecrab,seeFigure1,showedtheknotwouldmovebacktothepositionundertheshockload.Traditionalcowstailscompriseofacentralknot,normallyanoverhandloopknotwitheitherafigureofeightknotorabarrelknottoholdthekarabineAstheropeusedintheconstructionofmostcowstailsisdynamicrope,itmakessensethataknotcapableofabsorenergyisalsoused.Thebarrelknotisnotonlyagoodknotfoescanplayacriticalroleinshock

hshowedanincreaseinpeakforceeentightenedupeitherbyprior

t238,seephotoonpage6ofrops,thecowstailsfailedonthe

nse

sandmadefromtape,severalmade

cttocombinations

resultinginahigherpeakforce

rope.Thisjustreaffirmsthese

rangeofsinglelanyard

eandmanymadefromvariousndropetypes.

ationwithrespe

Figure2

oncedressed(semitensioned).Theuseofasingleknottothecentralmaillondoesgiverisetoaslightreductioninultimatesafetyasasingleknotisbeingusedforattachingtwocowstailstoacentralstrongpoint.Fortheultimateinsafetyeachsafetylinkshohaveitownattachmentknot.Byconstructingonescowstailsslightlydifferently,featurescanbeaddedthatenablethemtobeusedmoreefficientlyandincreasetheirsafetymargin

uld

.InFigure3erearetwooverhandloopknotsattachingthecows

be

stail,

afteryourcowstails?Firstifyoudofallontoyourcowstails,thenattheextpracticableopportunity(thatiswhenyouhavegottoasafelocationawayfromthepitch)you

s

toverhandknotsarelikelytobestatisticallyweakerthan

thtailstothecentralmaillon.Thisincreasesthesafetymarginaseachcowstailisindependentlyattachedtotheharness.Thesetwoknotsleaveasmallloop(whichcanlengthenedduringconstructionifnecessary)betweenthem.Thisnoweffectivelygivestheuseralongcowashortcowstailandaveryshortcowstail.Thisveryshortcowstailhasnumerousadvantages.Itcanbeusedtoattachtoanchorswheretheuserwantstobeheldincloseproximitywhichcertainlymakespassingrebelayseasier.Intheeventofrescueitgivesaveryshortattachmentpointsothecasualtyiskeptclosetotherescuer.IfteachingSRTitgivesanadditionalattachment

pointwhilepositioningthelongorshortcowstails.CaringforCowsTails

Figure3

Sohowshouldyoulooknshouldrelaxtheknotsandredressthem.Thisactionwillreducethetensionwithintheknotsandthusenablethemtoabsorbmoreoftheforcewhichwouldariseifyoufellagainontothem,thusreducingtheriskofinjurytoyou.Aftereachtripuntiealltheknots,rinsetheropethoroughlyincleanwaterandhanginadry,wellventilatedplacetodry(notinthesun).Beforeretyingtheknoti eorwear.Oncetheknotshavebeenretied,dressthemtoe heyshowanysignsofdamage,replacethem.Thechoiceisy soryourownlife!BLDNSfBesSykese

012

worksuggeststhagureofeightorbarrelknots.

nspecttheropeforanysignsofdamagnsurecorrecttyinganduniformity.Iftours,extendthelifeofyourcowstail

obMehew

amianWear

oteaddedin2

ubsequentresearchi

obMehewrope@british-caving.org.uk

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BritishCavew andclickonIncidentReports,asat16October2012.

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nHauteur&coleFranaisedeSplologie(2006)eriesoftestsoncowstailsusedformovingalongsemistaticropes.TranslatedbyDWeare.See

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