Download - Cows Tails Safety v3
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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
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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.
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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
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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
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