Comment on the Rulemaking for Safety Standard for Bicycle Helmets

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Jan. 20. 1998 BELL SPORTS R & D No. 0078 P. Z/5BELL Bm--.-_. - --___-- .- --- . -____ _ _. .---m19/l 198U. S. Consumer Product Scsfety CornmissIonc/o Scott HehProject ManagerDirectorate for Engineering SciencesWashtngton, D. C, 20207Dear sirs and Modoms,We CII~ very happy that the “Safety Standard for Bicycle HeIrnets” Isand difficultready to be fincllized and approved, ,If has been a Ionprocess. Scot Heh and his staff should be congrutulate3 for the effortthey applled dong the wa;y, We also thank the commission for provldInga process that Involved industry and consumer advocate groups.Moreaver, the ASTM bicycke helmet task group, which I chair, has beenallowed to be fnfuentlal in thfs procs The ASTTVI group is comprfsed ofIndustry, Independent test iab people, medical people, consumeradvocates, 01 Iawyer and, of course, Scott Heh. We hope that this newstandard Is implemented as qutckly as poss!bie.However, there Is one chunge In this last dtcrft standard that we stronglyoppose: The change of test head&m mass to 5 kg for Infants/t&d&s. 1hove been a strong advocate of Iower headfotm mass fof yeurs andfeei #hat I have mole infomnatlon than fs lndlctied in tab D of the briefingpackage. Moreover, the ASTM standard for Infants and toddters that Idrafted would have been In effect at least one year ago If not forodministrotlve over sight at ASTM. It b now approv# and going forwardwithamassof 3.2kgfortheAstzeheadfomrand4.0kgfortheEstreheudform, We have ...

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• Publié par: Sioc
• Nombre de lectures: 36
• Langue: English

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Jan. 20. 1998

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U. ConsumerProduct Scott Project Manager Directorate for D. 20207

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Dear andModoms, We veryha thatthe “Safety Standard forIs ready to beand approved,been and difficult process. Scot Heh andstaff should be for the effort they theWe thankthe commission for a process that Involved industrand consumer advocate groups. the ASTMtask whichI hasbeen allowed to bein Therou of Industry, Independent testpeople, medicalconsumer advocates, and,of ScottHeh. Wethat new standard Is implemented as However, thereone Inlast standardwe stronl oppose: Theof massto 5 kg for hove strongadvocate ofmass and #hat I havethan inof package. Moreover, thestandard for Infants andthat I drafted would haveIn effect atone earago notfor over ASTM.now andoin forward We nohelmets designed to weights under thestandard because of We do have otherThe Deartment of DOT, safetfor 218,used 3.5 kg for thefor andfor manyears Every stud ofthe effectiveness of thisc tt. no’ causesthe smallbeen that helmets oretoo Inmotorcycle helmets the 2.43.0feet density helmets, infant,typically ! and up

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Another source of fieldis our experience with damaged helmets returned to customer We ioneered infant/toddler bicycle helmets beginningthe earlyWe developed the Belt Shell in the absence of bicycle helmet standards, We followed our intuition, experience and test data. We pushed ourselves up to density just to make the helmets sturdier and more dent resistant in handling. We didn’t think that was too high,then we have sold hundreds of thousands of At times standards and helmets design details have forced us asas Wenow run atfor ail infant model helmets. In ail this time, with all these models, we have never seen on infant toddler helmet that was anywhere near bottoming out. Moreover,collected damaged infant/toddler helmets for several months in 1995. Not only  Inot see bottomed out helmets, I didn’t see any helmet showing poses theon thesigns of crushin question of whether the helmets arethan infant heads or do infants just not that hard,is that most of the time infants don’t all that hard. But thealso indicates that bottoming outnot a for infant helmets.

i want to offer some common sense and basic physics. first, energy Now management is often discussed regarding helmet standards.is a false concept. No helmet standard in the world even measures energy management of absorption nor have afor energy management. A helmet can absorb zero energy andpass any helmet standard in theEnergy absorption k a function of input to velocity minus rebound velocity. No standard requires a laboratory even measure rebound velocity never mind dictatingthe coefficient of restitution be less than 0.5 or something, A helmet can rebound with theinput andpass quiteMoreover, it can be imagined that absorb energyany number of liner materials better than contemporaryliners but in fact produce a very helmet, Aof good energy managers ore soft lead sheet and  impactingeither of theseroduces negligible rebound velocity. In other words, they absorbail of the impact energy. None of us are advocating these materials for helmet liners because energy absorption is notimportant for helmets. i think that an discussion of helmet test criteria that Includes the word suspect andbe misleading.

Acceleration management is what helmets are about.helmet standards accelerationand enforce acriteria that includes a maximum acceleration rate. Some standards measure other aspects of the acceleration/time event.event is caused by anbetween aand an anti!. The higher thevelocit moredistance, ofliner, required to control thecurve toset of parameters. The of a testno effect uponthickness.

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The mass of thedoes determine theusually the density, of the helmet liner in accordance withIn the case of the small Athe asthe medium adult the helmet liner will need to be 30% stiffer In the infanthelmet simply because the contact area of theonly 77% of the area Thus wlthelse equal this makes anof the medium Infant linerthan anhelmet liner. The newbornbaby about7 andcannot have on lb. Itobvious that small baby heads weigh less than their heads will asadults. So let’s suppose that AInfant heads weigh the 3.2 kg that I recommend. Now let’s Impacthead moss with the helmet designed for the 5 kg Awhich already30% stiffer than an adult helmet. Substituting 3.2 for 5 inwith allequal,  theobserved acceleration with the real Infant Is 56% higher than in the case with the heavy5 The 5 kgproduces g’sa test would produce nearly 400 g’s In an identical Impact In the given the weight of real baby’s heads. Substitutingliner resistance in 12.3  5.0l g 9.80665 12.3 =3.2 l 391 l 9.80665 l the helmetaround a 3.2will produce lower ratesfor accidents,Any argumentin favor of 5 kg headforms be even more20 kgfor or If real infants have 3 kg beads but we should test with 5 kg  wetest adult helmets for 5 kg aduit heads with 8 kg  fact,a kgfor testing wouldhelmet designers to develop helmets that could ‘absorb far more energy before bottoming out.’

123 3.2 kg l 3906 g This gross overignores the fact that the wouid not crush theto a rate. But Itfar into the that obvious that such unsuitable acceleration mtesa helmet for realActual tests that we have done andmodels we and others haveshow areasonable change over the smallreasonable thatwe tested. I propose that test headforms should be as closeto the average weight of real that we can properly controlhuman so

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and estimaterates in the realand not just in the laboratory. We thank you for your consideration of this mutter. Sincerely,

Seni orEngi neer

 Paragraph1203.5, Construction Requirementsprojections. The last sentence mentlons “fixture,’ an undefined term.this in the final draft.

‘The test geometry is as Wows: Size J M circumference __ 60 . . area 0.9 1.11 1  ..  eo ._ volume 0.85 1.17 1.29, 1          __    .

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