"Café de Colombia" <
[email protected]> wrote in message
news:[email protected]...
>
> When the helmet breaks, it clearly does absorb a significant amount
of
> energy that would have otherwise been transfered to the head. Your statement that "When the helmet
> breaks it essentially absorbs NO
energy"
> is absolutely untrue from a physics standpoint (so where did the
energy
> come from to break the helmet if not the fall itself, Tom?).
Then please be the first to show us the numbers. You'll find that a breaking helmet absorbs only
about 1/100th of the energy that the collapsing foam does. If you think that is significant then
perhaps you are one of those people with the 8 lb head.
> Such a safety design features are employed in the auto industry in
their
> vehicles as the well-known 'crumble-zone' technology.
I'm afraid that a head doesn't crupple well. Perhaps you can explain to us why brain injuries start
at 180 gees and a helmet is expected to crush at 300 gees? In fact, 300 gees is the highest force a
head can absorb short of death but only in the fittest men. Women and children are SOL.
> Consequently, current DOT certified helmets are actually DESIGNED
and
> INTENDED to break in an impact precisely for this very reason.
Then you will have to show a citation for that because the current DOT standard only talks about
CRUSHING of foam and nothing whatsoever about BREAKING of the helmet. Just to be helpful you can
find the federal helmet standard at
http://www.bhsi.org/cpscfinl.htm
>Your argument that the styrofoam needs to be 'crushed' (i.e. compressed)
would
> not apply to a high speed impact, but would apply to a very
low-speed
> impact. Cycling accidents are exclusively high speed impacts and
thus
> result in breakage instead of compression (they are the same species
of
> animal).
Man, I hope you aren't trying to be an engineer anywhere. Exactly what are your credentials for
making such a bizzare statement?
> Your other argument that a helmet is designed to dissipate the
impact
> forces over a larger area of the head's surface area is correct and
is a
> secondary safety mechanism of bicycle helmets.
For your information, that is the primary safety mechanism for a helmet. Why am I getting the idea
that you work for Giro?
> Your final conclusion that a helmet is only good for preventing
minor
> injuries and not serious injuries is a completely unquantified
conclusion
> that lacks any data and does not even feel intuitively correct.
Intuitive huh? So you have studied the matter and worked out the numbers? Try looking at the
following:
The pattern of injury in fatal pedal cycle accidents and the possible benefits of cycle helmets
Kennedy. British Journal of Sports Medicine Vol 30 pp130-3, 1996.
Examination of 28 cyclists deaths over 15 years in Sheffield and Barnsley. Over 80% of both cases
and controls had severe head injuries, but controls (an equal number of pedestrians and motor
vehicle occupant fatalities) suffered more fatal injuries to other parts of the body. If helmets had
saved all those who only had head injuries, at best 14 (50%) of cyclist deaths would have been
prevented. On the other hand, if pedestrians and vehicle occupants had worn helmets, 175 lives may
have been saved in the same period. No justification for compelling cyclists to wear helmets without
taking steps to improve safety of all road users. [j983]
Trends in cycle injury in New Zealand under voluntary helmet use Scuffham, Langley. Accident
Analysis and Prevention, Vol 29:1, 1997
An ecological analysis of serious head and non-head injuries to cyclists, and helmet wearing survey
data, 1989 to 1992 (prior to introduction of NZ manadatory helmet law). Helmet wearing rates
increased over period from 46% to 84% for primary schoolchildren, 23% to 62% for secondary
schoolchildren, and 21% to 39% for adults. All serious injuries to cyclists decreased substantially
for children, but not for adults. Serious head injuries as a percentage of all serious injuries
remained constant for all groups, with no apparent difference between bicycle-only and motor vehicle
related crashes. However, percentages of mild concussions and lacerations to the scalp decreased
more than other cyclist head injuries. The failure to achieve the expected decline in serious head
injury could be attributable to a variety of factors, including the incorrect fitting and wearing of
the helmet. Cycle use declined over the study period by 19%. [j985s]
The cost-effectiveness of compulsory bicycle helmets in New Zealand Hansen, Scuffham. Australian
Journal of Public Health Vol 19:5 pp450-4, 1995
Efficacy of helmets in protecting cyclists in New Zealand may be considerably less than predicted by
other studies.Cost of helmets per life saved varies from $88,379 for primary school children to
$1,014,850 for adults. By comparison, avoided hospital costs range from $3,304 to $56,035. [j984]
Yeah, it sure makes a lot of sense for there to be over a million dollars poured into helmets per
life saved. Some really effective cost management there alright.
Oh, by the way, if DOT came into this discussion we would wipe up the floor with them as has been
done in the past. Try reading the following:
Get a head start Which?, journal of The Consumers' Association, pp 28 - 31, October 1998.
Performance tests of cycle helmets, all produced to meet international standards. 14 of the 24
helmets failed the test criteria for shock absorption, and two of the remainder failed tests related
to retention and strap strength. Only two of the 24 helmets met the more demanding Snell standard,
and one of those caused some impairment of a cyclist's vision. [j980]
So, you see, even though helmets are bearly capable of having any effect in a collision, most of the
helmets made don't even meet that lax standard.
