Re: Helmet Wankers

[Just zis Guy, you know?]

On Sun, 8 Feb 2004 20:08:43 -0000, "Tony Raven"
<[email protected]> wrote in message
<[email protected]>:

>http://www.bhsi.org/hodgstud.htm

Interesting. I was recently told that the mechanism by which helmets
absorb energy is plastic deformation, which is why the Snell standards
specify the helmet must not break. Apparently if a helmet breaks this
is an indication that it has moved from plastic deformation to brittle
failure, a mode in which it absorbs virtually no energy. So all those
cracked helmets which "saved people's lives" actually simply failed!

Guy
===
May contain traces of irony. Contents liable to settle after posting.
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[Dave Kahn]

On Sun, 08 Feb 2004 21:37:59 +0000, "Just zis Guy, you know?"
<[email protected]> wrote:

>Interesting. I was recently told that the mechanism by which helmets
>absorb energy is plastic deformation, which is why the Snell standards
>specify the helmet must not break. Apparently if a helmet breaks this
>is an indication that it has moved from plastic deformation to brittle
>failure, a mode in which it absorbs virtually no energy. So all those
>cracked helmets which "saved people's lives" actually simply failed!

Guy, do you know of a clear reference to this? IOW a concise
authoritative statement that a shattered helmet is a failed helmet?

I've come across plenty of photos of broken or chipped helmets along
with descriptions of how the helmet saved someone's life. If the
helmets actually failed that suggests that not only did they not save
the lives in question, but that they failed in a relatively trivial
incident.

--
Dave...

Get a bicycle. You will not regret it. If you live. - Mark Twain

 

[David Kerber]

In article <[email protected]>, junk@raven-
family.com says...
> David Kerber wrote:
> >
> > That's an interesting study, but based on their descriptions, I'm not
> > sure it applies to most bicycle helmets that people actually wear. They
> > didn't describe in much detail what a "non-shell" helmet is, which they
> > noted was the only one which gave significant rotational force to the
> > head. Would that be the leather style ones which you used to see on
> > racers? Their description of "ribbed hard-shell" helmets seems to be
> > consistent with the description of the ones most riders wear these days.
>
> Hardshell is one like a motorbike helmet, microshell is what most of of are
> used to with the thin glossy plastic outer layer and non-shell is the old
> style bare polystyrene. Another interesting paper is

For hard shell, I was also thinking of the ones BMX riders wear. I
don't remember ever seeing a bare polystyrene helmet. The slick outer
covering on current helmet designs seems unlikely to "catch" on pavement
unless some kind of object (sewer grate, curb edge, car mirror?) grabs
one of the ventilation holes.

> http://www.bhsi.org/hodgstud.htm. They say the 4500r/s/s is not exceeded on
> any of the helmets but also their maximum speed is 6.4mph. If you look at the
> traces near the end they are not that much below the limit to consider you
> would stay within the limits at not much higher speeds. There is no control
> data though on the bare human head. Its also noticeable that the vented
> helmets they show have virtually no vents compared with today. It could do
> with an updated study with current helmet designs.

Sounds like it.

--
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Fight spam: remove the ns_ from the return address before replying!

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[Just zis Guy, you know?]

"Dave Kahn" <[email protected]> wrote in message
news:[email protected]...

> >I was recently told that the mechanism by which helmets
> >absorb energy is plastic deformation, which is why the Snell standards
> >specify the helmet must not break. Apparently if a helmet breaks this
> >is an indication that it has moved from plastic deformation to brittle
> >failure, a mode in which it absorbs virtually no energy. So all those
> >cracked helmets which "saved people's lives" actually simply failed!

> Guy, do you know of a clear reference to this? IOW a concise
> authoritative statement that a shattered helmet is a failed helmet?

I am trying to get one. The source was not a public one, but there must be
some public-domain references I can quote. My contacts have been, er,
contacted. Like I said, it is something I was only recently told.

--
Guy
===

WARNING: may contain traces of irony. Contents may settle after posting.
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[W K]

"Nick Maclaren" <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>,
> David Kerber <ns_dkerber@ns_ids.net> wrote:

> >Do you have any cites for the claim that helmets "amplify the rotational
> >component" of a head impact to any significant degree? I don't need to
> >see them for the fact that rotational acclerations are more damaging to
> >the brain; that is well-known, and has been for many years.
>
> I haven't seen any analyses of experimental data, though I have heard
> that there may have been a little for motorcyclists and/or horse
> riders. It is, however, immediate from the physics involved that they
> are very LIKELY to do that.
>
> Most accidents involving reasonably cautious cyclists have the cyclist
> coming off sideways - even being hit from behind at a fairly low
> relative speed will do that. If someone comes off sideways, the impact
> is on hip, shoulder and sometimes knee and elbow. Because a helmet
> increases both the width and the moment of the head by a significant
> factor, it is very likely to cause head/helmet contact where it would
> not otherwise have happened. Q.E.D.

Only by about 20% and there is a far less friction between shell/road and
head/road.
So not QED.

 

[marc]

David Kerber <ns_dkerber@ns_ids.net> wrote:

> Do you have any cites for the claim that helmets "amplify the rotational
> component" of a head impact to any significant degree?

2PiR ?


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[Steve]

Apparently if a helmet breaks this
>> >is an indication that it has moved from plastic deformation to brittle
>> >failure, a mode in which it absorbs virtually no energy. So all those
>> >cracked helmets which "saved people's lives" actually simply failed!
>

This "conclusion" conveniently ignores the energy expended during the
plastic deformation phase prior to the breakup. The aim would be to absorb
as much energy as possible b4 breakup - if the energy level exceeds that of
course it WILL break. It has still reduced the impact energy on the head.

One might as well suggest that since your suspension "bottoms out" on really
big bumps once in a while, you might as well have no suspension at all.....

I used to avoid wearing a helmet, but my intelligence finally overtook my
ego.

 

[burt]

"Steve" <[email protected]> wrote in message
news:[email protected]...
>
> I used to avoid wearing a helmet, but my intelligence finally overtook my
> ego.
>
> um, no.

 

[Ian Smith]

On Tue, 10 Feb 2004 13:01:44 +1100, Steve <[email protected]> wrote:
> >> >Apparently if a helmet breaks this
> >> >is an indication that it has moved from plastic deformation to brittle
> >> >failure, a mode in which it absorbs virtually no energy. So all those
> >> >cracked helmets which "saved people's lives" actually simply failed!
> >
>
> This "conclusion" conveniently ignores the energy expended during the
> plastic deformation phase prior to the breakup. The aim would be to absorb
> as much energy as possible b4 breakup - if the energy level exceeds that of
> course it WILL break. It has still reduced the impact energy on the head.

No, because had there been any energy in _PLASTIC_ deformation, the
bits picked up afterwards would be crushed, and the the anecdotes
typically describe helmets cracked _without_ significant plastic
distortion.

regards, Ian SMith
--
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|o o|
|/ \|

 

[Tom Kunich]

"Steve" <[email protected]> wrote in message
news:[email protected]...
> Apparently if a helmet breaks this
> >> >is an indication that it has moved from plastic deformation to brittle
> >> >failure, a mode in which it absorbs virtually no energy. So all those
> >> >cracked helmets which "saved people's lives" actually simply failed!
>
> This "conclusion" conveniently ignores the energy expended during the
> plastic deformation phase prior to the breakup.

Maybe you missed the part above where it said "brittle failure, a mode in
which it absorbs virtually no energy." If so you will note that breaking a
helmet doesn't absorb very much energy. This is a COMMON mode of helmet
failure and contrary to your visualization, it doesn't absorb very much
energy BEFORE it starts to break up.

Think about this - when a helmet is working under perfect conditions it
hardly works at all. Reducing it's ability by 60 or 70 percent sure as hell
isn't going to improve matters even when you do mention that it is better
than nothing.

> I used to avoid wearing a helmet, but my intelligence finally overtook my
> ego.

It ain't a matter of ego. I suggest that you're the one exhibiting ego if
you think that your choice to wear a helmet is any better, intelligent or
more effective than the guy who chooses otherwise.

That's the whole point here. Maybe there's some small collection of accident
types in which helmets offer an effective solution to saving your head from
getting knocked around. But there is pretty obviously another spectrum of
accidents in which wearing a helmet leads to more accidents, more serious
accidents or redirects one type of accident into another type of accident in
which a person is injured or killed. The statistics are pretty plain that
helmet wearing doesn't change the numbers or severity of head injuries.

 

[Mark Thompson]

> That's the whole point here. Maybe there's some small collection of accident
> types in which helmets offer an effective solution to saving your head from
> getting knocked around.

A large collection - they'll be oodles and scroodles of minor knocks and
headbutts that the helmet helps with. Only problem is that these don't produce
KSIs, which is what the legislation is seeking to prevent.


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[Just zis Guy, you know?]

On Tue, 10 Feb 2004 13:01:44 +1100, "Steve" <[email protected]>
wrote in message <[email protected]>:

>This "conclusion" conveniently ignores the energy expended during the
>plastic deformation phase prior to the breakup. The aim would be to absorb
>as much energy as possible b4 breakup - if the energy level exceeds that of
>course it WILL break. It has still reduced the impact energy on the head.

Fine - so the helmet goes into an unplanned failure mode at some
unknown point in its plastic deformation phase - in other words it did
not work as designed. I am happy to leave it at that.

>One might as well suggest that since your suspension "bottoms out" on really
>big bumps once in a while, you might as well have no suspension at all.....

So suspension irons out the triival bumps, but hit a really big one
and you'll get a big hit back through the arms? Hmmm, where have I
heard something like that before... ;-)

Guy
===
May contain traces of irony. Contents liable to settle after posting.
http://chapmancentral.demon.co.uk

88% of helmet statistics are made up, 65% of them at the University of Washington.

 

[the Baker-Bealls]

"Just zis Guy, you know?" <[email protected]> wrote in message
news:[email protected]...
> "Nick Maclaren" <[email protected]> wrote in message
> news:[email protected]...
>
> > Helmets almost certainly reduce trivial head injuries in all
> > classes of cyclist - i.e. mere bruises, cuts and so on. Yes,
> > some of the cuts may have needed hospital treatment, but they
> > are STILL trivial.
> >
> > Helmets almost certainly make a negligible difference to the
> > incidence of brain damage following an accident for normal
> > cyclists, and the data are not good enough to tell whether the
> > difference is positive or negative.
> >
> > Helmets probably help with extreme cycling - crashes at speeds
> > above 30 MPH, people who ride over broken rock and so on - the
> > evidence is very scanty and hence inconclusive, but is at least
> > fairly consistent.
> >
> > Mandatory and even semi-mandatory helmet wearing reduces the
> > number of normal cyclists significantly, especially those that
> > are using cycling as a form of transport rather than recreation.
> > And 'significantly' is of the order of tens of percent.
> >
> > The rest is politics, dogma and so on.
>
>
>
> On the face of it it's hard to add anything to that, other than that I
> believe the evidence indicates that cyclists wearing helmets have a
greater
> propensity to risk-taking (risk compensation).
>
> The helmet issue also affects the perception of the risk of cycling by
> drivers, such that they are likely to attribute the death of a cyclist
> wrongly as the consequence of cycling being a dangerous activity, when the
> reality is that it's driving that's dangerous. What a horrible sentence.
I
> think you know what I mean, though.
>
> --
> Guy
> ===
>
> WARNING: may contain traces of irony. Contents may settle after posting.
> http://www.chapmancentral.co.uk
>

Could risk compensation apply to the motorist rather than the cyclist? If a
driver sees you wearing a helmet is he/she likely to take greater risks with
your safety? It would certainly be a study worth doing.

Julia

 

[Tom Kunich]

"Mark Thompson" <[email protected] (change warm for hot)>
wrote in message news:[email protected]...
> > That's the whole point here. Maybe there's some small collection of
accident
> > types in which helmets offer an effective solution to saving your head
from
> > getting knocked around.
>
> A large collection - they'll be oodles and scroodles of minor knocks and
> headbutts that the helmet helps with. Only problem is that these don't
produce
> KSIs, which is what the legislation is seeking to prevent.

I didn't want to bring it up but one of the guys in the club had a minor
accident in which he went to turn right because he thought the guy he was
riding next to was going to turn right. Then clashed and he fell at slow
speed and fell into a fence.

He was just arguing with me that the helmet saved his life when the other
guy that was there explained to me that our friend's helmet caught in a
cyclone fence and that broke his neck The witness is an person with accident
experience. I forget whether he is a fireman or cop.

It all ends happily since our member was in a halo for several months and
has apparently recovered without complication.

I doubt he would have broken his neck had he not been wearing a helmet.

I think you are probably correct that a helmet can prevent oogles of very
minor injuries and if that is your intent then you are thinking well. But
let's remember that you ass is grass helmet or no in a bad accident. If your
helmet encourages you to ride more dangeously than you would without DON'T
WEAR IT.

 

[Tom Kunich]

"the Baker-Bealls" <[email protected]> wrote in message
news:[email protected]...
>
> Could risk compensation apply to the motorist rather than the cyclist? If
a
> driver sees you wearing a helmet is he/she likely to take greater risks
with
> your safety? It would certainly be a study worth doing.

Motorists seem to be at fault about half the time regardless of any other
variable if I've read the reports correctly.

 

[Steve]

Tom Kunich wrote in message ...
>"Steve" <[email protected]> wrote in message
>news:[email protected]...
>> Apparently if a helmet breaks this
>> >> >is an indication that it has moved from plastic deformation to
brittle
>> >> >failure, a mode in which it absorbs virtually no energy. So all
those
>> >> >cracked helmets which "saved people's lives" actually simply failed!
>>
>> This "conclusion" conveniently ignores the energy expended during the
>> plastic deformation phase prior to the breakup.
>
>Maybe you missed the part above where it said "brittle failure, a mode in
>which it absorbs virtually no energy." If so you will note that breaking a
>helmet doesn't absorb very much energy. This is a COMMON mode of helmet
>failure and contrary to your visualization, it doesn't absorb very much
>energy BEFORE it starts to break up.
>
Actually I noticed that it said "...has moved from plastic deformation to
brittle...." so I took it that both phases occured, buthe second brittle
phase didn't absorb much energy.
>Think about this - when a helmet is working under perfect conditions it
>hardly works at all. Reducing it's ability by 60 or 70 percent sure as hell
>isn't going to improve matters even when you do mention that it is better
>than nothing.
>
>> I used to avoid wearing a helmet, but my intelligence finally overtook my
>> ego.
>
>It ain't a matter of ego. I suggest that you're the one exhibiting ego if
>you think that your choice to wear a helmet is any better, intelligent or
>more effective than the guy who chooses otherwise.
>
Interesting thought. I suppose ego is what drives people to bother with
posting That was my personal feeling about why I started wearing a
helmet.

>That's the whole point here. Maybe there's some small collection of
accident
>types in which helmets offer an effective solution to saving your head from
>getting knocked around. But there is pretty obviously another spectrum of
>accidents in which wearing a helmet leads to more accidents, more serious
>accidents or redirects one type of accident into another type of accident
in
>which a person is injured or killed. The statistics are pretty plain that
>helmet wearing doesn't change the numbers or severity of head injuries.
>
That's surprising - & interesting - have you got some studies/references we
can peruse?
ta
Steve

 

[burt]

"the Baker-Bealls" <[email protected]> wrote in message
news:[email protected]...
>
>
> Could risk compensation apply to the motorist rather than the cyclist? If
a
> driver sees you wearing a helmet is he/she likely to take greater risks
with
> your safety? It would certainly be a study worth doing.
>
> Julia
>

I have certainly read something which supports this. CTC member riding in
the US wrote that many drivers gave them more room than helmeted riders,
with some taking extreme measures to avoid them.
>

 

[Tom Kunich]

"Steve" <[email protected]> wrote in message
news:[email protected]...
> Tom Kunich wrote in message ...
> >The statistics are pretty plain that
> >helmet wearing doesn't change the numbers or severity of head injuries.
> >
> That's surprising - & interesting - have you got some studies/references
we
> can peruse?

http://www.magma.ca/~ocbc/hfaq.html

http://www.magma.ca/~ocbc/kunich.html

http://www.helmets.org/veloaust.htm

http://www.magma.ca/~ocbc/scuffham.html

Scuffham is the most important since it was a study done by a group who were
pro-helmet and unabashedly say that they intended to find a positive effect
for helmet use and instead no matter how they manipulated the data it showed
no effects. A later 're-interpretation' using complex mathematical methods
claims to have found a very slightly positive effect. That an $2.95 will get
you a Latte' at Starbucks.