Inflatable helmet, really

On 9/10/2010 3:49 PM, !Jones wrote:
[...] Now, how do you think I feel about Jane Fonda? [...]

Who? Ted Turner's ex-wife?

--
Tom Sherman - 42.435731,-83.985007
I am a vehicular cyclist.

On 9/10/2010 1:46 AM, Mike Why? What? Where? When? Who? How? wrote:
Tom Sherman °_° wrote:
On 9/9/2010 10:51 PM, Frank Krygowski wrote:
On Sep 9, 8:37 pm, "MikeWhy" wrote:
Phil W Lee wrote:

Utter bull****.
If cycle helmets met the same standards, don't you think some
motorcyclists would be wearing them?

Not bull****. Look it up if you can figure out Google. Motorcycle
helmets have additional criteria not specified for bicycle
helmets, including coverage area and involving the chin bar when
present. Retention criteria are also more stringent. Impact loads
and survivability, however, are essentially the same.
A funny thing happens when one actually looks up what MikeWhy claims.
Specifically, they find that MikeWhy is either mistaken or lying.

Here's an article that discusses motorcycle helmet testing standards
in detail. (I've got it bookmarked.)
http://www.motorcyclistonline.com/ge...iew/index.html

or http://tinyurl.com/zglbq

What it says? "The killer—the hardest Snell test for a motorcycle
helmet to meet—is a two-strike test onto a hemispherical chunk of
stainless steel about the size of an orange. The first hit is at an
energy of 150 joules, which translates to dropping a 5-kilo weight
about 10 feet—an extremely high-energy impact. The next hit, on the
same spot, is set at 110 joules, or about an 8-foot drop. To pass,
the helmet is not allowed to transmit more than 300 Gs to the
headform in either hit."

Later, it says: "Where the Snell standard limits peak linear
acceleration to 300 G, the DOT effectively limits peak Gs to 250.
Softer impacts, lower G tolerance. In short, a kinder, gentler
standard."

I'm not sure about that "effectively." According to
http://www.smf.org/articles/mcomp2.html
DOT limits acceleration to 400 gs, but from a drop height (for a
large helmet) of about 7.35 feet, or 2.25 meters, which corresponds
to 110 Joules for a 5 kg headform mass.

By contrast, the CPSC bicycle helmet standard calls for just a two
meter drop. It allows 300 gs acceleration of the same headform. The
standards are NOT the same.

Furthermore, the motorcycle helmet standard has much more rigid
penetration tests. This is what drives the design of their heavy,
hard shells. And this is pertinent, because a heavy, hard shell is
less likely to get traction with the road during a tangential impact,
and is more likely to have significant rotational inertia, to aid in
reducing the brain's rotational acceleration. This might be
considered an accidental benefit, because penetration of any helmet
is rare, but rotational brain accelerations are now commonly
recognized as being more likely than linear ones to cause serious
brain injury. (Still, NO helmet standard tests for them!)

What's even more enlightening is that article's discussion of the
effect of various acclerations: "Newman is quoted in the COST study
on the impact levels likely to cause certain levels of injury. Back
in the '80s he stated that, as a rough guideline, a peak linear
impact— the kind we're measuring here&151of 200 to 250 Gs generally
corresponds to a head injury of AIS 4, or severe; that a 250 G to 300
G impact corresponds to AIS 5, or critical; and that anything over
300 Gs corresponds to AIS 6. That is, unsurvivable."

Bike helmets are designed to attenuate the acceleration of a
decapitated human head - no body attached - to 300 gs in a 14 mph
impact. 300 gs is the borderline between critical and unsurvivable,
according to that estimate. And that doesn't take into account
rotational acceleration, which is worse in its effect, and which
helmets may exacerbate (by their larger diameter and higher friction
compared to a bare head).

So leave the cyclist's head attached to his body, subject him to a
head impact greater than 14 mph, include a slight tangential
component to the impact, and you've blown away the "protection" of a
bike helmet.

Is it any wonder they haven't been shown to reduce serious head
injuries?

Dear Frank,

Please stop confusing the Liddites™ with facts - it only makes them
angry that their religious belief in the Magic Foam Bicycle Hat™ is
challenged.

Actually, it's the facts that make you, not me, cringe, run, hide, and
blow smoke.

Male bovine excrement.

The only agenda *I* have is to counter the misinformation
spewed here about helmet ineffectiveness.

No, you are a foam bicycle hat promoter.

There are factual errors and
errors of logic in Frank's post above. I won't address them
individually.

I.e., I cannot.

To do so would be to spend the rest of eternity talking at
insensate and unlearning furniture.

I sense projection here.

The facts of the matter are these:

[...]
You can work through the rest of it yourself, given this proper picture
of what the impact test really entails. Bearing in mind that a helmet
worn on the head does nothing for the neck or its attachment to the
head, just what does it mean to substitute the full body mass, as Frank
suggests, for the head mass in the test? I intended that as gently
rhetorical, but it would be interesting to hear further defense of his
oddly blind suggestions.

Gee, you would think having the body attached to the head is usual in an
accident? If decapitation occurs, how the head fares is really
meaningless, no?

--
Tom Sherman - 42.435731,-83.985007
I am a vehicular cyclist.

On Fri, 10 Sep 2010 22:00:48 +0100, in rec.bicycles.tech Clive George
wrote:

For somebody who's denying writing about helmets is their thing, you
sure do write a lot.

Well, you said that you wanted to have a discussion, didn't you?
OK... I usually write in complete sentences and I develop my points.
My points, here, really have nothing to do with helmets. In *that*
area, I'm willing to accept a preponderance of evidence and a general
consensus of medical professionals. JAMA has pretty well made their
statement, so I'll go with that. If you don't, then that's OK with
me.

Jones

On Fri, 10 Sep 2010 17:20:02 -0500, in rec.bicycles.tech Tom Sherman
°_° wrote:

[...] Now, how do you think I feel about Jane Fonda? [...]

Who? Ted Turner's ex-wife?

No, Barbarella.

On 9/10/2010 6:34 PM, !Jones wrote:
On Fri, 10 Sep 2010 17:20:02 -0500, in rec.bicycles.tech Tom Sherman
wrote:

[...] Now, how do you think I feel about Jane Fonda? [...]

Who? Ted Turner's ex-wife?

No, Barbarella.

Stone Age.

--
Tom Sherman - 42.435731,-83.985007
I am a vehicular cyclist.

On Fri, 10 Sep 2010 18:57:21 -0500, in rec.bicycles.tech Tom Sherman
°_° wrote:

No, Barbarella.

Stone Age.

Agreed; however, she had some nice knockers back then. Time and
tide... you know.

Jones

it gets only worser

On Sep 10, 4:59*pm, James wrote:
On Sep 11, 1:35*am, Frank Krygowski wrote:

On Sep 10, 3:07*am, James wrote:
Also, has anyone actually dabbed their head on the ground while
traveling along, to try to gauge the applied torque produced comparing
a bare head to a bicycle helmeted one?

I don't know of a test for the effective friction coefficient of a
bare human head subjected to a tangential force from an asphalt
surface. *I suspect, though, that the coefficient is much lower than
that of a helmet in the same situation.

Maybe your Unliddedness has let your eyesight degrade. *I posted a
link. *MikeWhy found it. *Strangely you overlooked it. *Maybe, like so
much else you didn't like the message it brought and chose to sweep it
under the carpet and respond with more rubbish.

What utter bull****! Did you even bother to read that paper? There
was no mention anywhere in the paper of the coefficient of friction of
a bare head on pavement in a typical crash.

While I'm at it, the paper - intended to show that most helmets won't
impart too much rotational acceleration - tested impacts at a
_maximum_ speed of less than 9 mph, to protect the crash test dummy.
Much of its data was gathered at only 6.5 mph, and some even lower.
There is no evidence its measurements are valid at any higher speed.

For example, the only coefficient of friction stated was measured by a
static test, tilting the road surface until sliding ensued. But would
this really be the effective coefficient in an impact of a helmet at
higher velocity? Unlikely, because the helmet would likely deform and
interlock with the road surface's roughness, much like a drag racer's
slicks interlock with asphalt, giving an effective coefficient far
greater than 1.0

Now, would such interlocking be more likely at higher velocities -
say, the still-inadequate 14 mph of a standard helmet impact test?
Almost certainly! But this test didn't even come close to that low
velocity. Again, much of the data comes from an impact less than half
as great - an impact speed of just 6.5 mph. That corresponds to a
drop height of just 17 inches! Isn't it likely that in more severe
impacts, the interlocking, the effective coefficient of friction, and
the angular acceleration would be much greater?

More briefly, that test is claiming that what works in a 17" drop will
work just as well in a real bike crash. It's nonsense.

BUT! If you are on board with that test's results, I assume you also
approve of the recommendation to fit clear face masks to bike
helmets?

"3. Helmets for children should be equipped with a chin-bearing
faceguard for maximum protection of face, head, and neck. 4. Helmet
manufacturers should conduct research to devise an appropriate bicycle
helmet faceguard for youth and offer it in their line of protective
products."

Oh, and don't miss the place where he describes the effect of the body
mass behind the helmet. You know, the mass that's absent from the
helmet certification test, which tests only for decapitated heads?

Now: Does anybody _really_ have data on the effective coefficient of
friction of a bare head in a tangential impact against the ground?

- Frank Krygowski

helmet interlock ? now this sounds serious errrrrrrrrkkkkkk! now
wegotta worry about neck injury, spinal dislocations, cranial nerves
torn ass under. Frank, yawl related to Nadir ?

but seriously. by the time you get to the asphalt, usually covered
with hydrocarbons and itself a lubricious product of dead protoplasm,
how fast are you going ? do the math.

On 9/10/2010 9:27 PM, kolldata aka AVOGADRO V wrote:


it gets only worser

Then worstest!

--
Tom Sherman - 42.435731,-83.985007
I am a vehicular cyclist.