Cooler Helmet?

[Mike Reed]

[email protected] wrote:
> Fewer than 1% of head injury fatalities are cyclists.

What's that got to do with anything? Fewer than 1% of the people in
motion on the surface of the planet at this moment are on bicycles.

-Mike

 

[Mike Reed]

Marz wrote:
> The helmet didn't save you from brain damage your thick skull did. The
> helmet did save you from cuts and bruises, which is why I wear one
> offroad.
>
> There are severe limitations to what a helmet can and can't do. If you
> strike me with a 2*4 I would feel the full blunt impact with or without
> a helmet. A helmet might save me from a nasty scratch to the head, but
> it will also provide you with a bigger target.

A helmet is a rigid structure tha distributes a load across the pads to
differnet parts of your head. Say we strike a human head with a 2x4's
edge, with enough force to cave the skull and cause severe brain
trauma. Then, take that same force, and strike a properly fit and
adjusted helmet that is on a human head.

Which head would you prefer to be yours?

Even for blunt impacts (like a smooth road surface or a car window), a
helmet spreads the load to other parts of your head, creating a much
larger contact patch for your skull to deal with. Without a helmet, the
skull deforms to flatten out and match the impacting surface.

There's no way to protect signifcantly from brain movement within an
intact skull, but preventing any deformation of the skull is a big
help.

> A helmet can provide some protection in some instances, but not enough
> to be made compulsive by law or insurance.

I would never suggest compulsive helmet wear unless it was to ease
liability (like in a race).

-Mike

 

[Bestest Handsander]

"Marz" <[email protected]> wrote in message
news:[email protected]...
> There are severe limitations to what a helmet can and can't do. If you
> strike me with a 2*4 I would feel the full blunt impact with or without
> a helmet. A helmet might save me from a nasty scratch to the head, but
> it will also provide you with a bigger target.

I don't believe this is correct. The very fact that the helmet deforms and
cracks shows that it obsorbed some of the energy and distributed the rest to
a wider area similar to a crush zone on a car. How much it absorbs is
another question.

Let's try this. We'll drop a 100 gram steel bearing onto Carl Fogel's head
from 5 feet. Now turn him over, place the material used to make helmets on
his head, and we'll drop the same 100 gram bearing. Does the second side
sustain the same damage as the first?

 

[[email protected]]

Mike Reed wrote:
> [email protected] wrote:
> > Fewer than 1% of head injury fatalities are cyclists.
>
> What's that got to do with anything? Fewer than 1% of the people in
> motion on the surface of the planet at this moment are on bicycles.
>
> -Mike

Well, for one thing, it's common for helmet promotions to tout supposed
benefits to society ("Bicycling head injuries cost the country $480
trillion dollars per month" or such nonsense). Obviously, cycling's
contribution to any total head injury costs are negligible. You could
save roughly 50 times more of society's money by promoting car helmets,
for example.

For another thing, helmet promoters stock in trade is to tell of the
tragedies that occur because of riding without a styrofoam hat. But
such bicycling tragedies are, indeed, extremely rare. They are
outnumbered 100 to one by other equally tragic head injuries from other
sources.

But the helmet promoters never mention that. Even if they are people
who supposedly love cycling, they are willing to make cycling sound
uniquely dangerous in order to push their views.

Cycling is NOT very dangerous. It does us no good to pretend it is.

- Frank Krygowski

 

[[email protected]]

Sorni wrote:
>
> Despite your (repeated) long-winded diatribes, you miss MY point. When
> someone falls and is NOT hurt because they're wearing a helmet, no one hears
> about it. (Certainly no "data houses" or other table-type lists.)

I'll try to be briefer, in hopes you'll understand:

1991. Sample 10,000 bicyclists. Say only 1,000 wore helmets. Check
the records, and find fifty of the 10,000 fell and hit their heads hard
enough to be treated. That's data.

1992. Mandatory helmet law. Sample 10,000 cyclists. (They're harder
to find now, but keep looking until you find 10.000.) Now 8,000 wear
helmets. Check the records, and find that 50 of the total fell and hit
their heads hard enough to be treated.

IF the extra 7,000 were really being protected by helmets, the number
of injuries per 10,000 would have decreased. That's how the protected
folks would show up in the data.

If there is no reduction in the original 50, there is no significant
number of people who are "not being heard about."

That's about as simple as I can make it, except to point out that after
the mandatory helmet laws, the head injuries per 10,000 cyclists
actually rose. Numbers are, of course, approximate and by memory.
Details on request.

> It's really not that complicated.

It shouldn't be! IOW, it _should_ be that people would look at actual
large-population data to determine the real-world benefit of helmets -
or lack of same.

But most people have trouble with numbers, and fall back on stories of
2x4s and Darwin!

- Frank Krygowski

 

[[email protected]]

Bestest Handsander wrote:
>
> Let's try this. We'll drop a 100 gram steel bearing onto Carl Fogel's head
> from 5 feet. Now turn him over, place the material used to make helmets on
> his head, and we'll drop the same 100 gram bearing. Does the second side
> sustain the same damage as the first?

I have no doubt a bike helmet will protect against 100 gram ball
bearings.

But when a MHL was being promoted in our state, they told the tale of a
kid riding wrong-way on a highway, hit head on by a Chevy Blazer. They
actually claimed that if he'd been wearing a helmet, he'd have been OK.

What protects against a bearing won't help much against a Blazer.

- Frank Krygowski

 

[41]

Mike Reed wrote:
> A helmet is a rigid structure tha distributes a load across the pads to
> differnet parts of your head. Say we strike a human head with a 2x4's
> edge, with enough force to cave the skull and cause severe brain
> trauma. Then, take that same force, and strike a properly fit and
> adjuste d helmet that is on a human head.
>
> Which head would you prefer to be yours?
>
> Even for blunt impacts (like a smooth road surface or a car window), a
> helmet spreads the load to other parts of your head, creating a much
> larger contact patch for your skull to deal with. Without a helmet, the
> skull deforms to flatten out and match the impacting surface.
>
> There's no way to protect signifcantly from brain movement within an
> intact skull, but preventing any deformation of the skull is a big
> help.

No, it is not. If what you say were true, then you would be wearing a
hard-shell helmet, not a soft one with an anti-friction layer. That is
why police helmets, military helmets, baseball helmets, etc are hard
shell (often with minimal or no padding), while bicycle helmets have
maximal padding and no hard shell. Impact of a moving head with a
stationary object is an entirely different problem from impact of
moving object with stationary head. Manufacturers recognized this a
long time ago and so the change from hard shell to soft shell to soft
shell with antifriction layer.

To put it more directly: you will die from brain deceleration long
before your skull is damaged in any impact with a hard object where it
is you that moves and not the object.%

 

[Sorni]

[email protected] wrote:
> Sorni wrote:
>>
>> Despite your (repeated) long-winded diatribes, you miss MY point.
>> When someone falls and is NOT hurt because they're wearing a helmet,
>> no one hears about it. (Certainly no "data houses" or other
>> table-type lists.)
>
> I'll try to be briefer, in hopes you'll understand:
>
> 1991. Sample 10,000 bicyclists. Say only 1,000 wore helmets. Check
> the records, and find fifty of the 10,000 fell and hit their heads
> hard enough to be treated. That's data.
>
> 1992. Mandatory helmet law. Sample 10,000 cyclists. (They're
> harder to find now, but keep looking until you find 10.000.) Now
> 8,000 wear helmets. Check the records, and find that 50 of the total
> fell and hit their heads hard enough to be treated.
>
> IF the extra 7,000 were really being protected by helmets, the number
> of injuries per 10,000 would have decreased. That's how the protected
> folks would show up in the data.
>
> If there is no reduction in the original 50, there is no significant
> number of people who are "not being heard about."
>
> That's about as simple as I can make it, except to point out that
> after the mandatory helmet laws, the head injuries per 10,000 cyclists
> actually rose. Numbers are, of course, approximate and by memory.
> Details on request.
>
>> It's really not that complicated.
>
> It shouldn't be! IOW, it _should_ be that people would look at actual
> large-population data to determine the real-world benefit of helmets -
> or lack of same.
>
> But most people have trouble with numbers, and fall back on stories of
> 2x4s and Darwin!
>
> - Frank Krygowski

That was brief? LOL

If I bang my head on a curb, I hope I'm wearing a helmet.

It's really not that complicated.

BS

 

[41]

41 wrote:

> To put it more directly: you will die from brain decelerat ion long
> before your skull is damaged in any impact with a hard object where it
> is you that moves and not the object.%

Clarification: blunt object, i.e. one that will dent it rather than
penetrating it. Unfortunately non-hard shell bicycle helmets don't
protect much against penetration either, being so much softer than the
skull. Such protection was sacrificed when the hard shell was dropped,
and no one complained.>

 

[Marz]

Mike Reed wrote:
> Even for blunt impacts (like a smooth road surface or a car window), a
> helmet spreads the load to other parts of your head, creating a much
> larger contact patch for your skull to deal with. Without a helmet, the
> skull deforms to flatten out and match the impacting surface.
>
> There's no way to protect signifcantly from brain movement within an
> intact skull, but preventing any deformation of the skull is a big
> help.
> -Mike

Only up until the point of failure. Yes, if you hit me with a 2x4 and
the helmet stays intact then the helmets has done it's job and spread
the impact. But if you strike my hard enough to crack the helmet, then
the helmet has failed and most of the force you used is transfered
straight to my skull. Think of those martial art demos where nutters
try to crack towers of cinder blocks with their bare hands. The force
is transfered from block to block, but you can see the slight reduction
in force down through the tower as usually the last couple of blocks
are left intact.

So, ok even a broken helmet 'must' reduce the impact by some amount,
but I don't think that reduction is very much at all. I guess that's
the problem, I think this, you think that, doctors and engineers differ
in their opions. If someone could produce some numbers saying for
example that a helmet would reduce X amount of force in a Ymph accident
then we could move on.

Laters,

Marz

 

[Bestest Handsander]

<[email protected]> wrote in message
news:[email protected]...
>
> Bestest Handsander wrote:
>>
>> Let's try this. We'll drop a 100 gram steel bearing onto Carl Fogel's
>> head
>> from 5 feet. Now turn him over, place the material used to make helmets
>> on
>> his head, and we'll drop the same 100 gram bearing. Does the second side
>> sustain the same damage as the first?
>
> I have no doubt a bike helmet will protect against 100 gram ball
> bearings.
>
> But when a MHL was being promoted in our state, they told the tale of a
> kid riding wrong-way on a highway, hit head on by a Chevy Blazer. They
> actually claimed that if he'd been wearing a helmet, he'd have been OK.
>
> What protects against a bearing won't help much against a Blazer.

Never claimed that it would. I suggested this experiment to show only that a
helmet does reduce the force at point of impact through deformation. EVERY
protective device will fail will hit with ENOUGH force.

Your Blazer story lacks enough detail to draw a conclusion. Did the coroner
find that all other injuries were survivable, but the head injury was what
killed him? And did he concluded that in his experience a helmet would have
mitigated that? If so, then the crusaders would have a point. If not, then
they were exploiting the boy's death.

 

[G.T.]

Sorni wrote:
> G.T. wrote:
>
>>Mike Reed wrote:
>>
>>>jtaylor wrote:
>>>
>>>
>>>
>>>>Helmets don't work.
>>>
>>>
>>>Darwin works. Happy riding.
>
>
>>So you believe in the miracle that helmets will save lives? Ironic.
>
>
> Ironic? Don't you mean misguided, perhaps, or stupid or silly? (All IYO,
> of course.)
>
> But ironic?
>

Yes, ironic. As in its ironic that Darwin was mentioned by someone who
believes in miracles. Darwin was a thinking man. Personally I'm not
going to rely on a miracle to save my life.

Greg

--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

 

[G.T.]

Sorni wrote:
> [email protected] wrote:
>
>>On Thu, 27 Apr 2006 06:14:05 GMT, "Sorni"
>><[email protected]> wrote:
>>
>>[snip]
>>
>>
>>>Dear Carl,
>>>
>>>Statistics schmatistics. If I bounce my helmeted head off a curb
>>>edge and walk away a little sore but otherwise intact, there's no
>>>entry on anyone's ledger besides my own.
>>>
>>>It's really not that complicated.
>>>
>>>Bill S.
>
>
>>Dear Bill,
>>
>>Er . . .
>>
>>"Most people are at least a little more likely to lose their
>>balance on a bike (whether through clumsiness, carelessness
>>or just plain bad luck with an obstacle or blowout) than
>>when perched upon two big slabs of feet meat."
>>
>>"Percentages."
>>
>>That was you earlier in this thread, wasn't it?
>>
>>Cheers,
>>
>>Carl Fogel
>
>
> So what's your point, Carl? People who fall and hit their head but AREN'T
> aren't hurt because they were wearing a helmet don't become statistical
> figures. They get up and ride away.
>

And if they weren't wearing a helmet they'd still get up and ride away,
possibly with a cut that needed to be bandaged. It's impossible for a
bicycle helmet to prevent major brain injury.

Greg
--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

 

[G.T.]

Mike Reed wrote:
> G.T. wrote:
>
>>Mike Reed wrote:
>>
>>>jtaylor wrote:
>>>
>>>
>>>
>>>>Helmets don't work.
>>>
>>>
>>>Darwin works. Happy riding.
>>>
>>
>>So you believe in the miracle that helmets will save lives? Ironic.
>>
>>Greg
>
>
> Miracle? Adding material to increase structural stability is
> engineering, not theology. How does armor work? If we changed the term
> "bicycle helmet" to "armor," then do you think they would work better?
>
> I woke up in the hospital one day following my ride home from work, and
> found my helmet to be cracked and compressed. I was in the hospital for
> a pneumothorax caused by my broken rib. My helmet had completely
> smashed through the rear side window of the car that drove in front of
> me. I believe the helmet saved me from some serious head injuries. Even
> with the helmet, I still had a mild concussion, but the helmet
> prevented skull deformation that would have caused a more serious brain
> injury. At least that's what my neurologist told me.
>
> But WTF does he know, right? Stupid brain surgeon.

Was he a physicist, too?

>
> Let's say I go out to the local hike and bike trail and start cracking
> random cyclists over the head with a 2x4. Would it be a miracle that
> the helmetless riders would go to the hospital more than the helmeted?

Yes, for cuts and bruises.

>
> Do you think helmets don't offer protection?

Yes, from cuts and bruises.

>
> Do you think accidents don't happen where helmets prevent injury?

No, they prevent cuts and bruises.

>
> Are you sure you haven't already sustained such an injury that's
> swaying your opinion here?
>

Possibly, but it wasn't from wearing or not wearing a helmet.

Greg

--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

 

[Sorni]

G.T. wrote:
> Sorni wrote:
>> G.T. wrote:
>>
>>> Mike Reed wrote:
>>>
>>>> jtaylor wrote:
>>>>
>>>>
>>>>
>>>>> Helmets don't work.
>>>>
>>>>
>>>> Darwin works. Happy riding.
>>
>>
>>> So you believe in the miracle that helmets will save lives? Ironic.
>>
>>
>> Ironic? Don't you mean misguided, perhaps, or stupid or silly? (All IYO,
>> of course.)
>>
>> But ironic?
>>
>
> Yes, ironic. As in its ironic that Darwin was mentioned by someone
> who believes in miracles. Darwin was a thinking man. Personally I'm
> not going to rely on a miracle to save my life.

Ah, but it was you who injected the concept of "miracle" into the
discussion. (Not ironic, BTW, just misguided )

B.S.

 

[Sorni]

G.T. wrote:
> Sorni wrote:
>> [email protected] wrote:
>>
>>> On Thu, 27 Apr 2006 06:14:05 GMT, "Sorni"
>>> <[email protected]> wrote:
>>>
>>> [snip]
>>>
>>>
>>>> Dear Carl,
>>>>
>>>> Statistics schmatistics. If I bounce my helmeted head off a curb
>>>> edge and walk away a little sore but otherwise intact, there's no
>>>> entry on anyone's ledger besides my own.
>>>>
>>>> It's really not that complicated.
>>>>
>>>> Bill S.
>>
>>
>>> Dear Bill,
>>>
>>> Er . . .
>>>
>>> "Most people are at least a little more likely to lose their
>>> balance on a bike (whether through clumsiness, carelessness
>>> or just plain bad luck with an obstacle or blowout) than
>>> when perched upon two big slabs of feet meat."
>>>
>>> "Percentages."
>>>
>>> That was you earlier in this thread, wasn't it?
>>>
>>> Cheers,
>>>
>>> Carl Fogel
>>
>>
>> So what's your point, Carl? People who fall and hit their head but
>> AREN'T aren't hurt because they were wearing a helmet don't become
>> statistical figures. They get up and ride away.
>>
>
> And if they weren't wearing a helmet they'd still get up and ride
> away, possibly with a cut that needed to be bandaged. It's
> impossible for a bicycle helmet to prevent major brain injury.

Years ago on a local mtb ride, I got bouncing in a rock (baby heads) garden
and did a spectacular endo. Banged my head HARD on a very hard rock. I got
up and finished the ride.

I'm not saying I would have had "major brain injury" necessarily, but I'm
pretty damned sure I would have had a serious concussion or perhaps even a
fractured skull. I'm absolutely certain that I would NOT have gotten up and
completed the ride; best case might have been a very slow walk back to the
trail head and a ride home (or to the hospital) from one of the guys with
me.

It's really not that complicated.

B.S.

(And PS: Carl was trying to equate statistics with
percentages/probabilities. Ain't the same.)

 

[[email protected]]

On Thu, 27 Apr 2006 10:16:29 -0600, "Bestest Handsander"
<[email protected]> wrote:

>"Marz" <[email protected]> wrote in message
>news:[email protected]...
>> There are severe limitations to what a helmet can and can't do. If you
>> strike me with a 2*4 I would feel the full blunt impact with or without
>> a helmet. A helmet might save me from a nasty scratch to the head, but
>> it will also provide you with a bigger target.
>
>I don't believe this is correct. The very fact that the helmet deforms and
>cracks shows that it obsorbed some of the energy and distributed the rest to
>a wider area similar to a crush zone on a car. How much it absorbs is
>another question.
>
>Let's try this. We'll drop a 100 gram steel bearing onto Carl Fogel's head
>from 5 feet. Now turn him over, place the material used to make helmets on
>his head, and we'll drop the same 100 gram bearing. Does the second side
>sustain the same damage as the first?

Dear BH,

To take the old chestnut about settling the matter by
whacking each other with baseball bats . . .

I'd ask to go without a helmet--and to go first.

Then I'd reluctantly kill my opponent. A good swing with a
30-ounce bat is likely to break a neck, never mind what
happens to the brain inside the skull and styrofoam.

To get an idea of what kind of impact a baseball bat
involves:

http://www.kettering.edu/~drussell/bats-new/impulse.htm

The bat moves much faster than a car or head attached to a
body, but it also weighs far less. The very existence of the
old I'll-prove-it-with-a-bat argument shows how little most
of us actually think about the damnably stubborn physics
involved.

Typical fatal and serious head injuries in bicycle accidents
involve masses, velocities, and impacts far beyond the
protective effect of a styrofoam half-shell.

That's why the helmet manufacturers make no claims of
protection and why the helmet tests involve impacts no
greater than dropping straight down five feet, which is
practically impossible with a bicycle between your legs.

As worked out before on RBT, toppling sideways in any
direction is likely to produce a greater impact speed than a
straight drop--the end of a toppling column strikes the
ground at 3/2 the speed it would if dropped in free-fall
from the same height. No helmets are certified to prevent
injury for the kind of impact you experience if you topple
over sideways at the stop-light.

The technical question about whether helmets reduce serious
and fatal head injuries invariably winds up in the same
places.

Statistically, increased helmet use has no apparent effect
on nation-wide injury rates. Either helmets don't offer the
protection that we hope for, or else they do offer it, but
we promptly ride more dangerously (a theory that sounds
silly, but which has a dreadfully convincing history of
testing and theory behind it in numerous other cases), or
else the nation-wide statistics are artfully fudged at just
the right rate to hide everything, year after year.

Physically, there's not much hope for justifying the effect
that we all want to see. I don't like it, but many of us are
hoping and arguing that paint-ball armor would offer
significant protection from gunfire.

Cheers,

Carl Fogel

 

[Bestest Handsander]

"41" <[email protected]> wrote in message
news:[email protected]...
>
> Mike Reed wrote:
>> A helmet is a rigid structure tha distributes a load across the pads to
>> differnet parts of your head. Say we strike a human head with a 2x4's
>> edge, with enough force to cave the skull and cause severe brain
>> trauma. Then, take that same force, and strike a properly fit and
>> adjuste d helmet that is on a human head.
>>
>> Which head would you prefer to be yours?
>>
>> Even for blunt impacts (like a smooth road surface or a car window), a
>> helmet spreads the load to other parts of your head, creating a much
>> larger contact patch for your skull to deal with. Without a helmet, the
>> skull deforms to flatten out and match the impacting surface.
>>
>> There's no way to protect signifcantly from brain movement within an
>> intact skull, but preventing any deformation of the skull is a big
>> help.
>
> No, it is not. If what you say were true, then you would be wearing a
> hard-shell helmet, not a soft one with an anti-friction layer. That is
> why police helmets, military helmets, baseball helmets, etc are hard
> shell (often with minimal or no padding), while bicycle helmets have
> maximal padding and no hard shell. Impact of a moving head with a
> stationary object is an entirely different problem from impact of
> moving object with stationary head. Manufacturers recognized this a
> long time ago and so the change from hard shell to soft shell to soft
> shell with antifriction layer.
>
> To put it more directly: you will die from brain deceleration long
> before your skull is damaged in any impact with a hard object where it
> is you that moves and not the object.%

A little knowledge.... Motorcycle helmets are designed by mandate to
withstand multiple impacts. Bicycle helmets are designed to withstand a
single impact.

Why is that important? Because a helmet protects two ways. It deforms and
breaks apart thus decelerating the head over a longer period of time
decreasing the amount of Gs that slosh the yoke around. It also spreads the
force on the point of impact over a larger area thus giving the shell more
protection from fracture.

Years ago there was a big debate in motorcycle circles about this. Some
argued that making a helmet more rigid to withstand multiple impacts
increased the severity of brain trauma on single impact because it didn't
break ENOUGH. The other side argued that multiple impacts were far more
common than single impacts, and helmets should continue to be designed to
withstand more than one.

Of interest to us is that both sides of that debate agreed on HOW a helmet
protects. They were simply arguing which type of accident was most common.

I saw a show on the science channel a few years ago where students had to
build design and build something that would protect an egg from breaking
when thrown off a tall building. Guess what design won? The one that wrapped
the egg in layers of Styrofoam that almost completely shattered when it hit
the ground, BUT the egg didn't break! Go figure.

 

[[email protected]]

On 27 Apr 2006 08:18:43 -0700, [email protected] wrote:

>
>[email protected] wrote:
>>
>> The text description is dramatic, and we're all relieved
>> that Mark wasn't hurt worse, and angry at the truck driver
>> fr nearly killing him.
>
>This is a bit off-topic, but it seems Mark would have no reason to be
>angry at the truck driver. It wasn't the truck driver who nearly
>killed Mark. It was Mark who nearly suicided.

[snip]

Dear Frank,

Alas, trying to be objective about helmets strains my feeble
character to the limits. I desperately want to believe that
my yellow helmet will save me, no matter what physics and
statistics say.

(My desperation is silly, given how safe bicycling is.)

Two wheels good! Four wheels bad!

(I become more reasonable when driving.)

Cheers,

Napoleon

 

[41]

Bestest Handsander wrote:
> "41" <[email protected]> wrote in message
> news:[email protected]...
> >
> > Mike Reed wrote:

> >> There's no way to protect signifcantly from brain movement within an
> >> intact skull, but preventing any deformation of the skull is a big
> >> help.
> >
> > No, it is not. If what you say were true, then you would be wearing a
> > hard-shell helmet, not a soft one with an anti-friction layer. That is
> > why police helmets, military helmets, baseball helmets, etc are hard
> > shell (often with minimal or no padding), while bicycle helmets have
> > maximal padding and no hard shell. Impact of a moving head with a
> > stationary object is an entirely different problem from impact of
> > moving object with stationary head. Manufacturers recognized this a
> > long time ago and so the change from hard shell to soft shell to soft
> > shell with antifriction layer.
> >
> > To put it more directly: you will die from brain deceleration long
> > before your skull is damaged in any impact with a hard object where i t
> > is you that moves and not the object.%
>
> A little knowledge.... Motorcycle helmets are designed by mandate to
> withstand multiple impacts. Bicycle helmets are designed to withstand a
> single impact.
>
> Why is that important? Because a helmet protects two ways. It deforms and
> breaks apart thus decelerating the head over a longer period of time
> decreasing the amount of Gs that slosh the yoke around. It also spreads the
> force on the point of impact over a larger area thus giving the shell more
> protection from fracture.

The point is that in the case of the human head, long before the skull
breaks from impacts as described above, death occurs due to brain
deceleration inside the skull. The anti-friction layer in current
helmets also serves or is intended to serve the function of keeping the
helmet together for multiple impacts, a function previously served in
soft shell helmets by a net/ helmet cover. These were explicit design
considerations, regardless of the Snell or ANSI standards, after just
such failures with plain soft shells.


> I saw a show on the science channel a few years ago where students had to
> build design and build something that would protect an egg from breaking
> when thrown off a tall building. Guess what design won? The one that wrapped
> the egg in layers of Styrofoam that almost completely shattered when it hit
> the ground, BUT the egg didn't break! Go figure.

The calculation is simple: an egg presents the opposite problem from a
human head. In an egg contest, whether the yolk is damaged is
irrelevant, while the shell is the fragile item that breaks long
beforehand. In fact, "beforehand" is a misnomer, because no one checks
or cares to see whether the inside of the egg is scrambled afterward.
Success is only preserving the shell, which as it happens shatters long
before the inside gets scrambled. By contrast with the head, where the
inside gets scrambled long before the skull breaks, and this what
matters.

h