Helmets on GMTV

[Just Zis Guy]

On Sun, 11 Jan 2004 13:14:35 GMT, [email protected] (Patrick Herring)
wrote:

>I was after a first approximation as to what helmets can possibly do.

They can prevent cuts and abrasions. As far as I can tell the upteen percent of injuries which
helmets prveent are essentially the trivial ones.

Mark's quoted source gives a very fair indication of why lids can't prevent the injuries which
cauise death and permanent intellectual disablement.

The number one fallacy in helmet promotion is to take the figure for injuries prevented and apply it
to the number of deaths and disabling injuries, claiming that, say, two thirds of lives or two
thirds of disabling injuries would be saved. Curnow clearly shows this up as Complete Bollocks [tm].

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

 

[James Annan]

Patrick Herring wrote:

> I'm still wondering how it could be shown that the polystyrene could reduce the 300g to 100g.

I think you want v^2 = 2as

where v is the impact velocity, a is the acceleration and s is the distance (ie the amount the
helmet can crush). Stick in a few numbers, making sure you use the same units!

I think there is little doubt that a helmet can help in some circumstances. But it's a long reach to
get from there to "you must be an idiot to not wear one, is your head not worth that much?", and a
vast leap further still to think that helmet compusion is remotely justifiable.

James

 

[Tony Raven]

Just zis Guy, you know? wrote:
>
> They can prevent cuts and abrasions. As far as I can tell the upteen percent of injuries which
> helmets prveent are essentially the trivial ones.
>

There are lots of things they can't do. What they can do is, as you say, reduce cuts and abrasions
but they can reduce blunt trauma to the skull and they can ameliorate deceleration through collapse
of the foam structure on impact. The role of what they can do for brain injury though is complex and
one in which simple linear deceleration plays a relatively minor.

Tony

 

[Mark Thompson]

> one in which simple linear deceleration plays a relatively minor.

Can't work out whether this is lack of proof reading or deliberate. Either way I fell off my chair.

 

[Tony Raven]

Mark Thompson wrote:
>
> Can't work out whether this is lack of proof reading or deliberate.

Sods law on the send button.

> Either way I fell off my chair.

Hope you were wearing a helmet at the time ;-)

Tony

 

[Pmailkeey]

On Wed, 07 Jan 2004 08:54:50 +0000, "[Not Responding]"
<[email protected]> wrote:

Dodgy stats [90 brain damaged children every week - surely not true] )and dodgy common sense. )

They should be more careful in the maternity ward.

I am particularly livid on this topic because so many people have told )me off since my crash for
:[a] not choosing transport with 'more metal )around me' and not wearing a helmet. The two are
:related in that )the real issue is that people shouldn't need armour of any sort.

Was your head injured in your accident ?

Mine might have been, but the medics were more concerned with the smashed chest and missing
bit of leg.
--
Comm again, Mike.

 

[Nick Kew]

In article <[email protected]>, one of infinite monkeys
at the keyboard of "[Not Responding]" <[email protected]> wrote:
> unconcious - yes. Real damage - none detectable! The head bash worried other people but was the
> least of my worries.

Solid evidence there. If you'd been encumbered with a helmet, you'd have a broken neck out of it.

... Well, makes as much sense as "helmet saved life" stories.

> Same here; shoulder/arm took the damage and pedal took flesh off shin.

Ouch:-(

--
Hutton: Nobody is asking why Blair was so keen to have a damaging inquiry into a minor side-issue of
going to war.

So, what has he successfully deflected media attention from?

 

[Pmailkeey]

On Wed, 07 Jan 2004 09:00:00 +0000, "[Not Responding]"
<[email protected]> wrote:

A link for the gmtv view on the issue : ) )http://www.gmtv.co.uk/index.cfm?articleid=9418 ) )I
:would phone and write and try and get a slot but can't as i'm [a] )off sick and on pretty good
ainkillers that seem to have sot any )ability to write clearly. ) )Hope someone else does/

via [email protected]

The article doesn't say much - possibly as usual - like what's causing the accidents. School trips
are looking likely the "time" - but for what reason ?
--
Comm again, Mike.

 

[-Lsqnot Respond]

On Mon, 12 Jan 2004 13:09:51 GMT, [email protected]
(pmailkeey) wrote:

>On Wed, 07 Jan 2004 08:54:50 +0000, "[Not Responding]" <[email protected]> wrote:
>
>Dodgy stats [90 brain damaged children every week - surely not true] )and dodgy common sense. )
>
>They should be more careful in the maternity ward.
>
>I am particularly livid on this topic because so many people have told )me off since my crash for
>:[a] not choosing transport with 'more metal )around me' and not wearing a helmet. The two are
>:related in that )the real issue is that people shouldn't need armour of any sort.
>
>
>Was your head injured in your accident ?

That depends on how you define injured. Blood - yes. 30 minutes unconcious - yes. Real damage - none
detectable! The head bash worried other people but was the least of my worries.

>Mine might have been, but the medics were more concerned with the smashed chest and missing
>bit of leg.

Same here; shoulder/arm took the damage and pedal took flesh off shin.

 

[RogerDodger]

Patrick Herring wrote:

> On another tack: does anyone know what deceleration rate causes brain damage...and how it relates to the maximum impact speed for cycle helmets?

A Google search using "head Injury criterion" and "Wayne State"
returns an excellent chapter titled "Biomechanics of Closed Head Injury"...

[PDF] P ch 02.025
File Format: PDF/Adobe Acrobat - View as HTML
... This work, and the Head Injury Criterion, are discussed at greater length in section
2.5.1. Further investigations at Wayne State University through the 1960s ...
www.edc.gsph.pitt.edu/neurotrauma/thebook/Chap02.pdf

Basically the level of the acceleration and the duration of the impact are what's important when considering linear (not angular/rotational) accelerations. Consider an impact of an object dropped from a height of 1.5 metres - the velocity at impact is the sqRoot(2*gravity*1.5metres) = around 5.5 m/s. The deceleration at impact is determined by the velocity and the duration of the impact = dV/dt. If the duration of the impact is 1 millisecond then the deceleration is 5.5/0.001 = 5,500m/s/s which is approx 550g's (where g is the acceleration due to gravity = 9.8 metres per second per second)

The time taken to crush a 2.5 cm thick helmet under a constant velocity of 5.5m/s is approx 5 milliseconds, and it's this stretching of the impact duration that is critical in reducing the peak acceleration.

Helmet standards usually require a 5kg headform to be dropped from a height of around 1.5 metres and the standard requires that the headform acceleration shall not exceed a peak of 400 g, 200 g for a cumulative duration of three milliseconds and 150 g for a cumulative duration of six milliseconds.

Roger

 

[Chris Malcolm]

"Tony Raven" <[email protected]> writes:

>Just zis Guy, you know? wrote:

>> They can prevent cuts and abrasions. As far as I can tell the upteen percent of injuries which
>> helmets prveent are essentially the trivial ones.

>There are lots of things they can't do. What they can do is, as you say, reduce cuts and abrasions
>but they can reduce blunt trauma to the skull and they can ameliorate deceleration through collapse
>of the foam structure on impact. The role of what they can do for brain injury though is complex
>and one in which simple linear deceleration plays a relatively minor.

Note also that human reaction times are such that at speeds < approx 15mph most people in most
accidents have time to throw their arms out, and in general take action to minimise head injury,
whereas above that speed things happen too fast. So helmets protect you against injury at the kind
of closing speeds where folk do well at protecting themselves (ordinary running speeds), and don't
protect you past that speed threshold where accidents suddenly become much more risky to the head.

In short, helmets (as they're currently made) are about as much good as an oven glove that protects
you against burning yourself holding a hot cup of tea, which you have enough time to let go of
anyway before you get burnt, but not against boiling water or oven-hot metal.

--
Chris Malcolm [email protected] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]

 

[Mark Thompson]

> Note also that human reaction times are such that at speeds < approx 15mph most people in most
> accidents have time to throw their arms out, and in general take action to minimise head injury,
> whereas above that speed things happen too fast. So helmets protect you against injury at the kind
> of closing speeds where folk do well at protecting themselves (ordinary running speeds), and don't
> protect you past that speed threshold where accidents suddenly become much more risky to the head.
>
> In short, helmets (as they're currently made) are about as much good as an oven glove that
> protects you against burning yourself holding a hot cup of tea, which you have enough time to let
> go of anyway before you get burnt, but not against boiling water or oven-hot metal.

You might have the reactions of a ninja praying mantis on speed but not everyone is so blessed. I
know I'm quite capable at hitting the ground without reacting in the slightest. Fortunately the only
time it happened my head broke the fall.

 

[Ambrose Nankive]

In news:[email protected],
Mark Thompson <[email protected] (change warm for hot)>
typed:
>> Note also that human reaction times are such that at speeds < approx 15mph most people in most
>> accidents have time to throw their arms out, and in general take action to minimise head injury,
>> whereas above that speed things happen too fast. So helmets protect you against injury at the
>> kind of closing speeds where folk do well at protecting themselves (ordinary running speeds), and
>> don't protect you past that speed threshold where accidents suddenly become much more risky to
>> the head.
>>
>> In short, helmets (as they're currently made) are about as much good as an oven glove that
>> protects you against burning yourself holding a hot cup of tea, which you have enough time to let
>> go of anyway before you get burnt, but not against boiling water or oven-hot metal.
>
> You might have the reactions of a ninja praying mantis on speed but not everyone is so blessed. I
> know I'm quite capable at hitting the ground without reacting in the slightest. Fortunately the
> only time it happened my head broke the fall.

He doesn't strike me as the ninja praying mantis type. I think to some extent this kind of thing can
be made instinctual.

A

 

[Patrick Herring]

RogerDodger <[email protected]> wrote:

| Patrick Herring wrote:
|
| > On another tack: does anyone know what deceleration rate causes brain damage...and how it
| > relates to the maximum impact speed for cycle helmets?
|
| A Google search using "head Injury criterion" and "Wayne State" returns an excellent chapter
| titled "Biomechanics of Closed Head Injury"...
|
| [PDF] P ch 02.025 File Format: PDF/Adobe Acrobat - View as HTML ... This work, and the Head Injury
| Criterion, are discussed at greater length in section
| 2.5.1. Further investigations at Wayne State University through the 1960s ...
| www.edc.gsph.pitt.edu/neurotrauma/thebook/Chap02.pdf

Interesting, thanks.

--
Patrick Herring, Sheffield, UK http://www.anweald.co.uk

Eala Earendel engla beorhtast ofer middangeard monnum sended.

 

[Patrick Herring]

James Annan <[email protected]> wrote:

| Patrick Herring wrote:
|
| > I'm still wondering how it could be shown that the polystyrene could reduce the 300g to 100g.
|
| I think you want v^2 = 2as
|
| where v is the impact velocity, a is the acceleration and s is the distance (ie the amount the
| helmet can crush). Stick in a few numbers, making sure you use the same units!

Aha, that other formula that doesn't have t in it (my applied maths days are long ago), thanks.

So, if the 3cm of polystyrene is squashed, miraculously, to 0 and we start at the speed for the
300g limit, v=12.5mph=5.6m/s, s=0.03m, so a=522.7m/s^2=53g. Suppose, more realistically, the poly
is squashed to about a third, a=80g. Suppose it's just a half, a=106.7g. Anyone got an old helmet
and a mallet?

So it looks like the helmet design conforms to the minimum you need to get below 100g and therefore
avoid brain damage, assuming everything else about your collision is textbook.

| I think there is little doubt that a helmet can help in some circumstances. But it's a long reach
| to get from there to "you must be an idiot to not wear one, is your head not worth that much?",
| and a vast leap further still to think that helmet compusion is remotely justifiable.

Sure, preaching to the converted .

--
Patrick Herring, Sheffield, UK http://www.anweald.co.uk

Eala Earendel engla beorhtast ofer middangeard monnum sended.

 

[Sandy Morton]

In article <[email protected]>, Patrick
Herring <[email protected]> wrote:
> Aha, that other formula that doesn't have t in it (my applied maths days are long ago), thanks.

> So, if the 3cm of polystyrene is squashed, miraculously, to 0 and we start at the speed for the
> 300g limit, v=12.5mph=5.6m/s, s=0.03m, so a=522.7m/s^2=53g. Suppose, more realistically, the poly
> is squashed to about a third, a=80g. Suppose it's just a half, a=106.7g. Anyone got an old helmet
> and a mallet?

> So it looks like the helmet design conforms to the minimum you need to get below 100g and
> therefore avoid brain damage, assuming everything else about your collision is textbook.

Your figures look very convincing and your explanation is brilliant - am I still alive and assuming
I had half a brain at the beginning do I now have more or less?

--
A T (Sandy) Morton on the Bicycle Island In the Global Village http://www.sandymillport.fsnet.co.uk

 

[Pmailkeey]

On Mon, 12 Jan 2004 15:02:53 +0000, [email protected] (Nick
Kew) wrote:

In article <[email protected]>, one of infinite monkeys ) at the keyboard
f "[Not Responding]" <[email protected]> wrote: )> unconcious - yes. Real damage -
:none detectable! The head bash worried )> other people but was the least of my worries. ) )Solid
:evidence there. If you'd been encumbered with a helmet, you'd have )a broken neck out of it. ) )...
:Well, makes as much sense as "helmet saved life" stories. ) )> Same here; shoulder/arm took the
:damage and pedal took flesh off shin. ) )Ouch:-(

In my case, my knee broke the truck's headlight whose broken glass gouged a lump out me leg.
--
Comm again, Mike.

 

[Patrick Herring]

Sandy Morton <[email protected]> wrote:

| In article <[email protected]>, Patrick Herring <[email protected]> wrote:
| > Aha, that other formula that doesn't have t in it (my applied maths days are long ago), thanks.
|
| > So, if the 3cm of polystyrene is squashed, miraculously, to 0 and we start at the speed for the
| > 300g limit, v=12.5mph=5.6m/s, s=0.03m, so a=522.7m/s^2=53g. Suppose, more realistically, the
| > poly is squashed to about a third, a=80g. Suppose it's just a half, a=106.7g. Anyone got an old
| > helmet and a mallet?
|
| > So it looks like the helmet design conforms to the minimum you need to get below 100g and
| > therefore avoid brain damage, assuming everything else about your collision is textbook.
|
| Your figures look very convincing and your explanation is brilliant - am I still alive and
| assuming I had half a brain at the beginning do I now have more or less?

Does it hurt? <g>

--
Patrick Herring, Sheffield, UK http://www.anweald.co.uk

Eala Earendel engla beorhtast ofer middangeard monnum sended.