Helmets

Peter Amey <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

RogerDodger said:

Peter Amey said:

... I was
astonished just how tough my last PFDB was. I broke the strap which
was
not replaceable and that rendered it scrap. Before throwing it away I
set about it with a wooden mallet, a large rubber mallet and finally
(having failed to make any visible effect on it at all) with a 4lb
club
hammer. Even that took four lusty blows before I got the polystyrene
inner to separate from the skin. The experience makes me better
understand the cognitive dissonance people suffer from between the
"surely they must do some good" and the absence of any whole
population
evidence that they do. The issue of "why" helmets don't work is now
even more interesting to me.

It is an interesting subject to me as well - what further directions
and aspects fascinate you Peter?

I am interested in reconciling two observed phenomena:

1. My (unscientific) experiment involving a club hammer and a helmet
which impressed me with its strength and convinced me that if anyone is
going to hit me over the head wih a hammer then I would rather I was
wearing a helmet.

2. The absence of any detectable reduction in KSI rates in areas where
there has been a step change in helmet wearing patterns.

I think reconciling these would be a very valid use of research funding.

Possible explanations include:

1. Risk compensation. A real, well documented phenomenon but unclear
whether it is enough on its own.

2. Real accidents bear no resemblance to being hit over the head with a
hammer.

Right. Your experiment was as bad as, or worse than, industry
certification procedures which involve the dropping of a helmet
containing a solid magnesium head form from 1.5 to 2 metres on to a
steel anvil. It didn't, and the industry procedures don't, simulate a
typical fall from a bicycle or a typical blow to the head, therefore
no conclusions what happens to the head (made of skin, bone, tissue
and water) can be made.

..... <snip>

[email hidden] (Patrick Herring) wrote in message news:<[email hidden]>...

Quoted message said:

Peter Amey <[email hidden]> wrote:
...
| P.S. At the risk of prolonging this thread even further, I was
| astonished just how tough my last PFDB was. I broke the strap which was
| not replaceable and that rendered it scrap. Before throwing it away I
| set about it with a wooden mallet, a large rubber mallet and finally
| (having failed to make any visible effect on it at all) with a 4lb club
| hammer. Even that took four lusty blows before I got the polystyrene
| inner to separate from the skin. The experience makes me better
| understand the cognitive dissonance people suffer from between the
| "surely they must do some good" and the absence of any whole population
| evidence that they do. The issue of "why" helmets don't work is now
| even more interesting to me.

Is it possible the thing was flexing, since there was so solid object
inside it, and thereby absorbing more energy that it would normally?

Yes, Peter should try the experiment again with the helmet on his head.

--
Dave...

quote='PK'Peter Clinch said:

My helmet was shattered on the right side. Before I'd found
out more about brittle failure I thought it might have saved me
a fractured skull, if not my actual life.

Not trying to fan any flames (;-) , but... I follow all the arguments about
energy absorption and brittle fracture, but surely any head protection
helmet works in two ways: energy absorption and load spreading? The latter
operates beyond the point of brittle fracture?

pk[/QUOTE]

Yeah but using the words "energy absorption and load spreading" without any attempt at qualifying or quantifying the extent to which these things occur, and whether the measured amounts of aceleration attenuation, energy absorption and force distribution count as meaningful towards the goal of the supposed ideal - that is the question.

I think there is often, and generally widespread, the tendency to use the terms like "energy absorption and load spreading" mistakenly - as if these terms take on a life of their own in the unfettered imaginations of some.
I think every time these 'means of protection' are avered to (that is uncritically and without the necessary qualification) then this gives, to willing would-be-believers, the equivalent of a blank cheque. The talk of "energy absorption and load spreading" is more likely to issue from flights of fancy erroneous expectations borne of wishful thinking (and fertilised by BsHit) free from the down to earth reality that science can support.

PK you're clinging to a forlorn desire to claim some smidgin of protection when there's so little, what there is is so insubstantial as to warrant the conclusion that it's insignificant.

Roger

Dave Kahn said:

[email hidden] (Patrick Herring) wrote in message news:<[email hidden]>...

Quoted message said:

Peter Amey <[email hidden]> wrote:
...
| P.S. At the risk of prolonging this thread even further, I was
| astonished just how tough my last PFDB was. I broke the strap which was
| not replaceable and that rendered it scrap. Before throwing it away I
| set about it with a wooden mallet, a large rubber mallet and finally
| (having failed to make any visible effect on it at all) with a 4lb club
| hammer. Even that took four lusty blows before I got the polystyrene
| inner to separate from the skin. The experience makes me better
| understand the cognitive dissonance people suffer from between the
| "surely they must do some good" and the absence of any whole population
| evidence that they do. The issue of "why" helmets don't work is now
| even more interesting to me.

Is it possible the thing was flexing, since there was so solid object
inside it, and thereby absorbing more energy that it would normally?

Yes, Peter should try the experiment again with the helmet on his head.

OK, and you try it at the same time without one! Alternate blows. Bags
I have first hit.

Peter