"David Kerber" <ns_dkerber@ns_ids.net> wrote in message
news:[email protected]...
> In article <
[email protected]>,
> Kevan@mouse- potato.com says...
> > On Mon, 22 Mar 2004 08:14:54 -0700, Mark Hickey
> > <
[email protected]>
from
> > Habanero Cycles wrote:
> >
> > >It's obvious the helmet "absorbed" a lot of the impact,
> > >hence my assumption that it would have been worse
> > >without
> > >it.
> >
> > Well, it's not. You have no idea, in fact, how much
> > impact the helmet
"absorbed"
> > either total or as a percentage of total impact force.
>
> If the helmet has a huge dent (crevice) in it the shape of
> the edge of a truck mirror, but is still intact, you know
> it absorbed a lot of energy.
Since I can make the same sort of indentation with my thumb
and hardly any pressure at all I would probably take issue
with that statement.
I took apart a helmet and did a bunch of tests on the
material. Nothing that used any real measuring instruments
but enough that I could see what they
did.
My opinion?
A helmet is probably pretty good at spreading a blow out so
avoid point contacts. This is good.
A helmet is probably moderately good at absorbing a medium
strength direct impact. This is probably worthless because
this range is only a very small amount of the blows received
in all accidents. If you wear a helmet for this that's your
call because there IS the chance that you could get one of
these loadings.
The trouble is that most fatalities on bicycles and most
serious injuries are caused by collisions with automobiles
and the energies in such accidents are many times greater
than a helmet could possibly absorb.
And helmets only work if you have a direct blow. If you
have an angular blow it can cause rotational injuries and
these are far worse than injuried caused by straight-on
direct blows.
You also have to understand that helmets are faked from
the start.
For instance, the calculations in which it is determined how
much speed the helmet can withstand and maintain a
deceleration below 300 gees are calculated using ONLY the
weight of the average head. Most of us realize that there is
a body attached to the head and that when you fall very
often there is at least some of the weight of the body
behind the head.
For another thing, although helmets are ALL scaled for 300
gees maximum acceleration, most women's skulls can only
withstand less than 250 gees. And children far less, as low
as 180 gees. This makes the lining of a helmet essentially
concrete to a woman or child. This isn't necessarily bad
since children generally don't fall very far and so the
smooth rounded interior generally prevents injuries by
spreading the contact area.
Now here's the worst part - modern helmets with their
jillion vents use even harder material so that point
loadings are increased dramatically on a real head though
this isn't measured since the testing is done with a
magnesium head model. These helmets will pass the tests but
are only fractionally as effective as the older helmet. And
the harder material is far more prone to breaking and
fractionating into pieces in the open spaces of the vents
thereby reducing the effectiveness still further.
The sum of all this is that a helmet simply isn't capable
of "saving a life" though they are fine for what they are
really capable of - which is reducing the severity of
minor injuries.
I could actually go on for a long time and get pretty
technical but there's no sense in it. Helmets have their
place in racing, riding off-road and for anyone that
isn't going to take more chances BECAUSE they feel
protected by a helmet.
But these are hardly reasons for the sort of response that
comes from the helmeteers - "Where's your helmet?"
