Re: [ST] Helmet Life

["Dan Wetherington" <DEW@xxxxxxxxxxxxx>]

I understand why the manufacturer can make statements to that effect
(i.e. helmet should be replaced), but I find it hard to believe that the
styrofoam will compress when the helmet hits IF there is nothing in the
helmet.  Most of today's helmets are made of very stiff composites
(glass fiber, carbon fiber, etc.) but even the polycarbonate shells will
resist flexing under such small loads.  How much energy are we really
talking about here?  Take the average mass of a helmet (any guesses? 
2-3kgs maybe?) and a drop height of say 1 meter (average seat height?). 


I guess the Motorcyclist article got me thinking about all this.  They
mention that none of the helmets they tested came close to bottoming out
the EPA liner, even in the "huge" SNELL drop (150J drop).  Even in the
"two-hit" scenario, I can't see how an empty helmet drop would affect
the outcome.

Once again, this is my $0.02.  

Dan



>>> Chris@xxxxxxxxxxxxxxxxxx 11/10/2005 8:56 AM >>>
My understanding is that when it drops (on the polycarbonate shell)
the
internal styrofoam (what we call expanded polystyrene) gets compressed
and may not return to it's previous shape ie. it has passed its
elastic
limit which is deliberately low.  That area of the helmet is then of
reduced protection if it's needed for real.

If you know which part hit the ground when it fell, or if it fell on a
soft surface I would suspect that it is questionable wether it needs
replacing.  It's a parameter that you need to include in the Return On
Investment decision you make for you and your family.

5 years is what I was told for shelf-life by non-manufacturer related
parties.

Chris Harwood
00 RS; Caberg J1Plus, 3yrs old

>>> DEW@xxxxxxxxxxxxx 10/11/2005 14:01:00 >>>
>>> Neil.Lindsey@xxxxxxx 11/9/2005 11:21 PM >>>
(snip)
It's the crushing of the styrofoam on the inside that helps decelerate
your brain cells.

>>>>>>>>>>>>>>>>>>>>

Which brings up my question:  Why does it matter, then, if your helmet
falls off the bike?  It is always stressed that you shouldn't let your
helmet fall, or that a dropped helmet should be checked out before
being
used again.  If there's no noggin inside the helmet, the foam liner
won't compress, leaving the (possibly) only damage to be cosmetic... 
I'm not saying we should go around throwing or dropping our helmets,
but
I just don't see a reason to throw out your $200+ helmet just because
you dropped it.

Feel free to show me how I may be wrong!


www.packereng.com 


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