Brian Mack
and I thought helmets were just fashion accessories, much like racing
numbers...
-----Original Message-----
From: Les Earnest [mailto:les@cs.stanford.edu]
Sent: Friday, May 04, 2007 3:00 PM
To: ncnca@ncnca.org
Cc: Farrell, Shawn
Subject: USA Cycling invites you to break your noggin
Last year, USA Cycling announced a helmet rule change, allowing
helmets meeting a European standard called CEN to be used -- see
http://www.usacycling.org/news/user/story.php?id=2109. The Chair and
Vice Chair of the Headgear Subcommittee (F08.53) of ASTM
International promptly contacted the USA Cycling staff to recommend
that they reconsider this change, pointing out that even though some
helmets meeting that standard also meet U.S. requirements, which are
set by the U.S. Consumer Products Safety Commission (CPSC), many such
helmets do not. The key issue is that the CEN testing procedures can
be fiddled so as to get helmets to pass that are actually unsafe.
Specifics on the inadequacy of the CEN standard in the opinion of
Dave Halstead, F08.53 Chair, are given at the end of this note.
Halstead invited USA Cycling staff members to come to his testing lab
to witness comparative tests of helmets meeting the CEN and the CPSC
standards. When I returned from a trip to Alaska last September I
joined the discussion and also urged that USA Cycling reconsider its
helmet rule change. I received friendly responses indicating a
willingness to reconsider but the invitation to witness comparative
texts was not accepted and nothing further happened.
Having tried and failed to get this matter resolved off-line, I am
now going public. Fortunately, Helmets meeting just the CEN standard
cannot legally be sold in the U.S. but you or your friends can get
them overseas and bring them back. Please do not succumb to the urge
to buy a sexy Euro helmet that might put you in a coma for awhile or
that might leave you with impaired speech for the rest of your life.
If you would like to know what happened the last time we had really
stupid helmet rules, go to the Cyclops USA web site at
http://www.stanford.edu/~learnest/cyclops/, scroll down to September
1989 and read "The brain bucket bash."
-Les Earnest, Speaking for myself and not for any of the
organizations with which I'm affiliated
-----------------------------------
As pointed out in September 2006 by Dave Halstead:
"The issue is that the helmeted head form is unrestrained, it is not
riding a rail. As such, by playing with the geometry of the
shell/helmet you can get the helmet to spin on impact. The spinning
action attenuates or more correctly redirects the energy from a
linear motion to a rotational motion. The linear only accelerometers
in the head form record the low g's and everyone is happy. Here then
is the problem , if you do not get the spin, then you get the high
linear g's. If you do get the spin, the linear g's are in fact low,
but the rotational forces are high. It is a stupid test
system. These helmets will result in increased injury."
Dave also remarked:
"I do think that the error is in an attempt to make a direct
comparison. If the CEN standard required a restrained, direct impact
then the difference is not that much, but it does not require a
restrained direct impact. We tested two CEN compliant models here
last week to the CPSC standard. This was a case of the manufacturer
stating `We will test to the CPSC just to be sure but as it passes
CEN we know they are fine, except maybe for the label'. The best
number we got was a 338 [g] and the worst a 420. This is not a
surprise to us and happens in almost every case of a CEN helmet
submitted to us for CPSC."