Date: September 10, 1997 To: All Snell Certified Manufacturers From: Edward B. Becker,Executive Director
This is the seventeenth of the Foundation's quarterly newsletters to the
helmet manufacturing industry. The sixteenth was sent out last June.
Comments and items for inclusion in subsequent issues are invited.
Anaheim Manufacturers' Meeting
The manufacturers' meeting took place Wednesday, September 3, 1997 in
Anaheim, California, just prior to the Interbike Show. Dr. Fenner, Gib
Brown, Steve Johnson, Frank Lin and Ed Becker represented the
Dr. Fenner, the Foundation's president, opened the meeting and welcomed
the attendees. Frank Lin then discussed the Foundation's internet site.
Frank's presentation is summarized further on but there are two points
worth repeating: links to certified manufacturers and the Snell
certified products lists. All certified manufacturers should check the
lists to ensure that their certified products are present and are
correctly listed. Then, if you have your own web site, please allow us
to set up a link. Many of the visitors to the Snell site browse through
the certified helmets and then access the manufacturers for more
information. We believe in these Snell certified helmets and want to
see them on peoples' heads. We hope that the Snell web site will help
make this happen.
Ed Becker presented a comparison of twin-wire versus monorail impact
testing. This comparison drew on data collected for the Consumer
Product Safety Commission's study. Snell collected data on both kinds
of impact device but using the same instrumentation. As a result, we
were able to study the mechanical artifacts introduced by the mechanical
systems without any instrumentation bias.
Although this study is not yet completed, there is no indication that
either system is inappropriate for helmet testing. A brief summary of
the presentation is included further on.
Over the last year, the study of bicycle injury performed by the Harborview Medical Center Injury Prevention and Research Center has culminated in several papers published in scientific and medical journals:
Thompson DC, Rivara FP, Thompson RS. Effectiveness of bicycle safety helmets in preventing head injury: A case control study. JAMA 1996; 276:24:1968-73.
Thompson DC, Nunn ME, Thompson RS, Rivara FP. Effectiveness of bicycle helmets in preventing serious facial injury. JAMA 1996; 276:24:1974-75.
Thompson DC, Rebolledo V, Thompson RS, Kaufman A, Rivara FP. Bike speed measurements in a recreational population: Validity of self reported speed. Injury Prevention 1997; 3:43-45.
Thompson DC, Thompson RS, Kaufman A, Rivara FP. Increasing bicycle helmet effectiveness: The importance of proper fit and wearing position. HMO Practice 1997; 11(1):25-26.
Rivara FP, Thompson DC, Thompson RS, Rebolledo V. The epidemiology of bicycle injuries and risk factors for serious injury. Injury Prevention 1997; 3:110-114.
Rivara FP, Thompson DC, Thompson RS, Rebolledo V. Injuries involving off road cycling. Journal of Family Practice 1997; 44(5) 481-485.
Ching RP, Thompson DC, Thompson RS, Thomas DJ, Chilcott WC,
Rivara FP. Damage to bicycle helmets involved with
crashes. Accident Analysis & Prevention (in press
The Foundation published an overview in September, 1996, which provides
a clear, concise summary of the study and its importanfindings.
Circumstances and Severity of Bicycle Injuries by Rivara FP, Thompson DC
and Thompson RS has been posted on Snell internet web site.
Snell Web Site
The Snell Foundation World Wide Web Site, http://www.smf.org, now
includes more than thirty pages of helmet and head protection
information. There are descriptions of the Foundation and its
certification programs, lists of certified products, links to ftp
downloads of Snell Standards and drafts and links to other web sites of
Dr. Frank Lin maintains the site and makes bi-weekly additions and
updates to the materials. Frank has received many compliments for his
clear, entertaining and user-friendly presentation of this useful
information. In the last six months, Sympatico, one of Canada's largest
internet providers, gave the Snell pages a Four Star rating in a survey
of health related web sites.
One of the primary purposes of the site is to acquaint the public with
the importance of selecting and wearing the most effective protective
headgear. Once the Foundation tests and certifies a helmet, we want
people to wear it. If you manufacture or sell Snell certified helmets
and you maintain an internet web site, please contact Dr. Lin to see
about establishing a link.
Frank welcomes comments and suggestions regarding any aspect of the web
Impact Device Comparison
Last December the Foundation cooperated in a Consumer Product Safety
Commission study of twin-wire and monorail impact test devices. Since
the Foundation has both types of device, our participation afforded an
opportunity to perform our own comparison. Our comparison is
necessarily much narrower than the CPSC study which includes data from
many test organizations involving many different hardware
However, our study may be deeper. The CPSC study compares peak
acceleration only. Our comparison considers the entire impact
acceleration time history and will attempt to identify mechanical
artifacts associated with each device type.
Although the study is not yet complete, there are a number of
observations worth describing. Both Snell systems are remarkably
repeatable. In impacts between a falling sphere and the CPSC's MEP pad,
we were impressed at how successive impacts overlay each other. Not
just during the period of actual impact but even well after the sphere
had rebounded from the pad.
We also noted system resonances in the twin-wire device. The
interaction between the sphere and the MEP contains excited a 200 Hertz
vibration in the twin wire hardware which persisted long after the
sphere had rebounded from the pad. A deconvolution analysis suggests
that this resonance did not affect the peak acceleration measurement and
that the resonance effect would be negligible in a helmet test. The MEP
pad is much stiffer than current helmet configurations so that helmet
impacts could not excite the 200 Hertz vibration to any significant
Finally, there appeared to be a strong rotational effect in the monorail
impacts. Essentially, an offset in the system center of gravity forced
by the monorail system hardware causes the system to rotate in response
to impact. The rotation produces a higher measured acceleration during
the test. Although the monorail permits only a tiny amount of rotation,
about 20 minutes of arc or one third of a degree, the time domain is
down in the milliseconds. Comparison of the acceleration traces seems
to support conclusions that the initial monorail accelerations are about
10% greater than the twin-wire measurements because of these rotational
effects. Furthermore, the acceleration traces suggested interference in
the monorail bearing systems during the impact event.
If the conclusions are correct, bearing forces must certainly exceed
1000 lbs and could go considerably higher. Since most of the commonly
used bearing sets are rated for 250 lbs or less, it is no surprise that
many have found that bearings must be replaced regularly.
Mr. Serge Dextraze of Cadex reports that there are bearings available
that are rated for 1000 lbs but also that some investigators have
measured bearing forces in excess of 5000 lbs.
It is important to state that there are no indications that either
system is inappropriate for helmet testing. The differences observed in
peak acceleration are on the order of the calibration error of the
accelerometers. Selection of impact test gear should continue to be
based on local needs and conditions.
HPE Opens in England
Brian and Paul Walker have established HPE, a private, for-profit,
helmet testing company at the former Snell UK site:
Unit 4 Farnham Business Centre
Farnham, Surrey GU9 7UP
We wish Brian, Paul and HPE all good fortune. I hope that they will
continue to be able to provide advice and guidance to me and my
colleagues in the US, and technical testing services to the European
community and beyond.
ISO Guide 25 Accreditation for Snell, CA
As of June 2, 1997, the Snell Memorial Foundation's California
laboratory has been awarded American Association for Laboratory
Accreditation (A2LA) approval for helmet testing. A2LA is an
internationally recognized authority administering quality laboratory
accreditation programs to ISO/IEC Guide 25 "General Requirements for the
Competence of Calibration and Testing Laboratories." The scope of the
A2LA accreditation includes all of the tests covered in the Foundation's
bicycle, motorcycle, auto racing, non-motorized sports and harness
racing helmet standards. The accreditation confirms that the
Foundation's California laboratory has the capability to perform Snell
testing and has the quality control necessary to assure the accuracy and
validity of Snell test results.
The Foundation sought this accreditation as part of its continuing commitment to quality. Since its beginning in 1957, the Foundation has urged manufacturers to design and build quality protective helmets and has urged the public to seek out and wear them. As a recognized authority in helmet safety, it is proper that the Foundation submit itself to another recognized authority to demonstrate the quality of its own testing programs and procedures.
The Foundation looks forward to continuing in the A2LA program in order
to increase the recognition and value of Snell Certification Programs
for both helmet manufacturers and the helmet wearing public.
Consumer Reports Bicycle Helmet Evaluations
The June issue of Consumer Reports included an article on bicycle
helmets. The article warned consumers about a widely used plastic
buckle component and also awarded a surprisingly low impact protection
rating to one helmet currently certified to the Foundation's B-90
We reviewed our test records and conducted additional testing
immediately. We have concluded that the buckles and the helmet all
perform to the Snell requirements and that Snell Certified helmets
continue to provide premium levels of head protection. We remain
convinced of the accuracy of Snell testing and of the protective
capabilities of the fine bicycle helmets we certify.
Anyone who has read the Consumer Reports article and who has concerns
over the buckle or the capabilities of any Snell Certified helmet is
invited to call our special toll free number, 1-888-763-5599
(1-888-SNELL99). This line comes directly into our offices, I or one of
my colleagues will do our best to explain the tests and their
Snell Safety Education Center (SSEC)
As of December, 1996, the Snell Safety Education Center, a California
non-profit corporation, has taken up the Snell Memorial Foundation's
effort to promote the widespread use of protective headgear. The Center
is dedicated to all the ideals of the Foundation: to engage in
scientific, educational and charitable activities; to research and
develop safety equipment for the prevention of injuries; and to develop
and provide information, materials and services to encourage the use of
safety equipment. However, the Center is a distinct and autonomous
organization. Since there is no connection to the Foundation's testing
and certification programs, the Center will be able to work more
directly with consumer groups, helmet manufacturers and other charitable
Ms. Hong Zhang, who organized and directed the Foundation's current
helmet education programs, will continue these efforts as president of
the Snell Safety Education Center. As with the Foundation, Ms. Zhang
expects to work closely with state and community groups dedicated to
public safety. Working through the Center, Ms. Zhang hopes to improve
and expand the support provided to these vital state and community
S-97 and L-97 Standards
The 1997 Standard for Protective Headgear Used in Skiing and Other
Winter Activities (S-97) and the 1997 Standard for Protective Headgear
for Use with Low Powered Vehicles, Mopeds and Motorized Bicycles
(L-97)are now in their final form. Copies of these two new Standards as
well as the Foundation's draft equestrian helmet standard are available
from the Foundation's North Highlands Office.
Manufacturers are invited to submit samples for evaluation with respect to S-97, L-97 or the equestrian draft standard. Please contact the North Highlands office for further information.
Helmet Testing: Gib Brown Certification Labels: Ms. Bonnie Adams Public Education: Ms. Hong Zhang Administrative: Steve Johnson Internet Web Site: Frank Lin All Other: Ed BeckerPhone: (916) 331-5073; Fax: (916) 331-0359; E-Mail: firstname.lastname@example.org