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Past Issues Index
Roadfly Magazine
Chef Alton Brown: BMWs, Books, Good Eats & Iron Chef America
Issue Fourteen
November 8, 2004
Alton Brown:
Talks Bikes, Books, & Good Eats
Helmet Guide:
What to Look For
2004 BMW X3 2.5i Sport
2005 Chrysler 300C Hemi
iPod FM Transmitter Review
Coming Next Issue
Chip Foose
BMW 760Li
VW Phaeton W12
Prepare for Winter

How To Choose A Helmet:
Head Games (continued)

Snell Retention Test

Snell Impact Testing

Snell Penetration Testing

Official Web sites:
Snell Web Site
Arai Americas
Bell Racing
Snell uses the next three helmets in tests for impact resistance, positional stability, dynamic retention, shell penetration, and if applicable, flame resistance testing, chin bar testing and face shield penetration.

Impact resistance testing involves a guided fall on to various test anvils, while a head form (fitted with various accelerometers) reports the peak G force during impact. Snell expects the load to remain under a 300 G limit - if 300 G's are exceeded, the helmet is rejected. For comparison, the DOT suggests that the number of G's not exceed 400.

Positional stability and dynamic retention testing is a fancy way of saying, "The helmet has to stay on during an impact." These tests make sure the helmet can't roll off during a crash, and also test the chin strap to make sure that it doesn't break or loosen during an impact. Again, Snell uses test equipment designed specifically to measure performance, per their specifications.

Shell penetration testing involves dropping a weighted, pointed striker in a guided fall onto the helmet from a prescribed height. If the striker penetrates the helmet, the helmet is rejected. Face shield penetration testing involves an air rifle and a soft lead pellet. Snell fires three shots at the face shield and inspects for signs of penetration.

Chin bar testing only applies to full-faced helmets, and involves dropping a 5kg weight onto the chin bar from a prescribed height. Snell observes the amount of deflection and inspects for signs of breakage or excessive deflection.

Flame resistance testing involves a 790-degree centigrade flame. The helmet is subjected to the flame and is then expected to self extinguish within a specified amount of time after the flame is removed. Snell expects that the interior of the helmet must not exceed 70 degrees centigrade at any time during the test.

The tests, despite having their descriptions simplified for the sake of this article are complex and thorough, and easily exceed DOT specifications. Snell standards are typically updated every five years, with the newest set of standards expected to arrive some time in 2005. Helmets that meet the Snell standards are identified by either an adhesive sticker (usually placed inside the helmet) or by a cloth tag that's sewn to the chin strap. Manufacturers pay Snell about $1 per sticker, in addtition to the initial testing fee.

Finally, any helmet that's been involved in an impact should be returned for inspection by the manufacturer, as even the most thorough self-inspection can't detect signs of damage. Snell further recommends that all helmets be replaced after five years.

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