yeah… I don’t want to spark and heated debate… but I started looking into the differences between DOT and Snell, and pulled this up on the Snell website…but I think the key here is that BOTH tests use acceleration to gauge the performance of a helmet; which is much more accurate indication of how well a helmet protects then how thick/soft the material is.
Impact criteria tell the testers how to interpret test results. Ancient wisdom has it that it’s not the fall that does the damage, it’s the sudden stop. Both Snell and DOT measure the suddenness of the stop with an accelerometer, a device used to measure acceleration or in this case deceleration, that is mounted inside the headform. When the helmet smacks into the anvil, the accelerometer measures the headform deceleration throughout the duration of the impact event. This acceleration pulse is generally plotted as G’s versus milliseconds where one G is equal to the acceleration due to gravity on the surface of the earth. The testers analyze the acceleration pulse to determine whether the helmet passed or failed the test. Snell and DOT use different methods to analyze these pulses. Snell limits the peak value to 300 G’s. The DOT Standard requires that the peak acceleration not exceed 400 G’s but they also put duration limits on the acceleration pulse. The period of time for which the pulse exceeds 200 G’s must not be longer than 2 milliseconds. The period of time for which the pulse exceeds 150 G’s must not be longer than 4 milliseconds. Snell, among others, questions the validity of these duration criteria. […]
so it sounds like there are two main differences;
Snell has a max peak acceleration of 300- period, while DOT allows for peaks of 400, but no more than 150 for more than 4 ms. So to pass SNELL, you have to keep the acceleration inside the helmet lower over all, but the duration of acceleration technically could be more than what is certifiable under DOT.
BUT keep in mind, ALL Snell impact tests are performed at 110 joules; versus DOT impacts of 110 for only large helmet sizes.
Check out the table on the website for further examination.
I also thought this little bit was interesting. But then again… it is the SNELL website
There are also administrative differences between Snell and DOT.[…] Snell technicians in Snell labs tested samples of the helmet to Snell standards before the helmet was certified. Furthermore, as a condition of certification, Snell regularly buys samples of all Snell certified products and brings them into our lab for follow-up testing.
DOT certification is done on the honor system. The helmet’s manufacturer determines whether his helmets satisfy DOT and then claims the qualification for himself. There is not even a reporting requirement. […]