Back Protectors, Testing, and CE Standards

[license2ill]

So the improtant part is that the available protectors can absorb the necessary amount of energy to at least minimize injury to an acceptable level, or prefereably eliminate injury within the common levels of energy encountered in the average impact. I think this is why testing is so important. If a piece of gear is expected to be used for riding, then it must be capable of dealing with the forces involved, and up to the task of minimizing impact forces to acceptable levels--like the point at which ribs or spinal processes will break when considering a back protector.  

Where I get confused and frustrated is with the knowledge of the levels of energy that are normally encountered in a crash impacts. Do the CE standards utilize that kind of data or provide protection that will be necessary from impacts that can be typically expected? With an impact energy of 50J, what force is created at impact without the added distance created by the padding? Are these forces likely to be encountered in a motorcycle crash? Is there good data available for these assumptions or is additional research necessary to create an effective standard?

I can't find this info for the Snell testing either. Snell references the levels of g's that the brain can withstand, and approves helmets according to their performance at an impact energy of 150J translated into g-force(300J maximum), but is 150J of impact energy to be expected in a typical crash? Is that number low or high? I assume the mortality rates of helmet wearers will give us the answers, but from what I've read, that information is either not available or at least not current. What is Snell using to base the impact energy levels? Anybody know?

I'd like to put my faith into the standards or a manufacturer's promises and intentions. However, I am not comfortable paying for a product and placing my safety in it with my fingers crossed that it will perform not only to my expectations, but to a level that can truly make a difference in the outcome of a crash.

I wish we had more to go on, or at least a standard that we can comfortably know our money has made a true difference in our protective measures. I can't imagine buying a product that hasn't been approved, rated, or scientifically tested before it gets thrown on my back. Except for the fact that everybody riding a motorcycle has bought just about every piece of gear wihtout demanding more than an opinion or approval from someone with arbitrary carsh experience.

Snell and CE may be very appropriate to the current available technology and the crash forces involved, but  none of that information is readily available to someone that steps into a shop to buy protective clothing, whether its for racing or street use.

It just gets more frustrating for me, too much money and too many expectations for us to not be given better information and/or better products.

[tzracer]

Where I get confused and frustrated is with the knowledge of the levels of energy that are normally encountered in a crash impacts. Do the CE standards utilize that kind of data or provide protection that will be necessary from impacts that can be typically expected? With an impact energy of 50J, what force is created at impact without the added distance created by the padding? Are these forces likely to be encountered in a motorcycle crash? Is there good data available for these assumptions or is additional research necessary to create an effective standard?

I have a mass of about 77kg which would be about 750N, if I fall 1m, that would be 750J of energy (in a 1m fall, my impact speed would be about 14.5 ft/s = 9.9 mph). The force created while dissipating 50J depends upon the distance. If I stop in 1m, 50N; 1cm, 5000N; 1mm, 50,000N. From car crash testing, huge forces can be encountered. The human skull can sustain forces of more than a ton before cracking. But a short fall on a solid surface can create such forces.

To test, one would have to create a test dummy for testing something like spine protectors. Probably hasn't been done since no one has seen a need to.

Wayne State University in Detroit (?) did most of the background research for creating crash test dummies that respond like a human. I am sure they have numbers for most bones and major organs of the body. How to get them is another matter.

I can't find this info for the Snell testing either. Snell references the levels of g's that the brain can withstand, and approves helmets according to their performance at an impact energy of 150J translated into g-force(300J maximum), but is 150J of impact energy to be expected in a typical crash? Is that number low or high? I assume the mortality rates of helmet wearers will give us the answers, but from what I've read, that information is either not available or at least not current. What is Snell using to base the impact energy levels? Anybody know?

Most helmet testing is based upon the Wayne state tolerance curve (do a search for "wayne state tolerance curve" - you may find more data than you want). It is a curve of accelerations on the vertical axis and time on the horizontal (as I recall, haven't seen one in a while). The brain can survive huge accelerations (500 to 600 gs, 1g will get you to 60mph in 2.75s, 600 gs would get you to 60mph in 0.0046 seconds), but only for short periods of time (milliseconds), lower accelerations for longer times. It is this tolerance curve that the DOT standard and Snell standard use. They work backwards from the curve to arrive at the energy levels (for their headform weight and height it is dropped).

It has been a while since I have looked into this stuff. I may have some time this weekend to try to find some answers for you.

[Eric Kelcher]

Brian sorry to contradict you but the Snell foundation does not use time in their approval process for helmets. Only DOT does (well sort of no test is actually needed only manf word that it would pass if tested)  Here is an interesting article on differences of the two and why have both certifications I think is best. But come to think of it I don't think I have ever saw a SNell approved non DOT approved helmet but have seen DOT non Snell approved helmets.

[tzracer]

I know Snell does not use times. By specifying a max acceleration and the impact energy, there is a time involved, but not explicitly expressed. That is, a 150J (5kg headform dropped 3.06m - Snell ignores the mass of the helmet) impact with no more than 300g acceleration should not exceed the limits of the Wayne state tolerance curve (I haven't done the math to check). If it exceeds the limits, then permanant brain injury will occur. AFAIK the Wayne state curve is the only one of its kind for brain injury.

I have a couple minutes:

If the head form would stop at 300g for the entire stop (worst case - which doesn't happen) the time would be 2.63 milliseconds.

The WSTC gives a value of about 2ms for 300g acceleration.

A helmet that does not have a DOT sticker cannot be sold for street use.

[license2ill]

Thanks for the awesome explanations, Brian.

I'm still wondering about the absolute effectiveness of any of the available standards. I'd hope they are pushing the envelope of technology, but with all of the math involved for a layperson, I still feel left in the dark with my fingers-crossed that somebody is looking out for our needs.

I'd hope that somebody is always pushing for better standards no matter what, and more research into the forces at work, but I hear a lot more criticism of helmet laws and paranoia of mandatory-use than I do of riders interested in understanding the standards and furthering technology to our advantage.