from the senior engineer of Bell Sports: *"Another source of field experience is our experience with damaged helmets returned to customer service... I collected damaged infant/toddler helmets for several months in 1995. Not only did I not see bottomed out helmets, I didn't see any helmet showing signs of crushing on the inside."
In 1987, the Australian Federal Office of Road Safety found that in real accidents *"very little crushing of the liner foam was usually evident... What in fact happens in a real crash impact is that the human head deforms elastically on impact. The standard impact attenuation test making use of a solid headform does not consider the effect of human head deformation with the result that all acceleration attenuation occurs in compression of the liner. Since the solid headform is more capable of crushing helmet padding, manufacturers have had to provide relatively stiff foam in the helmet so that it would pass the impact attenuation test..."*
from the senior engineer of Bell Sports: *"Another source of field experience is our experience with damaged helmets returned to customer service... I collected damaged infant/toddler helmets for several months in 1995. Not only did I not see bottomed out helmets, I didn't see any helmet showing signs of crushing on the inside."
In 1987, the Australian Federal Office of Road Safety found that in real accidents *"very little crushing of the liner foam was usually evident... What in fact happens in a real crash impact is that the human head deforms elastically on impact. The standard impact attenuation test making use of a solid headform does not consider the effect of human head deformation with the result that all acceleration attenuation occurs in compression of the liner. Since the solid headform is more capable of crushing helmet padding, manufacturers have had to provide relatively stiff foam in the helmet so that it would pass the impact attenuation test..."*
Guy
to be honest softer or harder foam, a helmet has what a inch? to try to cause a significant slowing of the heads deacceleration, thats hard job if not impossible.
probably how ever it's built would help from sliding as would cloth caps etc.
from the senior engineer of Bell Sports: *"Another source of field experience is our experience with damaged helmets returned to customer service... I collected damaged infant/toddler helmets for several months in 1995. Not only did I not see bottomed out helmets, I didn't see any helmet showing signs of crushing on the inside."
In 1987, the Australian Federal Office of Road Safety found that in real accidents *"very little crushing of the liner foam was usually evident... What in fact happens in a real crash impact is that the human head deforms elastically on impact. The standard impact attenuation test making use of a solid headform does not consider the effect of human head deformation with the result that all acceleration attenuation occurs in compression of the liner. Since the solid headform is more capable of crushing helmet padding, manufacturers have had to provide relatively stiff foam in the helmet so that it would pass the impact attenuation test..."*
Guy
Guy, just for the record, could you post cites? Might want to refer to these myself, and chapter and verse are the best defence to mull-headed think-of-the-children arguments...
On Mon, 21 Apr 2008 22:27:24 GMT, _ <[email hidden]> said in <[email hidden]>:
Quoted message said:
Guy, just for the record, could you post cites? Might want to refer to these myself, and chapter and verse are the best defence to mull-headed think-of-the-children arguments...
I'll ask Richard Keatinge, I think this came from him.
Guy, just for the record, could you post cites? Might want to refer to these myself, and chapter and verse are the best defence to mull-headed think-of-the-children arguments...
Jim Sundahl's Letter to CPSC on its Bicycle Helmet Standard <www.cpsc.gov/LIBRARY/FOIA/foia98/pubcom/34c7a89b.pdf>
The letter is from 1998 and the author is/was a senior engineer for Bell Sports. Another interesting snippet is:
"Now I want to offer some common sense and basic physics. First, energy management is often discussed regarding helmet standards. This is a false concept. No helmet standard in the world even measures energy management or absorption nor have a pass/fail criteria for energy management. A helmet can absorb zero energy and still pass any helmet standard in the world. Energy absorption is a function of input velocity minus rebound velocity. No standard requires a laboratory to even measure rebound velocity never mind dictating that the coefficient of restitution be less than 0.5 or something. A helmet can rebound with the full input velocity and pass quite well. Moreover, it can be imagined that any number of liner materials could absorb energy better than contemporary helmet liners but in fact produce a very poor helmet. A couple of good energy managers are soft lead sheet and modeling clay. Impacting either of these produces negligible rebound velocity. In other words, they absorb virtually all of the impact energy. None of us are advocating these materials for helmet liners because energy absorption is not very important for helmets. I think that any discussion of helmet test criteria that includes the word "energy" is suspect and might be misleading."
