What kind of protection does a helmet provide?
Helmets are tested in the lab for straight line (linear) blows only. Test procedures set by standards bodies like Snell, ANSI, and CPSC require a helmet containing a 5kg (11lbs) rigid headform to be dropped onto a flat anvil from a height of 1.5 to 2.0 metres (5ft to 6ft 8in). If more than 300g’s is imparted to the headform the helmet cannot be certified. The outer shell of the 1980’s hard shell helmet is designed to spread the force of an impact over a greater area of the head. The micro-shell of modern helmets does not do this, deforming instead and allowing the liner to start compressing at the point of impact. Whether this is good or not is open to question. All shelled helmets reduce friction in a slide compared to no-shell helmets. The helmet’s liner is made of foam sufficiently stiff that the head inevitably will absorb some of the impact. The stiffer the liner, the more shock the head will absorb. Theoretically, the liner is supposed to limit the deceleration for a typical fall
Helmets are designed, and subsequently tested in the laboratory, for protection against straight line (linear) blows only. Test procedures set by standards bodies like Snell and ANSI require a cycle helmet containing a 5kg rigid headform (i.e. a dummy head) to be dropped onto a flat anvil from a height of 1.5 to 2.0 metres (5ft to 6ft 8in). If more than 300g’s is imparted to the headform the helmet cannot be certified.
Simon Brooke wrote: >> > I agree with you. I just can’t buy that. We can clearly see ways in > which a helmet must change the physics of the impact. They do not do > ‘bugger all’. >Consequently we have to conclude from the overall > statistics that they do at least as much actual harm as good. > The data do not support that conclusion at all. It is one postulated explanation but there are others for tye counter intuitive populatiolevel data.
