On May 15, 9:57 am, Marc Brett <
[email protected]> wrote:
> For all you doubting-Thomases who think helmets don't work in real-world
> collisions with vehicles.
>
> Bike helmet crushed, but head finehttp://www.madison.com/tct/news/index.php?ntid=133934
>
> A white paneled delivery truck ran over a UW-Madison graduate student's
> head on Division Street Friday afternoon and, except for a concussion,
> he wasn't hurt.
Hmmm, Just goes to show that human skulls, like eggshells, can be
surprisingly strong. Can't say the same for the polystyrene hat he was
weaing though, it looks like it just fell to bits. This is not
surprising given all the holes in modern cycle helmets and the fact
that they are only designed to absorb around 100 Joules of energy in
an 'ideal world' crash situation. (And this is for 'Snell' certified
helmets, a standard which is so 'high' that almost no helmets
currently available meet it).
In a classic 'over the handlebars' crash where a 75 kg cyclist is
doing only 15.6 Mph (7 m/sec) when a car pulls out and is hit by the
cyclist who summersault forward and lands head first the kinetic
energy carried by the airborne cyclist will be 1837 Joules, almost 17
times the load imposed on the helmet when certified to Snell
standards. If the helmet is the first point of impact it will simply
bottom out (or, as often happens with a modern helmet, break up) and
even if the helmet were to absorb all the energy it was designed to
94% of the energy developed in the crash must be dissipated by other
means, which potentially includes dissipation via the riders skull,
brain and body. It is obvious that much larger forces than even these
may be generated should someone be struck by a large, unyielding motor
vehicle travelling at speed, and this is without considering other
such all important factors such as the creation of rotational forces
within the brain in a violent road crash which may kill even when '
direct impact' injuries such as skull fractures do not occur.
Do helmets genuinely 'save lives'? I have serious doubts myself...