Brian Robertson said:I have one experience under my belt that would almost certainly have
resulted in me suffering serious and possibly life threatening injury
had I not been wearing a helmet.
Lots of people say this... I was one of them too, thanks to an accident
where I was caught up in someone else's prang when a car spun out from a
collision and picked me up in its path as I waited stationary in a side
road. Don't remember anything about the accident, and had concussion
that put me off work fro a fortnight and a shattered helmet but not much
else wrong.
Pretty easy to conclude from that that I was much better off with the
lid... but is that a safe conclusion? I'll never know for sure, and I
certainly don't want a repeat to find out, but let's consider some
salient points:
- helmets shatter (like mine did) in a brittle failure mode that
actually absorbs very little energy (I don't know if it just shattered
or deformed first).
- helmets are built /down/ to a minimum standard, because overbuilding
makes them less comfortable. The current standard (EN1078 typically) is
lower than previous standards, and was created mainly by manufacturers
who found it hard to build a comfortable helmet to previous standards
for a reasonable cost.
- that EN1078 standard they are built down to, and thus won't exceed by
much, is for ~100 joules absorption, which is a lot less than a skull
can take. It's about what's needed to take a fall while stationary onto
hard ground with no other vehicle involved. While such falls /can/
kill, they only do if you're remarkably unlucky. Hit with substantially
more than that energy the helmet is far more likley to undergo brittle
failure, and do practically nothing.
- you'd be amazed at what people have survived without crash helmets.
Fact is the human skull is actually pretty good at protecting its owner
from serious injury. It gets out of its depth in many collisions with
vehicles as the energies are rather over anything natural selection
would commonly come up against, but you should realise that helmets are
designed for incidents with /no other vehicle involved/ (it's in the BSI
description IIRC)
- you can't assume any collison with a vehicle is actually a high energy
one, just because the vehicle has lots of energy. My own accident is
one I've had to recreate purely in theory as I can't recall it /at all/,
but ISTM it's most likely my head was rammed down hard onto the bonnet
of the car. A car bonnet is a large panel that actually deforms quite
easily, and though it might well hurt it's quite possible it will deform
readily and absorb a lot of the energy. So I can't say for sure I'd
have been much worse off without a helmet.
- helmets can make matters worse by adding leverage to twisting motions,
being that much bigger that they make the difference between being hit
and not, and at high speeds their weight will actually add more energy
to a collision than they're designed to absorb. All of these things
make it difficult to say with certainty that a lid must have made things
better in many anecdotal incidences.
Quoted message said:I have had another experience in which
I came scarily close to killing myself when I wasn't wearing a helmet
and I have no doubt that the risk would have been much reduced had I had
a lid on.
But see above, and see the fact that helmets do not have any track
record of reducing serious head injuries, and there are times and places
when they can make things worse.
Quoted message said:Personally, I prefer to wear a helmet. Personally, a lot of people
obviously prefer not to.
I used to prefer wearing one, and the reason why I wore one on pretty
much every bike trip I made for a decade was I thought it made me safer
and was a common-sense thing to do. Having done a lot of reading I no
longer think that, but I also see there was a clear double-standard in
my approach to risk. I had assumed cycling was /considerably/ more
dangerous than e.g. walking and driving, but it turns out not to be the
case, so if I don't need extra protection for them, then why for
cycling? In my case I had to admit that the answer was I was
rationalising my existing behaviour (as is a typical thing for folk to
do). Now, that's not a Big Problem in this case, but I do think it was
important that I had actually realised that. I decided to try without
and the first few trips without one for a decade I felt naked, but it
soon got back to being normal. Formal end of the process was a trip to
NL, seeing thousands and thousands of Amsterdammers cruising around
without them, though they're at /least/ as much risk of the sort of
accident helmets are designed for as anyone else.
Quoted message said:I hadn't taken into account the possibility
that people wearing a helmet might take more risks and it's an
interesting possibility. For my part, I do everything possible to
minimise my risks whatever I am wearing.
Nice theory, but highly unlikely to be true. Consider the relative
safety of different speeds downhill, for example. A low speed, checking
your descent with the brakes, will reduce your stopping distance and
give you more effective reaction time, so will up your safety, as will
your lower energy in the event of parting company with the bike. So do
you do that for any reason other than needing to slow down for sharp
bends or already visible obstacles? Doubt it!
Similarly, while most of us do superficial mechanical checks on a
periodic basis you can minimise risks even more by giving the bike a
fuller mechanical check before each journey. In practice practically
nobody does this, though it is something possible that will minimise
risk. Fact is that as long as risk is /acceptably/ low we don't
actually go quite as far to reduce it as we like to think we do. It's a
bit much of a faff, to put it simply, and just as we'd all be safer if
we never went down stairs at speed without holding the bannister at all
times, in practice we know how to do it well enough that we're happy
trotting down stairs without grabbing the hand rail. 350 people die in
the UK in a typical year from trips and falls, especially those on
stairs, yet we don't wear helmets for that.
Quoted message said:I don't see cycling in my life as some thrill chasing sport.
Do you see driving and coming down the stairs as thrill-chasing sport?
Plenty of folk get killed doing them.
Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/