CityCyclingEdinburgh Forum » Debate!

THE Helmet Thread

(881 posts)
  • Started 11 years ago by Wilmington's Cow
  • Latest reply from chdot

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  1. rust
    Member

    Since a helmet has saved my head from serious injury multiple times in my life while cycling on roads

    Mkns, can I ask what evidence you have for this?

    Posted 11 years ago #
  2. Kenny
    Member

    My head, with helmet attached, hit the ground at force. If the helmet had not been there, my head would have hit the concrete directly at significant speed.

    Posted 11 years ago #
  3. rust
    Member

    a helmet has saved my head from serious injury

    My head, with helmet attached, hit the ground

    I'm worried this might come across as incendiary or aggressive, so please don't take it that way. I am just interest in whether we can better understand each others position.

    However, to my mind these are not the same statement. The later is a statement of fact, while the former is conjecture.

    Posted 11 years ago #
  4. rust
    Member

    (if it helps that post was written while wearing a helmet as I'm about to go out on my bike - on-road, not off-road.)

    Posted 11 years ago #
  5. Kenny
    Member

    It's ok, I'll not take it as incendiary or aggressive. Is your point merely that I cannot prove that I would have had a serious injury, since it didn't actually happen?

    Posted 11 years ago #
  6. allebong
    Member

    It is a matter of simple indisputable physics that a helmet will reduce the force and hence acceleration on the head during an impact.

    The above statement has at best marginal relevance to whether you should wear one while cycling or not. In fact, swap 'cycling' for 'walking down stairs, going on a stepladder, walking down the street, driving a car' or any of the innumerable events that might cause you to strike your head.

    Posted 11 years ago #
  7. wee folding bike
    Member

    allenong,

    No, it's not that simple. The plastic hat has mass. Increasing the mass of the head increases the kinetic energy. The kinetic energy increase with velocity, the absorption characteristics of the hat are fixed.

    They also increase the diameter of your head and may stop your skull deforming to dissipate the energy of an impact.

    Posted 11 years ago #
  8. Instography
    Member

    The problem with the whole discussion is that there are no indisputable facts, including that one that I just wrote. There are at best probabilities although the size of those probabilities is disputable and variable. The interesting aspects of it are the assessments of risk and the processes by which people make their decisions, which might inform how other people make their own decisions.

    Posted 11 years ago #
  9. Uberuce
    Member

    Try Cycles: I think it was someone on here who said a rain coat won't keep you dry if you fall into a canal but will help if it rains, and that was their theory with helmets.

    Yep, that was me. There's a scrapyard worth of irony in that since writing that I have fallen into the canal while wearing a raincoat, and really wish I had been wearing a helmet at the time.

    Not, I hasten to add, because I was bothered by the wee grazes I inflicted upon my brow(which would almost certainly have been prevented by a helmet) but because the straps on my lid would have clamped my fancy rimless titanium-legged glasses to my head so I probably wouldn't have lost them.

    I think of the bike components I could have bought for what I paid to replace them and weep.

    I've written more extensively about helmets here:

    http://uberuce.wordpress.com/2012/12/04/i-have-a-scar-that-makes-me-lie-to-children-on-a-regular-basis/

    Since writing it I've been wearing my helmet less and less.

    I also have found that my scar is a useful barometer of whether the person I'm talking to has a religious or an empirical position on helmet use.
    Religious No-Lid cite it as an example of why helmets are bad.
    Religous Yes-Lid cite it as an example of why helmets are good.
    Empiricals cite it as an example of one of those funny little outlier exceptions you often get, and therefore not a great basis to make general policy on.

    Posted 11 years ago #
  10. Two Tired
    Member

    The problem with the whole discussion is that there are no indisputable facts,

    I beg to disagree good sir :-) As I said in the last, locked topic. It is an indisputable fact that when hit directly on the head whilst wearing a helmet, the helmet will absorb some of the force. I said some not all, and make no assurances as to whether it will absorb enough force to protect your head entirely but it will absorb some force. Do we wish to discuss the use of helmets in any other 'extreme' sport??

    No, it's not that simple. The plastic hat has mass. Increasing the mass of the head increases the kinetic energy. The kinetic energy increase with velocity, the absorption characteristics of the hat are fixed.

    Not really sure where you are going with this. The speed your head+helmet is traveling will be the speed you are going (wearing a helmet will require a very VERY small amount more energy to travel at that speed due to the very VERY small increase in mass). We can all agree that a collision involves a rapid deceleration of our bodies. This deceleration is brought about by the absorption of the force of whatever hits us. Yes we 'contain' a tiny tiny bit more kinetic energy when we are moving wearing a helmet. But we also then require a very very little more force applied to us to bring us to a standstill. The mass of the helmet cancels out.

    I generally stick to the physics, and if you want to argue with that then head on down to Westminster Abbey and see if Newton will answer you.

    Posted 11 years ago #
  11. Kenny
    Member

    There are at best probabilities although the size of those probabilities is disputable and variable

    This is entirely true.

    The only other "evidence" I have that I would have had a serious head injury is the opinion of three doctors, ranging from SHO up to Consultant, at the RIE who could not believe that I did not have even the slightest concussion, considering the description of my accident, my various broken and dislocated parts in other areas of my body, and the GPS evidence of the speed I was going. They thought I should still have had concussion despite (not because of) wearing a helmet, and made it quite clear to me that I was a very lucky boy indeed to have had the helmet on, as otherwise, in their opinion, I would have been significantly more injured. This, they told me, based on (a) evidence of what had happened to me, added to (b) their experience of treating injured cyclists, from both sides of the "do I wear a helmet" fence.

    However, people are correct when they say there is no indisputable evidence. I'll carry on wearing my helmet though, and I'm 100% against compulsory helmet wearing.

    Posted 11 years ago #
  12. Two Tired
    Member

    ...mumble mumble physics mumbles...

    Posted 11 years ago #
  13. Kenny
    Member

    I'm not disagreeing with you, Two Tired - I'm just avoiding the physics debate, as it's over the head of a guy with a finance degree working in IT... I knew I should have studied the sciences more than music at school...

    Posted 11 years ago #
  14. allebong
    Member

    I knew writing indisputable would get me called out, for good reason to be fair. I have enough of a physics background to understand how one would actually analyse the impact on a helmet in a semi-rigorous fashion. This would be quite different to how it's 'analysed' in a typical forum with vague allusions to 'absorption of force' etc. It's a wonderful little example in how your starting assumptions can change the outcome to whatever you want. So, if you assume your head is a rigid mass, and add the mass of the helmet even though it's really quite small compared, then to slow down the head obviously requires application of a force. Assuming a constant deceleration then force is change of momentum over a time required to come to rest, for which it is easy enough to see that increasing the deceleration time reduces the force. A simple way to increase time of deceleration is to have a deformable layer between the impact point and the head. Now, if you agree with those assumptions, and for a simple model of impact you'd have to, then it really is beyond dispute that the helmet has reduced force on the head, otherwise we're having to violate some laws of physics.

    There is of course every reason to dispute any and all assumptions and without sidetracking this too far here's my take: I just can't see a helmet being in any way as rigid as a skull and being able to restrict it's deformation. Heck the whole point of the helmet is to crush which is I understand the opposite purpose of a skull. As for impact time I would say that the time is so short as to be considered 'quasi-constant' which is a fancy way of saying so short that constant deceleration can be assumed. As for increasing diameter, I don't see the few cm increase over the diameter of the head as being all that critical or the difference between life and death. If I get bored I'm going to run the numbers on mass/kinetic energy of the bare head versus one with a helmet to see what the differences are.

    So, I suppose my point is that in my mind it would be very difficult to conceive of a straightforward impact in which the helmet does not reduce force. I'm well aware that a helmet may increase rotational injuries so obviously this isn't the only consideration and makes the point about models/assumptions versus reality all the clearer.

    Still I think the better question is 'how likely are you to hit your head while cycling anyway?' That's a much more important factor than anything else.

    Posted 11 years ago #
  15. sallyhinch
    Member

    Not sure this will add more light or more heat but seems a good summary of the known facts (by Ben Goldacre of Bad Science fame)

    http://www.bmj.com/content/346/bmj.f3817?ijkey=I5vHBog6FhaaLzX&keytype=ref

    EDIT: I see SRD got there first. Sorry!

    Posted 11 years ago #
  16. stiltskin
    Member

    Given that on the CTC forum people could not agree that this incident:
    http://forum.ctc.org.uk/download/file.php?id=21399
    showed a helmet doing its job in this particular instance, I doubt that we will agree on how effective helmets are. As our bovine compadre points out: people's opinions are pretty entrenched.

    Posted 11 years ago #
  17. Baldcyclist
    Member

    OT: But IT does involve some degree of sums and stuff? </OT>

    One thing I often find slightly confusing about citing medical professionals is how we pick and choose which bits of what they say to suit our own beliefs, for example:

    Oncology Consultant: In my professional opinion, based on years of experience, and seeing the results of many autopsies involving smokers, there is a direct correlation between smoking and cancer.

    General population believes statement.
    85 y/o male smoker: I've smoked 40 a day since I was 14, and look at me, I'm fine.

    A&E Consultant: In my professional opinion, based on years of experience, and seeing the results of many accidents involving cyclists both with, and without helmets being worn. I conclude that helmets are worth wearing.

    General population believes statement.
    35 y/o female cyclist: I never ware one, they look silly and I don't like them, and look I'm still fine.

    Posted 11 years ago #
  18. wee folding bike
    Member

    Two tired, how do you absorb a force? I'm unclear on how the helmet mass cancels out.

    allenong, the foam seems fairly rigid and when hit by a truck doesn't crush, it cracks. On the diameter thing I know when I did use one I banged the garage door a lot. The last time I looked the fashion seemed to befor hats which stick out a lot at the back.

    Not likely to hit your head. There is that Dutch video of people falling over on ice. I know I've only hit my head on the road once. The plastic hat didn't help with that one.

    Posted 11 years ago #
  19. Nelly
    Member

    Cant decide which to wear tomorrow

    Posted 11 years ago #
  20. Baldcyclist
    Member

    If we don't believe polystyrene sheathed in plastic has any effect in absorbing force, perhaps we should lobby the motoring industry to stop wasting money putting bumpers on cars?

    Posted 11 years ago #
  21. wee folding bike
    Member

    My bumpers are steel with a plastic cover.

    Thinks… might be aluminium.

    Posted 11 years ago #
  22. Baldcyclist
    Member

    Few years ago, someone drove into the back of my Volvo, cracked the plastic. Could see the foam through the plastic.

    Posted 11 years ago #
  23. Nelly
    Member

    Baldcyclist, I take it you threw out the car as it had damaged the entire space time fabric of the whole thingy (or whatever it is helmet makers tell us !!)

    Posted 11 years ago #
  24. Baldcyclist
    Member

    No, but it did get a shiny new foam covered plastic bumper, and the shock absorber piston thingmies that were attached to it.

    The 'helmet' did it's job in redirecting the force, and the car was able to live another day after the 'helmet' was replaced. ;)

    Posted 11 years ago #
  25. wee folding bike
    Member

    Ahhhh, one of those modern front wheel drive Volvos? I've got a 940 wagon. A Focus destroyed its front end against our back bumper and it did scratch the plastic cover.

    Posted 11 years ago #
  26. Baldcyclist
    Member

    It was a S60, have a V70 now. Same story, for us, Boy racer Suburu Impresa drove into us. I thought I had stalled the car, got out, wee crack on the bumper, front end of Suburu, gone. <promise, end of OT now>

    Posted 11 years ago #
  27. Two Tired
    Member

    @ wee folding bike

    By the same rule you were referring to. Slightly more mass = slightly more kinetic energy (for a given speed). Just as slightly more mass = slightly larger force required to bring said mass to a standstill. It is the whole reason we cant all be superman and stop trucks with our bare hands :-)

    Posted 11 years ago #
  28. Baldcyclist
    Member

    "doesn't crush, it cracks."

    What causes it to crack? Heat.
    What causes heat? Energy.
    Where would that energy otherwise have gone? Head.

    Posted 11 years ago #
  29. Uberuce
    Member

    Baldcyclist, the oncologist is being an eejit to trust their personal experience over the monkeybuttloads of epidemiological evidence supporting that statement, even though it agrees.

    There isn't that same level of evidence to support the A&E consultant's statement, or else you'd have cited that instead, methinkles.

    Posted 11 years ago #
  30. wee folding bike
    Member

    Two tired,

    Why did you use energy in one line and force in the next?

    Still not clear on the cancelling thing.

    Posted 11 years ago #

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