Helmets, Accidents and NOT Removing a Helmet

[Tonyf33]

In a recent accident, my helmet was removed very, very carefully by members of the emergency services while at the same time supporting my neck. I was told firmly at the outset - and several times afterwards - that when asked a question, to answer yes or no but NOT SHAKE OR NOD MY HEAD!

So guess the answer is -leave it to the medic/firemen or whatever trained person is doing it.

NB the hat did something for me that no amount of statistics would have done - I still have it, with the yellow paint from the trucks bonnet on it! And I have my head too, in one piece, unharmed (apart from a bit of faint bruising on my temple that is)!

How do you know that the hat didn't induce you into riding less safely, how do you know that the hat didn't have an influence on the position of your head in relation to the bonnet, how do you know that you might not have struck the bonnet at all without a helmet due to the extra weight and circumference?
You still got injured, how can you know that you would have had any head injury at all without or one that was the same? No doubt a bruised head without wearing a helmet would have come in for criticism and shouts of 'luck' etc whereas the same bruise wearing one is a helmet saved my life incident
No anecdotal stories prove anything and statistics do indeed show that people espousing the benefits of helmets fail to understand the limitations and indeed the downsides to wearing helmets that cause higher rates of head injuries over those not wearing them.

[Shootist]

I've performed CPR a couple of times. The first was on an old chap and I believe from the sounds issued that I did just about every rib attached to the sternum! But he survived a couple of days in coronary Care Unit and was able to bid his wife farewell, for which I got a lovely letter from her, thanking me for my efforts..

[Cunobelin]

Some fall off on their own during the impact!

That's what's known as a 'feature'. It splits in half on impact to allow for easy removal.

Or a "failure" when you look at snag points strap s failing and ejection?

A helmet that splits in half has failed to offer adequate protection... full stop

Even more ridiculous is that when helmets are tested they are allowed to tape them to the "form" using heavy duty tape

Hardly reflects reality.... unless taping the helmet to your head with high quality industrial tape becomes standard practice

[Cunobelin]

Sounds silly, but CPR is not just for the patient....

We were called because we were known to work in a hospital to a local address

When we got there the patient was beyond help

However we still did CPR and called the ambulance

It was a performance that allowed the relatives to think that they had done all they could

Imagine how they would have felt if we had arrived, said "you left it too late" and walked off

[TonyR]

Hardly reflects reality.... unless taping the helmet to your head with high quality industrial tape becomes standard practice

Sshhusshh or you'll be giving people ideas!

[rmurphy195]

A helmet that splits in half has failed to offer adequate protection... full stop

Dangerous talk I know, but I'd have to disagree with that one - having seen it happen, the person concerned went head-first into tall railings, the cyclists hat split in two but she was unharmed. Well, her head was anyway, the rest was just shock and bruises. I guess the hat worked a bit like the crumple zone on a car - self destructed but absorbed the energy of the impact. I guess this ended up as a statistic somewhere from the ambulance medic's report.

The lesson she earned I think was to not turn up for hilly rides on a folding shopper with steel rims !

[[XAP]Bob]

Crack = failed

The crumple zone effect is real, but the hat has to crush for that to happen.

[kwackers]

I guess the hat worked a bit like the crumple zone on a car - self destructed but absorbed the energy of the impact. I guess this ended up as a statistic somewhere from the ambulance medic's report.

Crumple zones on cars work by - well, crumpling. Imagine that instead of crumpling they split to let the passengers out, you wouldn't consider them to have worked then would you?

Hats behave in the same way, up to a point they crumple then when you exceed their meagre limits they split and the reason they split is to allow the shell to move out of the way and let your head through.
Wait! I hear you say, if her head went through why isn't she cabbaged? Well, turns out that her skull is about 10 times stronger than her lid so even if the helmet fails it doesn't necessarily mean she'll smash her head apart.

Here's a simple experiment for seeing how catastrophic failure works.
Pump up a balloon. Now clench the knot in your knuckles and hit a wall, hard but not hard enough to burst the balloon. Nice init? You could hit that wall all day.
Now increase the force slightly with each punch up until the point that the balloon bursts. What you'll find is that the penultimate punch was just as nice as the others and then suddenly - broken knuckles! And yet the difference in force was tiny, so surely the balloon should have absorbed nearly all the energy and you should have just lightly tapped the wall?
Sadly no and helmets behave in the same way, right up to the point they split they do a decent enough job absorbing energy and then at the point they split they do virtually nothing.
But the good news is that as I mentioned your skull is significantly stronger so even though the helmet fails you can still walk away.

[[XAP]Bob]

Good balloon analogy

[rfryer]

Interesting balloon analogy! Assuming you were gradually increasing pressure with every punch, the burst would presumably happen when your fiat was almost stationary, and so broken knuckles would be unlikely.

I think this is even more the case with polystyrene; if you taped a bit to the wall, then hit it increasingly hard until it cracked, I'd be surprised if the final punch caused significantly more pain than the one before.

Maybe I'm wrong, but I doubt it. If I had a piece of polystyrene lying around I'd give it a try.

[rfryer]

Thinking about this further, my issue is with the oft-stated opinion that cracked polystyrene means that the helmet "failed" and no impact was absorbed. In fact, surely a good deal of energy could have been absorbed before the point of cracking, and more may have been absorbed afterwards if the other structural parts of the helmet had held the cracked parts together.

[Vorpal]

Thinking about this further, my issue is with the oft-stated opinion that cracked polystyrene means that the helmet "failed" and no impact was absorbed. In fact, surely a good deal of energy could have been absorbed before the point of cracking, and more may have been absorbed afterwards if the other structural parts of the helmet had held the cracked parts together.

I'm sorry, but polystyrene absorbs almost no energy in shear or bending (the kind of forces that cause it to crack or break). It only absorbs energy in compression.

And once it has broken, although pieces can still absorb energy in compression, they need to be in place to do so.

As others have said, a cracked helmet is evidence of a failure. It may have absorbed a little energy, but likely that went into cracking the shell.

In all probability, the worst your friend would have had without her helmet is a sore head.

[[XAP]Bob]

Thinking about this further, my issue is with the oft-stated opinion that cracked polystyrene means that the helmet "failed" and no impact was absorbed. In fact, surely a good deal of energy could have been absorbed before the point of cracking, and more may have been absorbed afterwards if the other structural parts of the helmet had held the cracked parts together.

If the now separate pieces show evidence of significant crushing, then yes - but I'm yet to see pictures of a cracked cycle helmet showing such deformation.

Next time you have some packaging try squashing the expanded polystyrene - it takes significant effort, this effort is applied across a distance equivalent to ~2/3rds (IIRC) of the thickness of the material - force * distance = energy absorbed.
Then try snapping it - almost no energy required - the force builds to a certain point, but the fracture is brittle, so that force gets applied across a negligible distance - that's why there is practically no energy absorbed by a fractured helmet.

It's also why there are often reinforcing threads through helmets, to try and hold the pieces together, but they are not there to absorb energy, just to hold the polystyrene packing material in place...

The human head is a marvel of design - and it can cope with far more than most people think.

[kwackers]

Interesting balloon analogy! Assuming you were gradually increasing pressure with every punch, the burst would presumably happen when your fiat was almost stationary, and so broken knuckles would be unlikely.

You'd think wouldn't you?
Try it and report back.

[rmurphy195]

Thinking about this further, my issue is with the oft-stated opinion that cracked polystyrene means that the helmet "failed" and no impact was absorbed. In fact, surely a good deal of energy could have been absorbed before the point of cracking, and more may have been absorbed afterwards if the other structural parts of the helmet had held the cracked parts together.

When I replace my helmets, I tend to destroy the old one so someone doesn't pick it out of the rubbish and use it. And believe me it really, really takes a lot of effort to smash them - dropping bricks and slabs on them, hurling them against walls, jumping up and down on them - its hard work. Until I take a sharp knife to them that is!