Research into helmet compulsion

[very-near]

Leverage. Instead of the force being applied at distance x from the pivot it's applied at x + y where x is the radius of the head and y the thickness of the helmet.

So what you are saying is that a baby has less chance of getting brain damage than an adult if they fell onto a hard surface fro the same distance because it has a smaller head ?

A helmeted head has a much slower deceleration curve in an impact than an unhelmeted head.

The distances involved in the thickness of a styrene lid is not going to make that much difference when your head hits tarmac at 4 metres a second.

 

[MartinC]

None of us are in a position to 'apply rigour' to the facts of that particular case, because we're not privy to them.

What we can do is look at the general factors.

So far as I can see, nobody disputes that helmets sometimes help and sometimes don't. The arguments relate to the proportion of each case, and we're all speculating there.

Absolutely agree. Nobody knows if, when or how much they help. Nobody will be able to know this in any particular case either.

This why I don't think the contributory negligence thing is going anywhere.

All we do know is that large population studies show no benefit from wearing cycle helmets but many people continue to tell us that we should wear them.

This thread started with a post about of the model that had been produced to calculate the cost to a population of introducing compulsory cycle helmets.

 

[MartinC]

So what you are saying is that a baby has less chance of getting brain damage than an adult if they fell onto a hard surface fro the same distance because it has a smaller head ?

A helmeted head has a much slower deceleration curve in an impact than an unhelmeted head.

The distances involved in the thickness of a styrene lid is not going to make that much difference when your head hits tarmac at 4 metres a second.

You misunderstand.

 

[CopperBrompton]

The argument about torsional injuries is that the larger effective diameter of the helmeted head generates greater rotational forces.

However, this doesn't take into account the fact that the friction from the scalp is much, much greater than the low-friction surface of a slippery helmet shell.

Taking both into account, I'd expect the rotational forces to be substantially higher without the helmet.

 

[CopperBrompton]

Absolutely agree. Nobody knows if, when or how much they help.

That's not quite accurate. There is no 'if' - in some proportion of cases, a helmet definitely helps. 'How much' is also measurable after the event, though not predictable beforehand. 'When' is, of course, totally unknown: in some events, it will help, in others it won't, and we can't predict which will be which.

This why I don't think the contributory negligence thing is going anywhere.

I think that depends on the sums of money involved. Given an accident leaving someone needing 24/7 care for life, it would be worth an insurer spending the cash to do the measurements and hire the relevant experts.

But I'd agree that won't be worthwhile in most cases.

All we do know is that large population studies show no benefit from wearing cycle helmets

As you know, there are conflicting conclusions from different studies.

but many people continue to tell us that we should wear them.

Not me. I'll tell anyone why I wear one, and I'll chip in when I see a one-sided argument, but I believe totally in personal choice.

 

[MartinC]

The argument about torsional injuries is that the larger effective diameter of the helmeted head generates greater rotational forces.

However, this doesn't take into account the fact that the friction from the scalp is much, much greater than the low-friction surface of a slippery helmet shell.

Taking both into account, I'd expect the rotational forces to be substantially higher without the helmet.

All speculation. I don't know what the co-efficients of friction are for the surfaces involved. There is a theory that evolution has kept hair on our heads (well some of us anyway) because it's low friction and there's an advantage in avoiding head injuries.

It's complicated further by snagging points - vents, broken helmets etc. If these create the possibility that something may catch on the surface that's struck friction is the least of your problems.

 

[very-near]

You misunderstand.

I understand that rotational forces cause spinal injuries, but most impacts are either direct or glancing blows, and are compression impacts not torsional ones.

It is the bit where the brain marches forward in the skull and gets squashed at one end (ripping the blood vessels) which causes the most damage as I understand it, and these are caused by fast decelerations where the brain can't keep up.

 

[MartinC]

I understand that rotational forces cause spinal injuries, but most impacts are either direct or glancing blows, and are compression impacts not torsional ones.

It is the bit where the brain marches forward in the skull and gets squashed at one end (ripping the blood vessels) which causes the most damage as I understand it, and these are caused by fast decelerations where the brain can't keep up.

You're right it's the severing of blood vessels and nerve connections that causes brain damage. It's rotational blows that cause a disproportionate amount of this because they create shear forces between parts rotating with different accelerations. Direct blows are more benign - the brain compresses and then recovers with less chance of damaging connections.

 

[very-near]

You're right it's the severing of blood vessels and nerve connections that causes brain damage. It's rotational blows that cause a disproportionate amount of this because they create shear forces between parts rotating with different accelerations. Direct blows are more benign - the brain compresses and then recovers with less chance of damaging connections.

Hey Ho, this makes sense. I still think my cycle hat has a lower friction coefficient than my scalp or the underlying bone.

We need a phrenologist on here now to offer a bit more info on this area.

 

[magnatom]

You're right it's the severing of blood vessels and nerve connections that causes brain damage. It's rotational blows that cause a disproportionate amount of this because they create shear forces between parts rotating with different accelerations. Direct blows are more benign - the brain compresses and then recovers with less chance of damaging connections.

I can confirm that this is true. Rotational head injuries are more serious that direct blows to the head.

 

[magnatom]

Hey Ho, this makes sense. I still think my cycle hat has a lower friction coefficient than my scalp or the underlying bone.

We need a phrenologist on here now to offer a bit more info on this area.

I think this is what the pro-choicers (myself included) are getting at. It isn't clear cut at all, and although 'common sense' might suggest that a helmet prevents head injuries, the reality is not as simple.

I wear a lid, by the way.

 

[very-near]

I can confirm that this is true. Rotational head injuries are more serious that direct blows to the head.

I watched a program on the development of the HANS device a few years ago for racing drivers. It has saved a lot of lives as it protects the wearer from Basilar skull injuies

 

[Dan B]

All speculation. I don't know what the co-efficients of friction are for the surfaces involved. There is a theory that evolution has kept hair on our heads (well some of us anyway) because it's low friction and there's an advantage in avoiding head injuries.

This should be fairly simple to measure, though, and without vegetablising the test subjects.

 

[Greenbank]

The argument about torsional injuries is that the larger effective diameter of the helmeted head generates greater rotational forces.

The increased effective diameter can have a much more profound and direct effect. Obviously an exaggeration but I hope it will illustrate my point; Compare (in your mind, don't try this at home kids) doing a forward roll with nothing on your head to doing a forward roll with a traffic cone firmly attached to your head.

Or, tilt your head as far forward as you can go, right on the limit of it being painful. Now imagine it being pushed a further 1" forward. Repeat for head tilted back or to the side (sounds like the scene from JFK...back and to the side....back and to the side).

 

[MartinC]

A lot of the knowledge has come from medical studies of boxing injuries. I believ they modified head guards and re-emphasised the importance of gum shields on the back of it. It's why rugby players wear gum shield now - they use more of the neck and jaw muscles to stop the head rotating on impact. Maybe cyclists should wear them.