Helmets – again

madcarew wrote:

maviczap wrote:

No matter how good the helmet, it does nothing to prevent the brain bashing against the inside of the skull, because of the massive deceleration forces involved in any crash. It will help prevent the skull breaking but not the bruising to the brain, and swelling of the brain which is what’s going to cause problems.

 

That is precisely what it helps prevent, by providing a crumple zone, which provides a deceleration zone. Helmets aren’t to stop the skull being broken (the skull is much much stronger than a helmet) it provides a crumple zone, much like on your car. When your head hits the ground there is no deforming material that will absorb any energy, so the skull undergoes a massive deceleration (deceleration is inversely proportional to the distance available for deceleration) so if your helmet provides 5 mm of deformation compared to 1mm of deflection of your skull, then you have reduced the brain’s deceleration to one fifth. If the original deceleration was 50g, which is undoubtedly traumatic, you have reduced it to 10g, which is probably no more than banging your head hard against a table.

And yet so often we see broken/split/cracked helmets were that has not occured at all. That ‘crumple zone’ as you put it is sometimes effective at low speeds but only proven so in very strange and ‘best case’ scenarios, like falling onto the top part of your head onto a flat stationary surface from a walking speed and even then it will often not be enough to prevent a concussion or serious head injury. The vast majority of the forces will have been absorbed by the skull/brain.

The evidence proves precisely that helmets rarely ever prevent what you are trying to establish based on theoretical numbers in a lab/test environ which are rarely ever replicated in real life. this is in part why helmets fail so badly to have an effect on safety.

You cotinue to ignore the fact that many head strikes would never occur at all if a helmet were not worn, you continue to attribute any saved life/head injury as being the result of helmets just liuke Rich_cb does. 

Again the data revealed in the Virginia study clearly states that despite big increases in helmet wearing deaths/injuries are at a high since 1991 and that almost half of all dead cyclists were wearing helmets, that’s hardly an indication of increased safety through helmet wearing is it?

Want to check the stats for Canada, I did, injuries/deaths have risen since helmet wearing became a thing, there’s a massively high % of helmet wearing in Canada, it’s not improved matters it’s made it worse.

Keep believing your hypothetical numbers, it’s total pony and the deaths and injuries to people on bikes keep mounting up, people like you and others are dangerous, not just to yourselves but the rest of us too and sadly that not just with regards to head injuries but all types of injuries as well as the other massive negative effects helmets have on people on bikes.

Deeferdonk wrote:

flobble wrote:

Deeferdonk wrote:

Jimmy Ray Will wrote:

Cracked a helmet once, dropping it from waist height on to a flat surface. Are there any physics experts that could calculate the sort of energy a 250gram object falling from 1m would generate before impact? I can’t help but feel that it wouldn’t be a lot. 

Well thinking back to GCSEs

F =MA  =0.25 x 9.81 = 2.45Newtons of force

Er, no.

OP asked for *energy*

Gravitational potential energy converted to kinetic energy = mgh = 0.25 x 9.81 x 1 = 2.45 joules

Whether that cracks a helmet depends a bundle of other things: the time duration of the impac (affects the decceleration and hence the force applied to the helmet), how concentrated the resulting force is, the shape of the helmet in the impact area, whether there’s prior damage you didn’t see, etc, etc…

Well, the energy it takes is a bit meaningless ( how many calories is your helmet rated at!?), so i interpreted what he really was asking for was force . As you go on to explain in your post, it’s the force and how its applied that is actually meaningful to the capacity of a helmet..

Actually it’s the energy dissipation that is important. The helmet is designed to work whilst wrapped around a head, not whilst empty. Hence Jimmy’s ‘test’ has no relevance to the efficacy of a helmet. It is highly likely that had the helmet been filled with a melon when he dropped it, it wouldn’t have broken, despite being 10 times heavier and the force 10 times greater.

Also, it is difficult to concieve that a helmet in good condition would break under the conditions that Jimmy describes, so it is possible, likely even, that it was already compromised.

maviczap wrote:

No matter how good the helmet, it does nothing to prevent the brain bashing against the inside of the skull, because of the massive deceleration forces involved in any crash. It will help prevent the skull breaking but not the bruising to the brain, and swelling of the brain which is what’s going to cause problems.

 

That is exactly what the research was investigating, as does some existing tests.

flobble wrote:

Deeferdonk wrote:

Jimmy Ray Will wrote:

Cracked a helmet once, dropping it from waist height on to a flat surface. Are there any physics experts that could calculate the sort of energy a 250gram object falling from 1m would generate before impact? I can’t help but feel that it wouldn’t be a lot. 

Well thinking back to GCSEs

F =MA  =0.25 x 9.81 = 2.45Newtons of force

Er, no.

OP asked for *energy*

Gravitational potential energy converted to kinetic energy = mgh = 0.25 x 9.81 x 1 = 2.45 joules

Whether that cracks a helmet depends a bundle of other things: the time duration of the impac (affects the decceleration and hence the force applied to the helmet), how concentrated the resulting force is, the shape of the helmet in the impact area, whether there’s prior damage you didn’t see, etc, etc…

Well, the energy it takes is a bit meaningless ( how many calories is your helmet rated at!?), so i interpreted what he really was asking for was force . As you go on to explain in your post, it’s the force and how its applied that is actually meaningful to the capacity of a helmet..

fukawitribe wrote:

No, I don’t think there is no risk compensation in sport – quite the opposite .

It’s an interesting topic. I’m not sure how much of this is strict ‘risk compensation’ and how much is just evolution of the game and other factors… but there are definitely unintended consequences of more padding, and I’d take a punt on some of it being attributable to risk compensation. It must be really difficult to measure in a competitive environment with risks being taken anwyay.

But, a couple of examples:

Old school American Football having skull-caps to protect the head. Toughen up the helmets to become the motorbike-like ones they have today… players start tackling, ram-style, with their heads. Big news at the mo due to concussion, depression, and potentially massive lawsuits against the NFL.

Boxing: old-time bare-knucklers lasting 100+ rounds with few headshots due to the risk of broken hands. Today: 10oz+ gloves, 12 rounders (tops); broken hands are a regular scourge.

Amateur headguards were removed for male competition after 30 years of being mandated. The rationale was that they didn’t decrease head injuries – in fact, increased head injuries owing to less focus on defence and increased risk taking is one of the main reasons given: https://www.iseh.co.uk/news/latest-news/new-page-44

They now have the weird situation where women do wear headguards and men don’t, but, as the reason given for that is they don’t have the evidence for women yet as it’s a relatively young sport, and don’t just want to follow the men, it does at least hint at it being an evidence-based rule.

Deeferdonk wrote:

Jimmy Ray Will wrote:

Cracked a helmet once, dropping it from waist height on to a flat surface. Are there any physics experts that could calculate the sort of energy a 250gram object falling from 1m would generate before impact? I can’t help but feel that it wouldn’t be a lot. 

Well thinking back to GCSEs

F =MA  =0.25 x 9.81 = 2.45Newtons of force

Er, no.

OP asked for *energy*

Gravitational potential energy converted to kinetic energy = mgh = 0.25 x 9.81 x 1 = 2.45 joules

Whether that cracks a helmet depends a bundle of other things: the time duration of the impac (affects the decceleration and hence the force applied to the helmet), how concentrated the resulting force is, the shape of the helmet in the impact area, whether there’s prior damage you didn’t see, etc, etc…

Cracked a helmet once,

Cracked a helmet once, dropping it from waist height on to a flat surface. Are there any physics experts that could calculate the sort of energy a 250gram object falling from 1m would generate before impact? I can’t help but feel that it wouldn’t be a lot. 

No, I don’t think there is no

No, I don’t think there is no risk compensation in sport – quite the opposite – although you may want to ask what age group the race was. I did wonder whether you’d ever watched BMX though, or remembered what it was like to be young, or combinations; it was quite interesting you thought you had much influence on how you fell in a BMX race which regard to head strike. You also might want to consider that risk perception and why people racing would want to take a potential performance hit against their competitors. Also have a look at the effect of anxiety on motor skills, a flip-side to over-confidence, interesting..