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So I am sitting here watching some college football and had a thought.. their helmets are designed to take severe impacts repeatedly right? RIGHT... so my question is why are our helmets only designed for one impact then rendered useless. I know all about how the foam inside seperates and it is not advised to be worn again but why cant they come up with a mix between the two? You may think this post is stupid BUT I have always belived that the only stupid question is the one that is never asked.
 

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Not a stupid question really. I would imagine the answer being something close to the fact that the collisions in most football tackles are not as bad as when a motorcycle helmet hits the pavement at speed.
 

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Not a stupid question really. I would imagine the answer being something close to the fact that the collisions in most football tackles are not as bad as when a motorcycle helmet hits the pavement at speed.
Yep, the energy of impact is proportional to speed^2. So (painting with really broad strokes here) a running man will run at maybe 15 mph; much slower for a linebacker butting heads with another linebacker at the scrimmage line. A cycle helmet has handle highway speeds at the very least, which is 4x that fast. 4^2 = 16 times the energy absorption in the cycle helmet.

You might be interested to know that a car racing helmet is rated for multiple impacts, and fire resistance, plus the energy absorption of a motorcycle helmet. That's the difference between Snell ratings Mxxxx and SAxxxx, where xxxx is the year.
 

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lol i definitely dont think this is a stupid question. a helmet that was just as safe after 2-3 impacts would be awesome
 

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Snell rated helmets at least ARE rated to take multiple hits, it's just not a good idea.
 

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Yep, the energy of impact is proportional to speed^2. So (painting with really broad strokes here) a running man will run at maybe 15 mph; much slower for a linebacker butting heads with another linebacker at the scrimmage line. A cycle helmet has handle highway speeds at the very least, which is 4x that fast. 4^2 = 16 times the energy absorption in the cycle helmet.

You might be interested to know that a car racing helmet is rated for multiple impacts, and fire resistance, plus the energy absorption of a motorcycle helmet. That's the difference between Snell ratings Mxxxx and SAxxxx, where xxxx is the year.
I found a flaw in my own reasoning. As long as the helmet slides along the ground, the energy of impact is only a fall from 5' in the air or so, and you can almost ignore the forward velocity. So it is probable that bike helmets are designed for MUCH less than 16x the energy absorption of a football helmet.

Still, I am convinced it is an energy absorption thing. But also convinced I'm off on the magnitude of it. Got excited by the physics, I guess.
 

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Motorcycle helmets, by design, are vastly more protective.

Because of that vast amount of protection, they sacrifice the ability to repeatedly absorb impact.

Forward velocity is rarely related to impact velocity of a helmet (see acceleration of gravity), and when it is no amount of protection will save the brain.
 

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VERY SIMPLE ANSWER


Cushioning designed for a single impact will absorb more energy than cushioning designed for multiple impacts


Due to the velocity of a bike impact, you need more cushioning. To do this with reusable cushioning, such as polyethylene or polyurethane, you would need a much thicker cushioning - several inches thick


I'm a packaging engineer, I design reusable cushioning for a living - I'm typically using 2 to 4 inches of reusable foam for a typical 24" to 48" drop.
 

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So I am sitting here watching some college football and had a thought.. their helmets are designed to take severe impacts repeatedly right? RIGHT... so my question is why are our helmets only designed for one impact then rendered useless. I know all about how the foam inside seperates and it is not advised to be worn again but why cant they come up with a mix between the two? You may think this post is stupid BUT I have always belived that the only stupid question is the one that is never asked.
Have you seen those quarter backs that have a double helmet design via excessive concuchions ?

That should show the limited effect that football helmets have
 

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When I played football (just in highschool), all the helmet had was its hard kind thick plastic on the outside and some "air-bags" on the inside so you could pump it up or down to make it fit better.
 

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I'd imagine they get new helmets every season. So they last 13 games, plus play offs.
nope the only time a helmet will be replaced is if the shell is cracked. i had the same helmet for 5 years in college, they hold up very well.

Just a FYI my running speed was roughly 20mph and most impacts i had were at that speed from Kick coverage. 15mph is very very conservative, you would also have to calculate the the amount of force generated from the legs. in professional football, i have heard that the force can be equivalent to that of a 25mph car accident.

i say someone should send this into mythbusters.
 

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Cool topic really. Here's the thing, football helmets have to be able to take multiple impacts, they would be useless if they couldn't so there is no permanent compression of the paddign materials. Ideally you're not crashing your motorcycle on a daily basis, so it's been designed to crush inside on impact, very much the same way the crumple zone on the front of a car works to dissipate energy.

Simple fact is you get more protection from something that's going to permanently compress during an impact, and when you crash a motorcycle, having to replace a helmet is well worth having all the protection you can get.
 

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Helmets have something known as EPS which
The great thing about EPS is that as it crushes, it absorbs lots of energy at a predictable rate. It doesn't store energy and rebound like a spring, which would be a bad thing because your head would bounce back up, shaking your brain not just once, but twice. EPS actually absorbs the kinetic energy of your moving head, creating a very small amount of heat as the foam collapses.
This thing works only once, so even if you manage to drop your lid on concrete/asphalt from 3 feet or above, your helmet is a goner the EPS has done its work and is of no use in case of an impact.
Source--
Helmet Performance: Blowing the Lid Off - Motorcyclist magazine
 

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I'm not sure why anyone would want a helmet designed to be crashed multiple times. Does anyone think this guy got up, removed his helmet and thought "Damn, I could keep wearing this if only it was designed for multiple impacts"?
 

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For car racing, you do want a multiple hit rating. The liner is a very similar material to motorcycle helmets, so I would be very interested to know the difference that allows multiple hits to one but not the other.
 

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Snell rated helmets at least ARE rated to take multiple hits, it's just not a good idea.
Yep, they are tested for 2 impacts to the same spot. The foam is permanently distorted after each though. Keep in mind when making comparisons that a football helmet is designed to be crashed into other players and a grass field only, both significantly softer and at lower rates of speed than a motorcycle on asphalt. The idea behind motorcycle helmets is to try to prevent permanent brain injury in a wide variety of situations. A football helmet only has to protect from one situation.


as common as concussions are in football, i'm not so sure those helmets really do much
Pretty much what I was thinking. The padding in a football helmet is just a cushion, and a soft one at that. it doesn't take a huge hit to fully compress that padding and once you do, you've got nothing left. A motorcycle helmet has much a much harder shell, which while not a fun thing to crush over your head, will provide a lot more protection in a major impact.
 

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I'm not sure why anyone would want a helmet designed to be crashed multiple times. Does anyone think this guy got up, removed his helmet and thought "Damn, I could keep wearing this if only it was designed for multiple impacts"?
Just needs a new visor *shrug* It doe snot look like it took an impact more of a slide.

Yep and forget half helmets:


Of course plastic bags are the best way to go:
 

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nope the only time a helmet will be replaced is if the shell is cracked. i had the same helmet for 5 years in college, they hold up very well.

Just a FYI my running speed was roughly 20mph and most impacts i had were at that speed from Kick coverage. 15mph is very very conservative, you would also have to calculate the the amount of force generated from the legs. in professional football, i have heard that the force can be equivalent to that of a 25mph car accident.

i say someone should send this into mythbusters.
NFL vs College.

in the NBA they get new shoes every game.
 
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