# Helmet Discussion - Single vs Multi Impact



## jurichar (Aug 19, 2009)

So, being broke off gives one quite a bit of time to ponder the intrigues of life that elude otherwise preoccupied brain real estate when one has the ability to ride bikes. Combine another broke off rider and it could be possible to become the Stephen Hawkins think tank of all things two wheeled.

The topic for discussion today - Helmets.

The backstory is that me and a buddy are both really jacked right now from similar bike accidents. Both of us made some jumping miscalculations and suffered faceplants. Mine was from over jumping on a dh rig and his from overjumping a DJ. Similar impact zone on the helmet, but vastly different injuries. ( I realize there are a billion factors that go into a crash and no two are ever the same, but it's interesting to discuss nontheless.)

In this crash I was wearing a carbon D2 and leatt combo (single impact rated - EPS), and my buddy was in a POC half lid (multi-impact rated - EPP). I sustained absolutely zero head or neck trauma and remained fully conscious for the entire impact (verified via CAT scan and MRI - the doc didnt believe me either after seeing the helmet). By buddy was not so lucky, he sustained a badly broken neck and a little head trauma (the 10 days in icu variety). We both also broke a boat load of bones 10-20 for me and 4 for him.

We were examining our crash helmets today and made some observations. My carbon D2 was mangled, it is absolutely without a doubt unusable. The carbon is crushed in a 2"x2" patch, the inner foam is completely seperated from the outer shell and is by definition internally "crushed." My buddies POC had a few scratches on the outer shell, but definately no cracks or noticable dents. The inner shell has a few very small (>1cm) stress fractures, but no "crushing" or foam compaction.

So my d2 made of EPS is only rated for one impact, whereas his helmet is EPP and rated for "multi impact." From what I can gather the measurement system for rating a helment for multi-impact means that a helmet needs to mantain its ability to not deteriorate a specific percentage on subsequent crashing incidents. But i'm having a little trouble swallowing this as a good idea for your head in a crash situation... 

(DISCLAIMER: this part is speculation - I have an advanced medical degree, but im not a physicist nor neurologist, so this could be complete rubbish)

When you crash, the point of a helmet is to do two things 1) protect you from a sharp object "high PSI" that could cause a piercing/cracking of the skull bone 2) protect you from a flat object "low PSI" that could cause neck fractures or brain trauma. The means by which this is achieved for either situation is simple...dissipate kinetic energy, i.e. take the newton force created by the impact and move it somewhere that is not your brain/skull/neck. To obtain objective #1 your need a hard outer shell and for objective #2 you need some sort of thicker barrier (foam) to transfer the energy away.

So in an optimal situation, in a crash you want your helmet to absorb/dissipate as much kinetic energy as possible upon impact. According to the law of conservation of energy, the energy dissipated has to go "somewhere." In the case of a single impact helmet the energy goes into the EPS foam which causes it some degree of stress and structural breakdown proportinally relative to the amount of force applied. In a multi impact helmet where does the force go? My understanding is that the materials have a rubber like property that allow the structure to reform or bounce back, but that energy is still contained within the helmet environment, and therefore transferred to the body in a higher percentage than if it were dissipated through helmet destruction. 

It's pretty much common knowledge that in the DH community a helmet is a disposable item. If you're smart you get a new one every year or possibly every two if you had a great season (or you're a sissy  ). I know a few guys that have gone through 1 a month for awhile. I'm having a hard time believing that multi-impact helmets are not marketing schenanigans designed for people who think that $350 - $500 is too much for a disposable item. And i think im subscribing to the idea that single impact helmets are "safer" than their multi-impact counterparts.

Discuss/Flame


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## m3t4w0rm (Aug 1, 2010)

Honestly I will replace a helmet with any direct contact with the ground. If I can feel a indentation then I will get a new helmet. If I kind of bounce lightly off the ground then no I'll wear that helmet again.

If I don't feel confident in the helmet after a crash then its not worth keeping.

Now if I end up smashing the front in then it becomes artwork on my wall.


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## bullcrew (Jan 2, 2005)

9' drop to head - concussion, fractured wrist, seperated rib and water on knee. Helmet shattered blew pieces off shattered jaw etc and the impact was on top.
Still rode out and rode the rest of the day with the hucker lid.

Urge down-o-matic 1 hit wonder needs replacing.

















Will run another or d3 in a heart beat definently saved my life no leate brace had a bruise shaped like the jaw line on my chest.


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## SHIVER ME TIMBERS (Jan 12, 2004)

even if the helmet looks alright after a crash it has lost some of it's absorb/dissipate energy properties

with minor dings keep helmet....any major hits or getting your bell rung....buy a new helmet...your life is worth more then trying to save a few dollars on a compromised helmet


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## bullcrew (Jan 2, 2005)

SHIVER ME TIMBERS said:


> ..your life is worth more then trying to save a few dollars on a compromised helmet


X2, x3, x4

This right here is the right answer


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## 62kona (Mar 25, 2008)

Oh my God bullcrew! I've never seen that much damage to a bike helmet before!


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## bullcrew (Jan 2, 2005)

62kona said:


> Oh my God bullcrew! I've never seen that much damage to a bike helmet before!


Lol I've never tasted pain till then and it tasted like electrical metallic taste.

The other side is blown out as well and there's stress cracks over the rest of it.


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## jurichar (Aug 19, 2009)

I think my point may be getting missed. I completely agree to the theory of replacing a helmet after a heavy crash or if the helmet sustains a massive insult. The point i'm trying to make is what type of helmet is safer to purchase and wear in a crash. An eps single impact rated helmet like bullcrew's (epic blowout btw) will explode upon impact, which may have saved his life; whereas an EPP multi-impact rated helmet like the poc cortex DH would have maintained its structural integrity much better (giving the illusion that the helmet is "stronger" and the exploded one is "weaker").


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## mykel (Jul 31, 2006)

From memory so probably not entirely correct. I seem to have been dropped/fallen on me head a bit too much for gospel.

The EPP helmets are rated for multi impacts, but at a lower threshold. 
The EPS helmets are rated for a single large impact.

The comprimise, is that with an EPS a couple little crashes and it should be replaced. With the EPP it is built to withstand the little crashes....however when the big one comes, the EPS is better at protecting yer melon than the EPP.

ASSuMEing the helmets are of a similar rating, and both never crashed.

michael


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## SHIVER ME TIMBERS (Jan 12, 2004)

mykel said:


> From memory so probably not entirely correct. I seem to have been dropped/fallen on me head a bit too much for gospel.
> 
> The EPP helmets are rated for multi impacts, but at a lower threshold.
> The EPS helmets are rated for a single large impact.
> ...


agree

all helmets will be fine with little crashes....but you replace after big ones...even the EPS helmets will take the little hits

my money is always on the EPS...it still takes the small ones...but I want it for that one big hit.. I don't want to be slobbering around my mouth everyday...just at the strip club


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## chauzie (Mar 8, 2010)

jurichar said:


> ..........
> 
> In a multi impact helmet where does the force go? My understanding is that the materials have a rubber like property that allow the structure to reform or bounce back, but that energy is still contained within the helmet environment, and therefore transferred to the body in a higher percentage than if it were dissipated through helmet destruction.
> .......


This is only partially correct. The impact energy goes into deforming the material (rubber in the case you mentioned above). In either EPS or EPP helmet, the energy is still contained within the system. The only way for energy to exit the system is if the helmet blow up into pieces (ala Formula1 car crash). Otherwise, the energy is not going anywhere (actually it goes into your body in the form of broken neck).

A good helmet design will have to compromise between the need to protect from puncture and the need to disperse energy.

I think the practical solution here is to run a motocross helmet with thick padding. Sure it's a little heavier (not much, probably 1/2 pound), but you're going DH, not climbing in them, so..


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## Fix the Spade (Aug 4, 2008)

jurichar said:


> . But i'm having a little trouble swallowing this as a good idea for your head in a crash situation...


I hope your buddy recovers, breaking vertebrae sucks.

Regards 'multi impact' helmets, read the paperwork, I've had a couple of multi impact helmets (two from Pro Tec, one POC) and the multi only refers to multiple impacts within a single crash. The manufacturers still say you should replace the helmet after a significant impact.

Speaking of which, one Pro Tec didn't fit, the second argued with a tree branch (tree won) and the POC died during a wash out that resulted in nutting the floor at speed...


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## jurichar (Aug 19, 2009)

Fix the Spade said:


> Regards 'multi impact' helmets, read the paperwork, I've had a couple of multi impact helmets (two from Pro Tec, one POC) and the multi only refers to multiple impacts within a single crash. The manufacturers still say you should replace the helmet after a significant impact.
> QUOTE]
> 
> Interesting, this is not how the concept was sold to me by two poc reps. Not even close, actually, the single crash thing was completely left out. Are you sure about this? Im having trouble imagining a mountain bike crash scnerio where you would have two head impacts with similar forces applied. I could see maybe in a car...Windshield>tree/ground, but how would this play out in biking?


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## wookie freeride (Apr 10, 2007)

*one nd done for me to...*

Helmet... much cheaper than hospital.

unless you a Canadian.

Stupid Obama Care :ciappa:


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## rocketmatt17 (Sep 10, 2007)

ive always followed the rule of if you ring your bell you replace the helmet. I did this my first race with a new urge helmet at windham. It doesnt look as bad as bullcrew's but it did crack the helmet just above my right eye. i dont think i would be comfortable using a multi use helmet as tests in the lab and in the field are never the same. I do like the application of new technology to improve helmet designs and not just new shapes. Was your friend wearing a leatt by the way?


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## jurichar (Aug 19, 2009)

no leatt, he owns one but doesnt wear it dj'ing. his lid was a halfie also, not a full face


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## rocketmatt17 (Sep 10, 2007)

> no leatt, he owns one but doesnt wear it dj'ing. his lid was a halfie also, not a full face


You guys heal up fast


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## ryan_daugherty (Oct 8, 2006)

SHIVER ME TIMBERS said:


> even if the helmet looks alright after a crash it has lost some of it's absorb/dissipate energy properties
> 
> with minor dings keep helmet....any major hits or getting your bell rung....buy a new helmet...your life is worth more then trying to save a few dollars on a compromised helmet


either that or send it to the company you bought it from. I did w/ TLD after i clocked my dome from what i thought was hard and they looked at it and sent it back saying it was good to go... quick too.


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## DurtGurl (Dec 10, 2001)

I've now had two bad experiences with a POC. Last year at Whistler, I landed on my right temple and shoulder on A-Line. I only know this from the damage to the helmet and my body, as I was knocked out cold and have no memory of the crash. But that's A-line and we all know how stinking fast you can go on that trail. Since that crash, I only ride with my Fox moto DOT when the speed is going to be high. 

Fast forward to this past weekend at a little ski area in AZ called Sunrise. I was wearing my "new" orange POC since it's not really a fast trail sort of place. I really like the POC because it's so light and airy, and so much cooler than a DOT for the AZ temps. This crash, I wasn't going that fast at all but went head-first after a failed launch from a log drop into a turn (the log drop just before the ladders on Chutes and Ladders trail for those who've been there). I crumpled upon impact (again to the right temple and shoulder) and saw this huge flash of light. I figured I'd broken my neck or back - the pain was that bad. But alas, I got up and appear to be fully functional (but quite sore). 

As much as I love my cool breezy POC, I'm thinking that this multi-crash EPP lid is just not protecting me like a FF helmet should. In other words, my own experience at having too many close calls with a POC helmet supports the OP's suggestion that an EPP helmet is not as protective as an EPS helmet.


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## rugbyred (Aug 31, 2006)

jurichar,

Not going to weigh in on which helmet is better as I have no clue.
What I am going to suggest, is wearing a mouth guard. 
I have played rugby for 20 years, been very fortunate to only had two or three concussions in my life (doctors would disagree and say I have had more)!
I went to Whistler this summer and decided to bring it as I figured I would be trying some silly things and wanted a little more protection for my head.
After trying it on the third day, I feel naked now when riding without it. There is no noticeable difference in breathing, and I now know if I have a spill and hit my head, the mouth guard is there to provide a little extra help for the brain if the hit comes from the right angle.

Eric


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## jurichar (Aug 19, 2009)

i've always thought about running a mouth guard. I do stupid stuff with my tongue sometimes. you dont see alot of guys wearing them though.


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## cerebroside (Jun 25, 2011)

There was an article in Motorcyclist magazine back in 2005 which is relevant to this, called 'Motorcycle Helmet Performance: Blowing the Lid Off'.

IIRC, the gist of the article was that (among other things) the multiple impact protection requirement of the Snell 2005 helmet rating meant that in most accidents more force was transferred to the wearers head than with helmets which only met the DOT safety requirements.

Looks like the original article has been pulled, but you can find it reproduced here: Article


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## billybobzia (Jan 10, 2004)

I don't know much about helmets I admit... I crashed rather hard this weekend, got my bell rung a bit, but just fine.. I wear a 661 DOT helmet.. how many impacts are DOT helmets capable of.. I got it because I know I am going to crash and want the best for my head...

Heal up broken folks, spend some time on the couch this summer and feel your pain...

Been thinking about the mouth guard thing tooo..


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## bullcrew (Jan 2, 2005)

Got a d3 the other day liked the urge but as hard as i hit in it I want a little more cushion for the push in. Lol


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## SHIVER ME TIMBERS (Jan 12, 2004)

bullcrew said:


> Got a d3 the other day liked the urge but as hard as i hit in it I want a little more cushion for the push in. Lol


to match your girlfriend the other night....ewwww...you need to cut back on the alcohol


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## naya the dingo (Aug 26, 2010)

SHIVER ME TIMBERS said:


> to match your girlfriend the other night....ewwww...you need to cut back on the alcohol


Damn it, some things just can't be unseen!


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## gticlay (Dec 13, 2007)

jurichar said:


> So in an optimal situation, in a crash you want your helmet to absorb/dissipate as much kinetic energy as possible upon impact. According to the law of conservation of energy, the energy dissipated has to go "somewhere." In the case of a single impact helmet the energy goes into the EPS foam which causes it some degree of stress and structural breakdown proportinally relative to the amount of force applied. In a multi impact helmet where does the force go? My understanding is that the materials have a rubber like property that allow the structure to reform or bounce back, but that energy is still contained within the helmet environment, and therefore transferred to the body in a higher percentage than if it were dissipated through helmet destruction.


Your flaw here is that you assume the energy must be transferred somewhere and not stored or converted. Much like a shock absorber, the energy can be used in the damping and that turns the energy into heat, or simply held for a time and released slowly (when the damping material returns to it's original shape. The energy is conserved, and not transferred to your brain box and it's either turned into heat or used returning back to shape, or some combination of both.


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## mtg7aa (Jul 11, 2008)

Thread revival time....

Has anybody seen any actual test results to effectively compare an EPS liner to EPP with as few other variables as possible?

The concerns in this thread are very valid, but there's a huge lack of data to make an educated decision.


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## HungarianBarbarian (Jul 24, 2008)

jurichar said:


> i've always thought about running a mouth guard. I do stupid stuff with my tongue sometimes. you dont see alot of guys wearing them though.


Using a properly fitted mouth guard can reduce the severity of a concussion. There is a lot of bad information out there on this subject many experts claim that mouth guards do not prevent concussions because no published evidence exists to show that. The logic behind this statement is false as is the statement itself.

The impact of face shield use on concussions in ice hockey: a multivariate analysis.


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