why the five year life span on helmets?

[boatdetective]

So, I'm interested to hear technically why there is an arbitrary recommendation to replace helmets every five years. I don't want to hear "because the manufacturers say so", or "because in that span it most likely rolled off the table once or twice".  I want some justification that shows that the expanded foam liner somehow degrades. I just don't buy it.

Personally, I'll probably want a new lid purely out of vanity. However, I don't see where there is a hard engineering reason to toss the old one.

[Triple Jim]

I view it as a CYA specification, and will replace my helmet when I believe it has degraded enough to increase my risk of injury.   I realize this invites opposing view posts, and that's OK.   

[oldbike54]

 Read somewhere it has to do with degradation of the shell .

  Dusty

[Arizona Wayne]

It's probably because if you don't wear a headskin to keep your body oils out of the soft foam, that foam will disentigrate.   Or the same logic to convince you to never keep a tire longer than 5 years no matter how it's treated.    Whatever you decide to do, you have been warned.  That way the manufacturers are not liable.

[JoeW]

From what I remember it's the natural fatigue of the material. Fiberglass as it was explained to me, shrinks over time and looses it's elasticity. I don't know about modern composite or plastic helmets. This is what I remember from 30years ago. I find that after 5or 6 years, my helmets don't fit as well as they once did. Looser and more comfortable but, I do know that a loose helmet does not protect your head as well.
http://www.bing.com/search?q=why%20do%20we%20need%20to%20replace%20motorcycle%20helmets&qs=n&form=QBRE&pq=why%20do%20we%20need%20to%20replace%20motorcycle%20helmets&sc=0-0&sp=-1&sk=&cvid=A9C6CFCAE6D3427A974DBC7B6330F305
I'm working from my stupid tablet so cut and paste doesn't work that well. But, here's some information

[LowRyter]

a good excuse to sell more helmets?

[Triple Jim]

I feel better, now that I'm not alone.       I would be very surprised if decent glass/epoxy or glass/polyester or molded polycarbonate shell degraded significantly after five years, especially considering the outer layer of pigment that probably blocks most/all UV.  Maybe there's something to be said for the sweat attacking foam theory, but I've used bicycle helmets with polystyrene foam for many years with no degradation that I can feel.  The expiration date is almost certainly like the one my wife noticed this evening...   ... on dental floss!

[Guzzistajohn]

i probably wear mine too long. I like to buy helmets when there's a close out sale. Last years model is ok with me.

[boatdetective]

I work daily with fiberglass and the resin most certainly does not embrittle with time. Older GP polyester resin technically would "shrink" due to cross linking over time. However, this would not change the properties. The "body oils" attacking foam makes no sense to me either. More and more, I think this is a figure determined by defense attorneys rather than scientists.

[pikipiki]

The plastic shell will definitely degrade over time due to exposure to sunlight. Newer helmets ma resist this a little better than older Ones. Grease oil solvents also effect plastic. If manufacturers say 5 years, your not in the saddle all day everyday and keep your helmet in a dark cupboard it would be reasonable to keep a helmet considerably longer.
One curious fact about biodegradation of plastics is that the color effects life so if I get this the right way around, a red helmet should in theory outlast a yellow one.

[cookiemech]

I recall that one of the motorcycle magazines (could it have been Motorcycle Consumer News) did an article a few years back where they took some of their old (in some cases VERY old) helmets and subjected them to impact testing, to simulate the tests run on new helmets. Their conclusion was that unless the helmet was subjected to impacts (like falling off the bike or being routinely stored atop a sissy bar) or subjected to chemical attack (probably for the polycarbonate helmets), they really didn't degrade significantly.

[kingoffleece]

I'd suspect a larger part of the 5 years, which is from use, and 7 years from date of manufacture no matter what, has to due with liability.

I'd wager dollars to donuts that a OEM will walk away from any claim and cite the timeframe as the reason.  This would have to be backed up by some kind of "evidence" that the time frame is valid.

[Chuck in Indiana]

Polycarbonate *is* attacked by hydrocarbons. How much and over what time period needed to degrade a helmet is open to conjecture. Fiberglass and carbon fiber are attacked by heat/sunlight. There is a reason that plastic airplanes are *required* to be white because of this. Friends don't let friends fly plastic airplanes.. especially if they've been tied down outside for any length of time.
 

[Kev m]

Isn't the concern about the impact absorbing liner, that it hardens either due to exposure and/or use? If it becomes packed down/more dense it transmits more force in a crash.

I wouldn't compare bicycle helmets because possible impact forces should be dramatically lower.

That said, I kept my last, rarely worn FF Arai something like 15 years.

[Rough Edge racing]

 Millions of big trucks with fiberglass tilt hood/fenders pounding the highway and all the Corvettes haven't vaporized  Older Vettes usually developed a lot of cracks after maybe 10 years...But vehicles are subject to a lot more vibration and shock while in use than a helmet...
 As mentioned, how the helmet is stored will affect it's life....

[Dukedesmo]

Consider the amount of use a helmet gets over five years.

Some are worn for several hours everyday in all weathers, others are worn for a couple of hours at the weekend during summer months, so the 5 year thing is completely arbitrary IMO.

AFAIK the biggest deteriorator is UV light so those exposed to the most must surely deteriorate quicker? as such I'm happy to leave mine longer because I fall more into the sunny weekend user than everyday commuter. Other than for damage I generally replace mine when the interior starts wearing out...

[Two Checks]

Replace your Corvette every five years. That goes for boat hulls, too.

[Chuck in Indiana]

Replace your Corvette every five years. That goes for boat hulls, too.

Apples and Oranges..

[boatdetective]

Replace your Corvette every five years. That goes for boat hulls, too.

Man, GM and the Marine Industry would give you a big sloppy French kiss if there was any truth behind that.
In practice, the resins used in a laminate are not exposed to UV, as the finish is generally painted or gelcoated. Epoxy resin will get attacked by UV. UV will have an effect on (I believe) thermoformed plastics. However, I'm not so sure about cross linked, thermoset plastics. There are 45-50 year old fiberglass boats out there, and the last thing that is gone is the hull.

[Kev m]

Isn't the concern about the impact absorbing liner, that it hardens either due to exposure and/or use? If it becomes packed down/more dense it transmits more force in a crash.

I wouldn't compare bicycle helmets because possible impact forces should be dramatically lower.

That said, I kept my last, rarely worn FF Arai something like 15 years.

As I thought. You guys keep talking about the shell, but it sounds like it's the liner:
http://www.smf.org/helmetfaq#aWhyReplace

But they also admit it's a loose standard/judgement call:

The five-year replacement recommendation is based on a consensus by both helmet manufacturers and the Snell Foundation. Glues, resins and other materials used in helmet production can affect liner materials. Hair oils, body fluids and cosmetics, as well as normal "wear and tear" all contribute to helmet degradation. Petroleum based products present in cleaners, paints, fuels and other commonly encountered materials may also degrade materials used in many helmets possibly degrading performance. Additionally, experience indicates there will be a noticeable improvement in the protective characteristic of helmets over a five-year period due to advances in materials, designs, production methods and the standards. Thus, the recommendation for five-year helmet replacement is a judgment call stemming from a prudent safety philosophy.

[Cam3512]

For the same reason ballistic vest manufacturers put a 5 years expiration on their product.  To sell more.  Due to perceived liability they get replaced.  I've shot vests that were 20+ years old and it still worked.

Expiration date on life protecting gear = $$$

[jackson]

Strictly $$$$$$$$$ driven.  As long as the liner & padding have not deteriorated, there's no reason to trash a helmet; especially at the prices that are presently being charged for quality helmets.

[charlie b]

I agree that it is not the shell.  Even if UV would degrade the basic shell material, it has a protective coating, gelcoat or similar, that would take the brunt of the UV.

I also agree that the issue is the foam liner.  Not the comfort foam, but, the beaded foam.  That stuff does degrade over time, but, does it degrade enough to affect the performance?  I think not, but, it depends on use and storage.  How hot does it get in storage.  How many oily products you use on your hair, how often it is cleaned and what it is cleaned with, etc, etc.

I can see why the mfgs have chosen a time limit, based on the most horrid of circumstances.

Having said all that I still replace my helmets after 5-7yrs.  Mainly cause I want a new one, not becasue I fear for my safety :)

[Two Checks]

Apples and Oranges..

NOT apples and oranges. People aresaying fiberglass deteriorates over time. If tha was true, my statement would be correct.
And GM and boat makers would be ecstatic.

[Stevex]

Took this directly from the UK Arai site as my RX-7 Corsair is now 8 years old and I wanted to know when I should start looking for a replacement.

Arai helmets are handmade to the highest possible standard, and although after many years the outside shell can look as good as new, it�s the EPS polystyrene liner that loses its ability to absorb impact over time. Arai recommend replacing your helmet 7 years after date of manufacture and 5 years after date of purchase to maintain the maximum levels of protection.The EPS liner is effectively the shock absorber of your helmet, absorbing the force of an impact onto the shell. This is done by the cells in the poly styrene being expanded (EPS = Expanded Polystyrene) and filled with air to absorb impacts. Over time, even when not in use, these liners lose their air pockets incrementally, after 7 years, dropping the shock absorbing ability of the liner below Arai�s safety standards. This is why we declare the helmet due for replacement so it can properly protect you against impacts.

[Chuck in Indiana]

NOT apples and oranges. People aresaying fiberglass deteriorates over time. If tha was true, my statement would be correct.
And GM and boat makers would be ecstatic.

If you helmet was as over designed as a boat hull, it would be too heavy to wear. <shrug>

[Aaron D.]

This summer I took a sledgehammer to my 18 year old helmet. I would not worry about shell degradation. Frankly I doubt much was wrong with the liner, which eventually came out.

My boat is fiberglass and 41 years old. Not worried.

Bicycle and ski helmets are pretty much all liner. But oddly according to at least one study neither makes a significant difference in the prevention of serious head injury..

So I use the Smell 2015 test. If it smells bad this year I replace it.

[segesta]

Although I replace my helmet every few years, it's obviously better to wear an old one than none at all.
As in, I don't think any obituaries read "He was wearing a helmet, but it failed due to sunlight degradation of the plastic, and this is the sole reason for his death."

[Kev m]

Here's my take.

Recommendations like these (and there are hundreds of them from helmet replacement to kids car seat replacement, or keeping kids turned rear facing till they are THREE etc., maybe even ballistic vests too) are all probably based on good SCIENCE.

They are probably determined for worst case scenario to MAKE SURE to absolutely minimize risk to life and limb.

Most of us who stretch these recommendations probably have some anecdotal story why we found it conservative, unnecessary etc. But our limited anecdotes obviously don't address the worst case scenarios.

What we can't really quantify is the important question of how much the risk changes. Does the risk of death or injury in any one given scenario change 1% or 10% or 50% if we ignore them?

Hell, they are already safety devices which are designed to be in place JUST in case but are pretty rarely used by any one of us in the first place.

So that's the question you have to ask yourself. How likely am I to need it and how likely am I to suffer from the potential degradation of the materials.

We can't do anything but take a guess and hope we didn't miss something in our risk assessment.

It's the same thing when we discuss oil types and change intervals.

So do what makes you feel warm and fuzzy.

I'd rather have a 15 Arai then no helmet at all. But then again, my new Arai I finally bought last year is clean and comfy. I'm glad I finally broke down and got a new one. Same goes for my new Shark 3/4.

[Triple Jim]

I wouldn't compare bicycle helmets because possible impact forces should be dramatically lower.

Some reasons that might not be a good generalization:

1. Bicycle helmets have a lot of ventilation spaces, so the pressure (psi) on the materials for a given impact is higher than for motorcycle helmets.
2. While average riding speeds are lower for bicycles, downhill speeds can easily get over 40 mph.
3. With some accidents, the speed that the 2-wheeled vehicle is going may not matter as much as the speed the car that hit it was going.
4. Many motorcycle helmet impacts result from the rider's head hitting the pavement, when it's able to slide, rather than be stopped by something like a curb, so the impact in those cases is mainly a fall from six feet up.