Originally Posted by
cyccommute
You may know more about the use of your helmet but what do you know about the impact that use has on the polymer? The manufacturers have more knowledge about the material than you or I do. I (might) have more knowledge about the polymer than you do since it's my job to know about chemicals and chemical reactions as well as how materials change over time, i.e. "aging". My field isn't in expanded foam nor in manmade polymers but I do pick up knowledge about materials outside of my expertise from time to time for various reasons. All objects...manmade or natural...are subject to degradation through exposure to the environment. How that exposure influences those objects can be difficult to predict. A helmet that is 20 years may be perfectly fine or it could be severely compromised. Most of the compromisation is going to occur at corners and sharp edges of which helmets have a lot. Visual inspection won't tell you anything. Destructive testing might...depending on how you do the testing...but that's not going to leave you with a workable helmet.
The paper on helmet aging cited above indicates that helmet may age well but it has some flaws. We don't know the entire history of each helmet. They didn't test the helmet at the edges because it's too hard to sample there. The experiment doesn't have very good controls since the helmets are donated and don't have a specific history. Do all the helmets have UV coatings or additives to protect them? It would also be good to see a controlled, accelerated aging to see if it matches real world aging.
Perhaps it's all a conspiracy by Big Helmet or it may just be a CYA by Big Helmet to squash the little guy. Then again perhaps not. Do you have any information to address the above concerns or evidence that Big Helmet is doing something nefarious? Have you tested your helmet for degradation byproducts? Have you tested your helmet to see if it is holding up? Or do you look at it and say "seems okay to me" without any basis to say that?
As I've said above, my helmets seldom last 5 years before I biff them against the ground but, even if they did last 5 years, replacing them at that interval isn't that odious. It's cheap insurance and I can take advantage of new technologies.
Again, how do you know it "still works fine"? The only way to test it is to destructively test it. You can do that in a laboratory or you can do it by smashing it on the ground with your head in it. One way hurts a whole lot less than the other. In the end, you might have an answer but the helmet is no longer "fine". If the helmet isn't "fine" when you smash it into the ground with your head in it, it could have dire consequences. Either way, the helmet is going to end up in the landfill.
You have an argument that proves way too much--if inspection is essentially useless, then I have no way of knowing whether the helmet was fatally compromised in shipment or just basic handling at the store. Obviously, the only rational way to do this is to acquire a helmet right at the end of the production line after, of course, minutely observing every facet of the helmet's production.
Sorry, but if the CPSC says up to 10 years is ok, I'm finding it pretty damn hard to believe that the manufacturers have some secret knowledge that the CPSC doesn't regarding degradation over time.
Can we stop with the nonsense "conspiracy" condescension? These are all business concerns with marketing departments, I don't have to be some sort of paranoid to think that might affect their call on when replacement is needed.
BTW, I don't think anyone here is suggesting that someone use 20 year old helmets,. The question in the OP was specifically about 3-5 years. There seem to be plenty of sources more knowledgeable than thee or me that indicate that that range is not based on anything.