The testing system used for helmets doesn't allow for helmets to sustain multiple impacts, it's not that the helmet necessarily failed to protect against a level of impact, it's just that it's a different design.
Yes, the Brock foam used in Bern hardhats is designed for multi-impact use instead of the single-impact EPS foam. And yes, the testing system is single-impact (not exactly sure of the specifics, but it involves strapping the helmet to a dummy and dropping it onto a hard surface once). But you are wrong when you say that "it's not that the helmet necessarily failed to protect against a level of impact". ASTM/CE standards simply describe a certain level of impact that helmets must fulfill at least once. Hardhats by definition fail to protect against this level of impact the first time
. If they could withstand the impact once, they could be marketed as "multi-impact helmets
" instead of this "hardhat" name, which would make it sell even better. As an example, Pro-Tec developed their own multi-impact SXP foam
that is certified ASTM/CE. Even with multi-impact capabilities, SXP foam is able to protect against the level of impact that ASTM/CE demands, which is something that the Bern hardhats cannot.
neither (and this goes for nearly all helmets with a few exceptions) are designed to prevent concussions and the like.
Yup, this is where it gets tricky...
Concussion damage research is still in its infancy, and there are no helmets in the universe that can claim with solid scientific backing that they can reduce risk of concussion. Not even NFL-level football helmets can be marketed in that way. The force of a fall is only one variable in determining whether you get a concussion or a coma, it also depends on the direction of the fall, anatomical differences between individuals, the amount of rotational forces in the fall, etcetc.
Now for the non-scientific part...
The way I see it, tokyo_dom has the right idea, but i'd probably (subjectively) put it like this:
Impact force: 1...2...3...4...5...6...7...8...9
Why? If you look at Bern hardhats, the layer of foam is pretty thin compared to some EPS helmets (hence the steezy look). This means that the Brock foam used in Bern hardhats is pretty badass in terms of deforming and rebounding since it provides much better cushioning for its thickness. However, it also means that Brock foam cannot protect against large impacts very well at all.
If Brock foam were only slightly worse than EPS in terms of single-impact protection, then all Bern would have to do was to make their helmet padding thicker and it would pass the ASTM/CE tests, and they could market it as the ultimate "multi-impact helmet". It would be darned comfortable, multi-impact, and
pass helmet certification - they would sell millions of those. The fact that they didn't do this means they couldn't get it to ASTM/CE certifications with a reasonable foam thickness.
I sound like i'm anti-hardhat, but i'm not - just wanted to correct some facts out there. Falling from a bike, for example, is unlikely to generate so much force to crack a hardhat or a helmet. Bike helmets are designed with commuters in mind, so the forces involved in low-speed collisions with cars are significantly higher. If you aren't doing anything too extreme, a hardhat will probably suit you fine!