Dropped helmet: Throw out, or risk?

[vifferman]

Seems to be a lot of opinion, a lot of adhering to scare stories propagated by certain helmet manufacturers, but not a lot of fact.
Mind you, you did ask for opinions.

I've heard people talk about never risking it, for various reasons, but I'm pretty sure the outer plastic shell isn't damaged, and theres no reason for the foam/polystyrene inner layer to have been compressed.

I agree. Thermoplastic resin helmets tend to shrug this kind of impact off very well, unlike fibreglass or mixed-fibre RP shells. It's the way they're designed.
Fibre-reinforced plastics are generally designed to absorb the impact to a certain extent (without disintegrating) with the shell, then residual impact with the polysyrene liner, and the rest with the soft 'comfort' liner.
When thermoplastic shelled helmets were first introduced in the 70s (anyone remember the Polstar?), there was a lot of controversy about the fact that compared to fibreglass shells, they tended to remain intact on impact, so absorbed less of the initial impact. I'm sure some of this negativity was from companies who produced fibreglass helmets and were economically threatened by the cheaper and less vulnerable (to knocks and drops) injection-moulded newcomers.

Bonez, your helmet should be fine, but if you want total piece of mind, just replace it to remove any nagging doubts you may have. As others have said, it's only $200.

[Dr Bob]

Ditto, I will always buy plastic. Being a commuter and more likely to be storing my helmet on the floor of my office, in the spare room or in a cupboard I know it will be subjected to the odd small knock. I am not a plastics engineer but I believe that the thermo formed shell will probably not get any deep cracks or major loss of strength. Plastic is cheaper and more robust, but can tend to be heavier and not work as well. The only thing that will cause significant damage is if you repeatedly tap it with a piece of metal across its whole surface

[bear]

But isn't that like driving a 1970 Holden or a 2004 Holden, where if an impact were to occur the equipment would take more of the impact, and you would take less.

Dr Bob, do you have a fibreglass type helmet for weekend or longer rides?

[Dr Bob]

But isn't that like driving a 1970 Holden or a 2004 Holden, where if an impact were to occur the equipment would take more of the impact, and you would take less.

Dr Bob, do you have a fibreglass type helmet for weekend or longer rides?

Unfortuately I no longer get to do this, we have a car. Can't fit the kid and the missus on the bike.

[bear]

Unfortuately I no longer get to do this, we have a car. Can't fit the kid and the missus on the bike.

There is always the side car option - but then I guess you can't really call that a motorcycle can you.

[beanz]

Thanks firestormer, you seem to be the first person who's actually rationally thought about it.

I completely agree with the "being totally cautious about helmets and heads, and brain damage, etc", but theres gotta be a point where you stop and think about whats going on with the internals of a helmet, and how a drop will actually affect its shock absorbing qualities.

I mean, what if you drop it from 10cm? 15cm? 20cm? Surely you won't throw it away from a 10cm drop, so where do you cut it? No-one would reuse a helmet after it had been dropped from a 10 story building (regardless of "tests"), but noone would throw one out after they dropped it from 10cm. Theres gotta be somewhere in between where the drop actually permanently changes the helmet, so it won't absorb impact aswell. Thats what I'm trying to figure out... has my drop affected the helmet.

I just don't have a spare $200-$400 to spend on a new helmet, when my current one is possibly as-good-as-new. If we go around blindly replacing every "risky" aspect of motorcycle riding, won't we be actually riding 2ton bikes with rollcages, big springs facing every direction, and wearing a middle-ages suit of armour?.... or drive a car.

Also, thinking about the technical aspect of a typical head hitting the tarmac, the biggest forces to be absorbed are probably going to be to either side of your head. Thats probably where helmet designers design the most absorption to be. So, maybe a knock to the top of a helmet might not be all that serious.

OK, so it probably sounds like I'm trying to justify a decision to save money and keep the helmet. I tend to do that. But until someone can convince me of a technical reason why the drop would have affected the helmet, I think based on my current analysis of the situation, I'll add a wee bit more risk to an already very risky activity, and keep using it.

But hey, I'm always thirsty for knowledge. Does anyone know of a website which explains the technical aspects of a helmets force-absorbing system?

[Stinger]

I think your helmet would get more damage from being in the sun for a few hours than from a small drop. I doubt there would be any significant change in it.

[almonster]

Personally I don't think it would make a difference to the impact absorption. If it was me I wouldn't worry. I have seen some experimental tests on the net somewhere of this guy that dropped helmets from a 2 story building and then crash tested them against brand new ones. The results were that there was no distinguishable difference in impact absorption from the dropped ones to the brand new ones.

If the helmet was screwed after a 1m or so drop I wouldn't want to wear it in a 100kph+ bin.

But its your head and you decide what you want to do with it. I wouldn't worry.

im with you on this one if you come off at speed you want it to take more than one hit

[Menial]

fuck, I wouldnt trust my head In one of those helmets at the best of times.

[Redstar]

This is what you must do..submit your helmet to the DSIR helmet testing department, you will find them in the Yelllow pages under ''testing division" they certify helmets to NZ1894 CE 12 accreditation, It will only cost $30 Cheaper than a new helmet even at $200. First they will carry out an ultrasonic Xray test this will show any errant hairline fractures. next they will stress test the shell using a compression tester, next an ultraviolet infra scan this checks for exteria delamination fibrosis.(fishures that might later cause problems. and finally to make sure you are safe the helmet is placed in a sim. Jig dummy head and a steel bolt is fired from 1 m at a force of 600kg point impact ( you can wear the helmet with confidence after this test)
Ps I made this crap up! i do that a lot....

[beanz]

From what I've found out about helmets, they usually consist of an outer plastic or composite shell, glued to a 20mm layer of suitable density polystyrene, covered in some foam padding inside for comfort. Some of the more expensive helmets might be different, but essentially thats all there is to them... nothing too tricky.

The polystyrene layer is designed to compress around the point of impact in a crash, to absorb the forces. This is an irreversible action; the polystyrene can only compress once.

When I dropped it, and the outer plastic shell at the dome of the helmet hit the ground, the plastic would have been deflected inwards a bit. I guess about 1-3mm, as compared to the impacts it would need to be designed for, this was a tiny one. The inner polystyrene layer would subsequently have been compressed 1-3mm too, in that local area. The plastic shell then would've bounced back to its original shape, but the polystyrene would probably stay compressed and become locally delaminated from the shell.

So, the drop would probably have reduced the maximum atainable impact absorption by a small amount, but I believe this is negligable.

I also believe the polystyrene has partly or fully expanded back to its original dimensions, because I tried the "tapping test" (explained in someone elses post), and the tapping was exactly the same note all over the surface of the helmet, indicated no hollow area where the polystyrene was compressed or a different density.

All materials have an "elastic" region at the start of their deformation where they bouce back to their original dimensions, eg bending a piece of metal, squeezing a solid rubber ball, or in this case squeezing a block of polystyrene. I think the drop I gave the helmet only deformed the polystyrene inside its "elastic region" and wasn't enough to permanently deform it.

Cheers for all your opinions guys. :-)

[Drunken Monkey]

Mine got hit by a one-bounce-four cricket ball today. Couldn't even see the (cherry) mark. I'm not going to replace it. It'll be mint, bro...er...I think...

[Fordy]

RiDE magazine, affectionately nicknamed DiRE, did a series of tests in issue 96, April 2003.

The test:
HJC ZF8 helmets, dropped from 1m, 2m and 3m onto a concrete slab and one out of the box for a control.

The results:
All helmets passed the European test (IMHO the graphs for them all were practically indistinguishable, ie the drop did not appear to affect performance).

Conclusion:
Our industry experts are right to err on the side of caution. Even though our graphs show this particular model of HJC helmet absorbed enough impact to still pass ECE 22:05 even after dropping it from three metres, it doesn't mean you can be careless with your helmet. You need to use a bit of common sense. Other impacts, even smaller impacts than our one metre drop test could cause invisible fractures that may cause your helmet to under perform in an accident. If you drop your helmet and you're even slightly worried you may have done it some damage, buy a new one.

Obviously they're jouno's and not scientists and they want to sell magazines and not rigorously test their theory. Make of that what you will.

[avgas]

i dont trust $200 helmets in the first place, so if it had been dropped i really wouldnt trust it

[inlinefour]

i dont trust $200 helmets in the first place, so if it had been dropped i really wouldnt trust it

But at the end of the day its not my head, and by the sounds of all this people will do whatever they wanted even after asking for opinions. I go and purchase a new helmet, but I'm fortunate enough to be able to afford it