Originally Posted by
dougmc
Yes, it took some energy to compress it to the point that it would split, and then some more to actually split, and that's energy that didn't go into splitting your head. The question is if this is a significant amount of energy, and I don't recall ever seeing anybody actually measuring this.
Yes, if the helmet split, it failed. But the assertion that it provided no protection up until that point is unsupported as far as I know. Common sense (or simply my own educated guess, take your pick) tells me that it probably provided a little protection up until that point -- but not very much -- but I have no evidence of this either way. Do you?
It wouldn't be a difficult thing to test -- get some sensor-laden crash test dummies, and throw them around (in a controlled and repeatable way, of course) in such a way that their heads have harder impacts than bicycle helmets are designed to protect against. Repeat with and without helmet, at varying impact levels. Keep track of the condition of the helmet after each impact, as well as the sensor readings and the intensity and other details of the impact.
Common sense suggests to me that this is correct (simply due to the trend of adding more and more ventilation), but do you have any citations or other data to back this up?
well, that's a problem now, isn't it?
Manufacturers keep a close eye on this but don't want to give out information on it as it can reflect badly on the protective qualities of their product. Certainly we know it happens and manufacturers try to prevent it, but fail to do so. Letting people believe broken helmets are helmets that have "worked" works in their favor. Telling them that when a helmet splits, cracks, or comes apart the helmet isn't useful doesn't help them at all.
I've had a Bell representative tell me that a helmet splitting is a valid form of attenuating energy, which of course is technically true, but misleading in the extreme. Helmets work via compression, not by splitting.
Measurement rates of energy that coincides with the splitting of helmets is also extremely difficult to come by but we know at what rate of impact a helmet is tested to and that rate does not correspond to real life serious injury or death situations. Most conditions that result in such serious results are far beyond the limitations of helmets. Manufacturers are careful to say their product cannot be relied upon to prevent these types of injuries and that serious injury can occur to any wearer of their products by any impact.
Collisions, falls, and impacts to the head is an extremely complicated issue and not one that will be controlled by a single, simple, mitigating factor. Despite what emotion Helmeteers bring to the table, placing a helmet on a head does little to change much.