The liner of the helmet is a very functional component and is designed to absorb and disperse an impact so it's not all directly transmitted to your skull. The shell will absorb a certain amount and this is the reason that it's not necessarily a bad thing to crack a helmet in a crash.
The liner is often made from expanded polystyrene, which is liked those white-colored packing material inside new TV or DVD sets in stores, acting against shocks too during the delivery. It works the same to the head too. However, different manufacturing techniques are used by different companies to get the greatest possible dispersion of impact forces. Helmets meeting the minimum federal safety standard (DOT) have 1-inch thick inner liner of appropriate firm polystyrene foam. Always, the inner liner is not visible. Unsafe helmets normally contain only soft foam padding or a bare plastic shell with no foam at all.
The density of this liner can not be too soft or too hard. DOT & ECE requires thicker liner than SNELL somehow. If you crash and hit your head the outer shell may look fine but the liner may have had to absorb the impact and by doing so the polystyrene may have been greatly compressed.
If there is a subsequent impact the liner will not be able to absorb or compress to the same degree and if the polystyrene is completely compressed it will offer no benefit and the forces will be transferred to the rider's head which may result in serious concussion.
No comments:
Post a Comment