Regardless of the approval process a helmet that does not fit you well will not offer the package of protection to prevent head injuries that you are buying the helmet for in the first place.
It is essential that you choose a helmet that fits your head.
Many manufacturers offer helmets in sizes such as small, medium and large, with pre-fit liners. The best way to buy a helmet is to choose one that allows you to purchase the liner separately from the shell.
This way you can get a better fit. The Snell Foundation suggests that you wear helmet for a couple of hours, just as you would an expensive pair of shoes, to make sure it is comfortable on your head and that there are no hot spots.
It is important that you properly tighten the chin strap so the helmet will remain in place in the event of an accident.
When you first put the helmet on, tighten the chin strap so it is slightly uncomfortable. Within a few minutes you will no longer notice this. Tightening the chin strap in this fashion will help keep the helmet in place which is why you are wearing the helmet in the first place.