I'm going to assume your asking why Fire Helmets are longer in the back? It is designed to keep hot liquids from running down your neck or back.
If your asking about the nomex that comes down around the neck and ears it is to protect the neck an ears from the heat. Hope that helps.
I have seen many European departments with the helmets with no brims. But, some of them also have hoods that cover the helmets in a fire. We do not cover our helmets and need to deflect hot items from entering our coats, like the Chief stated.
yesterday, someone ask to me. Why, back of fire helmet (usa) have designed long side. I no want wrong answer to him. So i ask you all to explain to me about that asking.