In reply to Wayne S:
I like squeeze chimneys, as there is virtually no way of falling out of them. You can always jam feet to knees, knees to arse, belly only, chest only, chest and shoulders, head jams if necessary, ....
I am rather heavily built (179cm, 100kg) , so I often need to resort to that style while my partners are still chimneying normally.
Solid offwidth technique also helps against the fear of getting stuck. Once a chimney gets too narrow for udging and grunting you can usually move towards the face (not fully out) and use heel/toe jams, chicken wings, arm and shoulder bars to get around the constriction.
Usually the main obstacle is the harness, though, not the helmet. I have climbed one chimney here in Saxony where I took off my harness, and tied the rope to my leg instead and hauled the harness and gear up before belaying my second. As I said, you can´t fall out of a full body jam anyway.
CB