First up Gwendy if you have a health risk with the current helmets then no one should make you wear one, got me stuffed why anyone with a brain would make you or have you justify why you want to still ride, go figure. Also thanks for the heads up (

) re styrene. All types of plastics are a chemical cocktail of crap, I'll give you a big tip, never ever breath in the smoke from burning styrene.
Ok, nearly every day someone here in Cairns gets knock a$$ up off their bike, I've seen plenty of them and if you don't go under the wheels and have a helmet on, there is a very high chance you'll be ok. I've seen quite a few helmets in pieces (yep lots of them break apart) but the rider's head is fine. I believe if you are doodling around on proper bike paths, not the little crapy lane we have on the side of our roads, then maybe no need for a helmet.
Cheers Uncle Bob