Hey Mark,
I do not think that these boys had bad gas disipline, I think that theywere in an area where gas was not commonly used, on the coast it would be unlikely to use it due to weather and wind conditions, not to mention that ther would be a less concentration of enemy (even though tere would be the same number of men in the trenches, the fact that the trenches ended abruptly at the coast would make it a waste of resources to have the gas attack go out over open water)
As far as the use of chin straps go, I have been told by vets that they were told not to use their chin straps during battle, as the concussion of an explosion would tear their head off if the strap was hooked, this makes no sence to me. I would suspect that some where a soldier was observed decapitated with little other damage, and it was assumed that his helmet pulled his head off, if you check WWII period photos, you will see that many GIs would have their chin straps hanging (not to confuse the strap that is over the visor, that is the chinstrap of the helmet liner and is always worn over the visor to keep the two parts together)
Gus