I had a cat strangled by her collar to the point where she passed out. This WAS a safety collar that is supposed to release. Had I not been there to remove the collar (could not do this till she past out as I couldn't get hold of her) then I am sure she would have met a tragic end.

I know of other stories of simular things happening. A cats protection lady told me of a cat that was found hanged by her collar. Awful story!