Unfortunately, as per my agency's super bright, I too had to be sprayed with pepper spray in order to carry it on the job. Something about if I had to spray someone, I could articulate why I did so b/c in my experience.... Didn't make sense to me since in order to carry a gun I didn't have to get shot with it first. We were told that there is a small percentage of the population that pepper spray will not affect mainly darker eyes and skin pigments. However, once it makes it to the upper respiratory system, it should affect nearly everyone.
Anyhow, I have witnessed pepper spray not work on a guy who was high, on steroids and in a rage. He got the s@*% sprayed out of him too...
Not sure how well it works on bears.