As for spray not asphyxiating the bear, go back and reread Shelton's books, he thinks it does.
I don't recall anything in shelton's books saying the spray asphyxiates the bear. At best it might make breathing painful.
And in all the hundreds of cases, there's not one case of the bear 'dropping' as you suggest, they all turn tail and run.
Further - if the way it worked was to choke off air supply (asphyxiation) you'd be dead every time - a bear can go without oxygen for quite a while before dropping, certanly long enough to get the 'job' done on someone he's charging.
And further still - we know it doesn't work like that on humans at all. Police don't use it because it causes the person to drop due to any sort of lack of oxygen.
This is essentially concentrated cayenne pepper. It does the same thing to you as if you ate a very very hot pepper - it causes intense pain and causes the mucus membranes to water agressively. On a bear that affects their sense of smell and their vision (hard to see when your eyes' are burning and watering, and it's also harder to smell). It also causes intense pain. This causes the bear to break off and figure out what the hell is going on and makes it harder for the bear to figure out where you are and what threats are in the area. It doesn't even know why it hurts, and its' probably never hurt quite like that before. That is why it works. It doesn't actually physically disable the bear at all. It isn't a neurotoxin or anything that would affect neurological functions in the eye or lung.
At no time will the bear be in any danger of passing out!
Perhaps my pal had a allergic reaction to the spray, beats me, but he still has an eye problem.
Well that's entirely possible - you can kill someone with a peanut if they're allergic after all and that effect can take days to wear off without medical treatment for the allergic reaction.
But i must say that's very rare, and it's not hard to test before you carry spray. Anyone who's allergic to capsicum of course should not consider this type of defense, it could easily be very dangerous to them even if it were to go off by accident.
When a bear immediatrely turns 180 degrees from a committed attack, that is an indication that something has happened to it.
I have to tell you - that is not true in many cases for black or grizzly bears. I know this from both personal experience and numerous documented incidents. If the bear is any kind of distance from you that can very easily be true, but close in i've seen a bear slinky and twist like it had been slapped in the face with a bat and swap ends and run like the demons of hell were chasing it. That would have been about 15 - 20 yards. There are also several stories of bears attacking someone and being driven off by another person with a gun firing into the air because they couldn't fire at the bear without risking hitting the person - the bears in those cases also took off at warp 10. There is another well documented case of a ranger firing his pistol at a charging griz and having it swap ends and blast off, he THOUGH he must have hit it, but the bear was tranquilized and found not to have a single mark on it. (rather embarrassing for him, it was near 'point blank' range.)
My guess is the range the bear is plays a large role. I would guess that being closer to the muzzle blast would make it more likely for an animal to be 'scared' off by it. Just a theory but obviously it makes sense that the blast from a gun a 100 yards is less than it would be at 50 yards and less than it would be at 20 yards or 10. That bear looked pretty close to them when he fired.
But if he says he missed, he probably missed.
Maybe polar bears are just hard of hearing.
I have no idea! - that would be interesting to know. Certainly they have different temperments. It would be interesting to find out, not that i'm likely to run into a polar bear
It's possible something else about their physiology makes them less affected by the blast. Polar bears really aren't something i've spent much time looking at.