5:07 p.m. on August 2, 2010 (EDT)
I am not saying that just because a bear is within 30ft or so or it is close but you have an obstructed view because of trees or whatever to start spraying. The effective max range of the sprays is 25-30 ft. Just because you come around a bend in the trail and are stareing a bear in the face doesn't mean you should start spraying.
Bear spray should be a last resort when you feel you are in imminent danger, when the animal is charging/attacking you. You need to understand a little bit about bear behavior before you employ your "weapon" whatever it may be. For example black bears are known to bluff charge.
Just because you are close to a bear but have an obstructed view of him doesnt mean to start spraying the trees. If and when you feel you are in imminent danger then you aim at your target, aiming at a head half blocked by a bush/tree wont do you much good. If this means that you have to wait until the animal is basically on top of you, then that's what you wait for. If you don't at least have a somewhat clear shot, then you are wasting your only defensive device at that point. "Don't fire until you can see the whites of their eyes!"-Battle of Bunker Hill
Lots of things should be used before your last resort (bear spray), such as giving the animal space by slowly backing away, making noise, lights at nighttime etc.
If you feel that just because you have seen a bear that you need to start spraying you are very wrong, and will likely become a chew toy at some point in your life.
Bears are creatures that demand a high level of respect, and as long as you give it to them in all of your actions from food storage to actual encounters. Then you will probally never have an issue. But should you, for whatever reason find yourself in that situation that is life or death, then by all means pop off the safety and spray away.
I worked in law enforcement for a number of years, and dealing with bears and suspects is pretty similar. You exhaust all of your options first, before you use your weapon. You can make noise, you can back away, you can use proper food storage and handling techniques etc. If all of the other methods fail and the animal you feel is about to attack then draw your weapon and give it two in the chest and one in the head. In law enforcement we have to exhaust all of our non lethal force options before using our firearm, sometimes this means you try every single one first, othertimes you have no choice but to immediately employ your weapon.
The chances are that if you come face to face with a bear that it will not attack. Bear attacks happen, but are uncommon. Most encounters end peacefully with either you leaving the area or the bear leaving the area. I have had quite a few bear encounters in my time in the back county, and all of them have ended peacefully. I would say about 75% of the time the bear once they realize you are there, or shortly after noticing you will run off. Sometimes they don't and they hold their ground, that is when you should back away slowly. A mother and her cubs can be a different story, give them plenty of space.
Lastly, i was exagerating with the 100mph comment. Yes, any spray can blow back at you. But if you realisticaly think about the situation where you would be forced to use a bear spray, then that is an acceptable risk. Because it is used to prevent or stop an attack. If you gonna be attacked you may as well try to save yourself yes? Spray like a wildman, aim for the bears face, and if you happen to catch a little in your face, it will be much much less than the bear recieved. Take your chances. Turn your head away and close your eyes if you can, or maybe use your forearm to block some of the blowback from hitting you squarely in the face.
Life or death situation, best case scenario you hit the bear and stop the attack and can escape from the situation, and you don't get hit by any of the spray. Worst case scenario you get mauled and eaten by a bear while your eyes and face are on fire, but hey by the way you were already gonna be mauled and eaten, remember? And anything else will fall in the middle somewhere, better off trying than not IMHO.
Sorry for the long rambling post.