A 1997 police study found that OC (pepper) spray successfully incapacitated subjects in 90% of studied incidents. A subsequent study in 2001 found no significant risk of asphyxiation due to pepper spray - so it is both reasonably effective and reasonably safe to use. However, many military personnel are expected and trained to fight off attackers when sprayed , and though difficult, they are almost all able to push through. Clearly, OC has its limitations.
there are a number of factors that might decrease the usefulness of your OC spray, and it is important to understand them
Sub-standard spray: Not all pepper sprays are created equal. Stick with well known, respected brands like Sabre Red, and Kimber. The ingredients in poorly made OC spray can separate, making it less effective. Aerosol propellants can also break down, decreasing effectiveness. Replace about every 2 years, and regularly shake the can to ensure a good mixture.
Strength: 10% OC is a good percentage. Be wary of lesser amounts.
Size /Range: Many mini sprays do not have the distance or the volume to be truly effective.
Use & dispersal: There are multiple types of delivery systems – foggers, streams, foam, gel, cones, etc. understand the benefits and drawbacks of the type you choose. This video shows the different types, and how to properly deploy them. Be careful deploying OC in confined spaces or in adverse weather. If you use pepper spray on someone, it is common to be partially affected yourself. If you have respiratory problems, pepper spray is probably not a good match for your personal protection consideration. Recognize that it will take a little time for the spray to set in, and that pepper spray may not fully incapacitate a dedicated attacker (no stopping power), just make them functionally blind for a while. use OC as an escape tool, not a fighting tool.
Training: Many brands offer inert versions containing aerosol but no OC for training. If you can, get and use these to practice deploying the OC and hitting a target. make sure you carry your OC in an accessable location - rooting around the bottom of a bag in a self-defense situation is not ideal.
Treatment: There are a few traditional treatments people use to flush their face (baby shampoo, Maalox, milk, etc) but according to this study , none of these options had any real effect. Just time. Some companies sell “decontamination wipes” for their brand of OC, but these weren’t included in the study - maybe they’re worth looking into. Also, apparently OC stays on the skin for a fairly long time, and you’ll feel it again if your pores open up, like they do in a hot shower. Don’t be alarmed when you “feel the burn” when washing up.