There is no guarantee OC is going to prevent an attack. I've had people literally wipe it from their eyes and keep coming. The same thing can be said for tasers, you can't be 100% certain either is going to stop someone.
I personally watched someone pull taser probes from his chest and get very violent. It took 6 of us in the jail to subdue him . True story that guy was a beast and yes he was on drugs