I do know that once a pin/handle is pulled, the best thing and only thing to do is to have the extinguisher serviced. I teach shop and as I tell my students, the fire extinguisher is not to put out fires but to blow a hole through the fire to allow someone to escape the flames. I realize that most people do use a Fire extinguisher to put out a fire (I would too), but the students love to play with fire extinguishers (for some unknown reason). That is why I don't let them mess with them, in case we actually need them. Our fire plan is to get out of the building and take cover in a ditch to keep shrapnel/blast wave from hitting us. We have about 5-10 cylinders of oxygen, acetylene, CO2/argon, and propane in the shop at all times. I will try to get the tanks out if possible but I will not jeopardize my students lives over them.