With the Helite (like Bill wears) you just change the CO2 cartridge. They run around 50 bucks IIRC. They are 100CC or so-much larger than a standard.
Assuming one hasn't punctured the vest, swap out spent for new and on your way. About 10 min.
Almost impossible to activate it by forgetting to unclip. It takes quite a pull to activate. When we had demos at our riding club I really had to use some body english and a very hard tug to get the vest to go off.