system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 - How does a fire extinguisher go bad if it has never been used and the gauge shows it to be charges & ready to go?
gpt
Fire Extinguishers expire for three main reasons - 

1) they are not perfect containers and small gas leaks overtime will empty them. 

2) the chemical agents inside the container can degrade/decompose/solidify over time meaning they're function as intended in an emergency. 

3) the gauge is a point of failure, the dial can break/get stuck and you might not know it's 'gone bad' until you really need to use it. 

You don't want to make assumptions or "take a risk" if you need to put our a fire at that very moment, so we have policies and expiration dates that take the above into account and simply say, even if you *think* the extinguisher is still good, it's reached it's end of life and should be replaced.