This is going to be more of a life pro tip, but trying to reach the largest audience here.
Just had a frantic neighbour knocking at my door saying there is a fire in her oven.
I was over there in under 60 seconds with the fire extinguisher. There was a pot of oil on fire wedged between the element and the rack. No way to quickly and safely remove it, so I blasted it.
If I had tried to remove the pan, it’s likely it would have ended up spilling burning oil everywhere and making the situation much worse. Now they just have a house full of dust to clean.
Will replace our extinguisher today and am considering buying a few more to gift this Christmas.
As I pointed out in another comment, leaving them untouched and not turning them over to get the dust inside the can moving around and not stuck settled at the bottom is a real issue. To “test” them you basically ensure that the pressure is still where it needs to be and turn them over to get stuff unstuck from the bottom. That’s all I was referring to.
The fact that no one has touched them in two and a half years leads me to believe that all the dust is settled at the bottom of the extinguisher, and when an emergency arises, they won’t function properly.