Practically speaking, how do inspection services or fire departments do this for a school, office, or apartment building that has multiple extinguishers scattered about in halls, stairwells, and other random rooms? Other than the annual “rag and tag” inspection it seems too involved to to do on-site. I can’t imagine wheeling around a cart around is very cost-effective if it’s even possible to fit all the equipment on one. Do they have a special truck with testing equipment? Do they just swap them out for ones that were already refurbished at a central facility?
My business has 4 fire extinguishers.
For the annual inspection, there isn’t much to do. They just check them and go.
For the more in depth service, they just swap them out.
A lot of places will come to your location to do the annual rag and tag. Some places have the ability to do the annual inspection on the road, so they can come out to your location and do it. Or, at the very least, they’ll take yours out, drop in some temporary ones, and bring yours back when they’re done with whatever they need to do.
My place has 3. Once a year I bring them to the inspection place and then bring them back. Yes, it means my building is without any extinguishers, but it’s only for an hour or two.
What would be nice, now that I’m thinking about it, is if they could make a small change, from annual inspections to every other year. That would give us, and more importantly, bigger places, the ability to bring in half our extinguishers this year and half next year so the building isn’t lacking protection while they’re out.
And, yes, I could just bring in half of them one day and half another day, but if I can avoid making 4 trips out there, I’d prefer it.
That was my thinking. I have a large concrete patio that would be a safe place to start a fire, but if I used the old extinguisher on it how would I clean up all the dry chemical powder?
That’s what an Arby’s is for. It’s not like there’s anyone there anyway.
Leaf blower into the neighbors yard? 
I’ve heard that some of those powders turn to a clay-like substance if they get wet. I’d probably try to vacuum (with a shop vac) or sweep up as much as possible and hold off hosing it down until it’s just dust. Some quick googling mentions using rubbing alcohol, but I suspect that’s for places like a kitchen where you don’t want to take a pressure washer to it.
I did have some friends once blow one off in a dorm room. I never did follow up how they cleaned it, but they said it was everywhere.
The company that I worked for has vans that are set up to do any inspection, service or repair short of the Hydro Static testing which needs to be done at a DOT licensed station.
You also check the bottom to be sure there’s no rust and check the rubber hose to be sure no cracks are developing. And you sign/date the tag. Without an up to date tag, OSHA can fine you.