Just thought I'd pass along some knowledge that I gained a few years back. Until I knew...I never knew!
Most of us have dry chemical fire extinguishers. They work & work well, but, I never knew they had to be maintained. They can not be tested. Once used, even a tiny bit, they must be refilled or replaced. The powder gets under the valve & then the pressure leaks out. There's two things that need to be done every 6 months minimum. In a commercial circumstance it's required every 30 days. One: Look at the pressure gauge. It must be in the green. Two (this is what I didn't know): They must be shaken. The powder settles inside and after about a year it makes a cake & will not come out. Take them out of the hanger, turn them upside down. It's subtle, but you can feel the powder drop. If it does not, go from right side up to upside down several times, gently shaking while upside down until you feel the powder move. Once it moves, do it a few more times to fluff it up. If you can not get the powder to move, shake, thump, rattle until you do...or replace it.
How to use one: First, keep it where the fire won't be! Don't keep it next to the stove, keep it by the front door, next to the 'fridge, or someplace easy to see, easy to remember. Teach others where it is. If you need to deploy one, dial 911 or have someone do it, then, or while, remove from rack, remove the safety clip, aim and pull the trigger. From 6 to 10 feet away aim at the base of the flame and sweep from side to side.