The dry chem powder can irritate your lungs, eyes, skin, etc. but that's pretty much it. If you're asthmatic, I suppose it could trigger an attack.
To clean up, I believe it is generally recommended that you sweep or vacuum the powder up. Don't use water. You're right, it's corrosive. I would kiss the electronics in my TV or computer good-bye, probably, if I ever had to blast it with dry chem powder.
I'm taking an 8-week emergency preparedness course now and we did the fire extinguisher training a couple weeks ago. They have this bucket of water hooked up to a BBQ propane tank that bubbles up the propane from the bottom of the bucket. Since propane is heavier than air, it just forms a layer in the bottom of the bucket, floating above the water. Everyone in the class took turns practicing PASS. A fire fighter just used a road flare attached to a pole to relight the flame between students. We did kick up quite a bit of dry chem powder.