Having had to go and clean up one recently...yeah. they're not fun. For anyone else that needs the information, look up the active ingredient on the extinguisher if you need to discharge one. Mine was an "Monoammonium phosphate" type, so I had to make a baking soda mixture and get it everywhere possible, scrub, rinse, etc. I'm still apprehensive that i got everything but it is what it is. For this reason I've got a couple element's on the wall, one in each car. I've also got a "backup" traditional dry-agent extinguisher that sits next to the element sticks on the wall in the garage in the event something happens that isn't being contained by the element.
Additionally, remember that there are a few non-corrosive agents out there as well. The industry word for these are "clean agent" extinguishers and they're typically used in aircraft, server rooms, and other locations that are high-consequence for corrosive chemicals.
- As Z mentioned, CO2 is an option
- "HalGuard" produced by H3r - available in smaller handhelds
- "Novec1230" produced by 3M - LifeLine makes a portable, otherwise this is typically in plumbed systems
- "CleanGuard" produced by Ansul - available in handhelds
- "FE-36" produced by Dupont - typically in plumbed systems
I think there's another 1-2 out there as well but these are the common ones. Keep in mind they're going to be significantly more expensive than the "traditional dry chemical" extinguisher but they're an option. Typically a 2.5# for each of these is going to be around $180-$300. That was the reason i went with the element + dry chem in the garage. I've heard lots of good things about element and motorsports folks seem to use them regularly-ish with success so long as the combustible load (what's burning) isn't something you'd need a 5-10# extinguisher for anyway.
If someone's got specific questions, let me know. I work for a company that has a large traditional fire protection division and their job is extinguishers, suppression systems, detection systems, fire modeling, etc. so I can forward on any questions. That's how I found out a bunch of this anyway after my recent...experiment.