Yes Tom, I know about Field Approvals and the requirements and processes they entail.
As for cleaning things up, depending on which agent was in the extinguisher, there are three different processes. All of the agents used are considered to be corrosive when left in place for any length of time. All require neutralization as part of the clean up.
One powder in use requires an isopropyl alcohol wash at a certain concentration, the second type requires an acidic wash with a certain concentration, and the third version requires a baking soda paste scrub with a soap and water wash. The longer the agent sits on something, the worse the corrosion gets.