Hazardous Decomposition
When heated to decomposition, potassium hydroxide emits toxic fumes of potassium oxide. Will absorb moisture and carbon
dioxide from the air to form hazardous potassium carbonate.
http://en.wikipedia.org/wiki/Potassium_carbonate
could this vapour them attack other parts of a board in theory that is not in direct contact with the battery?
YES!
Vapour is nothing more than 'seperated liquid' just like steam is nothing more than 'seperated water' (becoming fine droplets).
The light weight of the vapour droplets mixed with warm thermal air currents from the pinball machine is more than enough to spread corrosive vapour all over your headbox boards.
MM.
