For this type of fire, I believe that the chemical type is the best regardless of the corrosiveness. For an enclosed fire like in an engine compartment with the lid closed, Halon once was the selection of choice that did the least damage. However, it is being phased out due to ozone depletion issues. Halon worked by reducing the oxygen needed to sustain a fire. This meant if used in an enclosed area like a control room, all personnel had to be out even though I've seen advertisements to the contrary.
http://palimpsest.stanford.edu/waac/wn/wn15/wn15-2/wn15-208.html
http://www.reliablefire.com/halon/halon.html
We are now specifying FM-200 for enclosed areas. Instead of depleting the oxygen, it instead changes the ignition temperature needed to sustain a fire. The attached link shows personnel in an area when FM200 releases.
http://www.e1.greatlakes.com/fm200/jsp/index.jsp