Foam systems are typically used where highly flammable materials need protected... like oil refineries, alcohol facilities, or in this case, jet fuel. They are deluge systems (all heads open for total coverage upon emergency), dry systems are for cold/outdoor use (and are equipped with sealed, fusible heads and filled with air).

The foam is relatively inexpensive, but it will still likely cost them upwards of $10,000 to have their system serviced/re-filled (maintenance typically doesn't touch the sprinklers are you need special certifications/insurance to work on them). That's besides the cleanup cost. Still much cheaper than the potential loss of life and aircraft that a hangar fire could cause.

I know we would get our asses chewed out by the fire marshal for false alarms (whether or not we caused them), so I imagine there is quite a bit of shit flying around after this mishap.

Source: Former sprinkler fitter