Actually Rescue 6 can be activated as a reserve rescue, the last time this happened was during the blizzard of 2005 when three firemen were killed in two separate incidents, one in the Bronx and the other in Brooklyn. 4 out of the 5 Rescue Companies responded for the firefighters trapped in the Bronx (3,1,4,and finally 5) leaving only Rescue 2 to cover the city. I believe the citywide tour commander requested Rescue 6 to be activated to cover part of the city.