Actually, Houston has only three ARFF stations...54 on the north side of the field, 92 on the south, and 99 on the west side. The last time I was flying out of IAH, one of the ARFF crews from 99's was operating at a sick call on the concourse with their Rosenbauer crash rig parked right outside.
Station 63 is at the airport entrance at Will Clayton Parkway and Lee Road with the engine, brush rig, and medic. Station 64 is on Greens Road-technically off the airport with the engine, tower, chief, and medic. They are right across the road from the ends of Runway 15R and 15L- probably 90% of the departures use these ,so it's always noisy. Years ago, a 747 used every inch of 15L leaving town and blew down a bunch of ceiling tiles over the apparatus. As far as I know, both 63 and 64 can be dispatched by the control tower for alerts on the field.