I'm sure it happens all the time. Happened to me doing a pre flight / turnaround check on a 737 many years ago at gatwick (LGW). Chief fire officer approached and asked if I minded if he used the A/C for an excersise, no probs with me as A/C was on a 2 hour turnaround, he promptly called in a brake fire on stand 10, in less than a minute I was surrounded by a substantial ammount of very p***ed of firemen who had been caught on a shift change. So, my point is, to see lots of blue lights and fire engines dashing around an airport does not allways constitute an emergency.