This conversation has prompted me to re-label all of ours.  They came labeled "panic button," which seems like a ridiculous label for a red button in a hallway.   For a time, we were told they actually turned off the fume hoods, which was simply false, but the rationale was that would be a good thing to do in a case of a fume hood fire and were labeled as such.

Having verified that they do in fact crank up the fume hoods (which are for the most part of a two-stage VAV design), they now bear the following legend:
"PURGE BUTTON:  In case of chemical spill or release, press to maximize laboratory exhaust ventilation."   No guarantee that pressing it will solve your particular problem, but at least it's truth in labeling.

                  Don