Wow, what a idea — canceling due to heat! Here in the frigid north, we mostly have to worry about canceling because of snowstorms or ice storms. Guess we all have our own extreme weather to worry about.
I'm attaching the cancelation procedure that our organizing group came up with a couple years ago. The short version is that the person responsible for opening the hall that night makes the call about weather safety by Saturday morning, with help from other committee members if needed. We've only had to implement this once, and it was a morning of many phone calls between band members, committee members, caller, etc. (some of the band members were willing to drive through the snow and ice, the caller and other band members weren't, so it was tricky), and a pretty heart-wrenching decision overall. We've maybe canceled two dances in 15 or 20 years.
For what it's worth, we set up our fans so that some of them suck air in and others blow air out, to keep the airflow moving as much as we can. (We have 3 or 4 box fans in the windows on on each side of the hall, other windows and all the doors open, overhead fan on, extra fans for the stage and band.) I would guess that we often dance in 80+ degree heat with 80% or 90% humidity in the summer. Dancers are good about drinking water, sitting outside or in the basement to cool down, or going for a dip in the local swimming hole after the dance! (I like your popsicle and ice policy, Concord...)
Good luck,
Dana
Montpelier, VT