Mick!
TreeHouser
95 degrees here tomorrow, unpleasant.
not much you can do for them except lean on the horn if you see them first.
Now, having 3 vests, its possibly for a two man crew to have continuous cooling, or a 3 man for most of the day. I usually use them mid-morning to mid-afternoon, not all day. Ifs its going to be that hot, then usually start as early as possible, do the most physical work earliest, like chipping, and knock off early, after wearing the vests for the duration.
If you have no AC, its a godsend for the drive home on hot asphalt, in rush hour/ slow traffic.
Compared to saw protection (chaps start at $60, chainsaw protective pants $120) which you hope to wear, but never use, Coolvests are money well spent. $.02