Working in the heat and humidity is a killer (literally). When I was doing damage appraisals in the summer in Dallas and had to visit bodyshops a lot of them had signs advising folks that due to the extreme heat AND humidity vehicle delivery times may need to be extended. I would usually extend rental because I understood that working in the heat zaps your energy especially if you're welding or other activity which adds to the already hot enviorment. I could tell some of those techs where really hurting around 3 or 4 pm (hottest time of the day in DFW) and the THI was around 120. I experienced this first hand changing out the clutch on my mustang in August. No amount of fans and water helped, in fact there was a point where my wife came into the garage and told us to stop and take a break because my BIL and I where pale as ghosts. After we finished Sunday night I was completely exhausted and got leg cramps that night. I love working on cars but temperature extremes require you to take more breaks and work a little slower and remember to drink lots of water, a buddy of mine who was in Iraq advised me if you aren't peeing you need to drink more water. Remember Heat exhaustion or heat stroke is no joke, and the older we get the more susceptible we are to it, so take it easy, take lots of breaks and drink lots and lots of water (save the beer for later).