When I was fresh out of the Army and we were just starting out, I worked at a sawmill in Juliaetta, Idaho. I worked loading lumber into boxcars. We had a thermometer down under the loading docks, in the shade, and our highest reading was 112F. We had no shade. I don't know what the temp was inside a black boxcar on a 100+ day but it was damn hot. You had to be careful not to touch the car or you would get burnt. On a typical day we would load two boxcars full; roughly, 100,000 board feet. My wife would send a gallon of iced tea with me in the morning and I would have drunk that by noon. I would fill the jar with cold water for the afternoon (kept it in a pile of sawdust). I wore a headband to keep the sweat out of my eyes. When I got home from work, I would soak in a tub of cool water.
One of the partners I had was a recent transplant from Bakersfield and I don't think the guy even sweated. Little, wiry guy who seemed to thrive on the heat. Another guy, a big husky guy, about 220, lasted most of one day and had to go home. GD