I work in environmental, health, and safety, and industrial hygiene, so workplace safety is my jam. You are correct that the regs are shit. Unless you live in one of five states with heat related regulations, you’re really only covered by OSHA’s general duty clause, which can be summed up as “employers have to at least make a good faith effort to do the bare minimum to not hurt their employees”. It sucks.

For workplace temperature, what you’ll want to look at is wet-bulb temperature, not the dry-bulb reading provided by a thermostat. You can find online calculators that’ll calculate it by temperature and relative humidity. Wet bulb is the measurement accounting for evaporative cooling, so a better approximation of what temperature a human body experiences. Theoretically, a wet-bulb temperature of 35°C (95°F) or more isn’t sustainable and will always lead to heat illness with sustained exposure. Around 30°C (about 85°F) is where we start seeing issues if people don’t consider any steps to avoid heat illness.

It gets tricky from there as there are a ton of variables to determining a safe temperature, e.g., hydration, environmental radiant heat, cardiovascular health, level of acclimation, nature of the work, body mass, break frequency, access to air conditioned spaces, etc.

For example, at 94°F, a healthy adult performing moderate physical activity out of the sun (or away from any other heat source) should be fine up to about 75% humidity (so a wet bulb of 85°F), assuming they are dressed appropriately, acclimated to the temperature, remain hydrated, take periodic rest breaks in an air conditioned space (I’d advise 10 minutes on the hour, maybe more). I also recommend a monitoring/emergency response program

Let me know if I can help at all. I love heat, but working in it is just miserable.