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I have never been to Arizona. I've been in Georgia and North Carolina though for many years, where the humidity levels contribute to make even 100 F feel like it's over 110 F. But summer heat isn't the biggest heat hazard I've had to deal with personally.
The hottest I've worked in is around 140 F ambient. I've had a couple times where my boots got "squishy" and more than once where I could push my fingers into my hard hat and leave dimples. And that's as an engineer. Granted I've worked a lot around thermal processes (kilns, cupolas, furnaces) where it's not just air temperature either but thermal radiation that will get you faster than conductive heating. Standard workwear in those places starts at FR rated clothing and then increases to things like aluminized fire suits or even up to "100 cal/cm^2 suits" (it existed well before arc flash). These companies have lots of experience with those conditions.
Stuff I've tried over the years:
1. Cooling helmets/hoods either with just air or vortex coolers.
2. Cooling vests that have some kind of liquid or gel in them.
3. Cooling vests attached to an air line with either just air or vortex coolers.
In every case the result is the same. It can HELP but it adds significant weight and if there's an air line involved, you're tethered and it always gets in the way. In the end unless the task is pretty much stationary none of these are worth the money or additional work required to use them. If that's the case then it is certainly possible to perform a job over an entire shift even at up to 140 F which is the temperature that one worker is exposed to at a railroad wheel manufacturing plant last I knew when I worked for a company that made railroad wheels. Otherwise, this stuff is just cumbersome and really doesn't do a whole lot of good.
The end result is that you do a lot more preparation ahead of time because the goal is to suit up, do the job, and undress as quickly and efficiently as possible. As the temperature climbs, the danger gets worse and it is not necessarily obvious especially without experience when you are in trouble until after the fact. For the temperatures you are talking about I would limit exposure to 15-20 minutes at most and that is with people that are already acclimated to hot summer weather. Rotate with a partner if the job takes longer than tat. There is a chart with exact values floating around in some standard somewhere. Two other important considerations are diet and hydration. Feeling "thirsty" occurs well past the point of dehydration. Urine should be clear or tinged slightly yellow and is the best non-medical way to tell if hydration is sufficient. Most people can "self medicate" as far as this goes. The second problem is electrolyte loss, especially potassium. Some salt helps (Gatorade) but isn't really all that great. Better is to routinely eat a slice of cantelope or one or two bananas every day which are both rich in potassium.
Typically when the summer season hits and you got a new guy on the crew, you have to watch them very carefully. What usually happens is that you give them all this information. Then they ignore it. When they get home the first day, they are cramping up and don't feel good. They drink a cold beer or two to "cool off", and don't eat because they don't feel good. After about 2 solid days of this regimine, I've seen them turn the color of leaf green and puke their guts out. Then it takes another 3-4 days sitting at home (without pay) to recover enough to come back to work. If they are slow learners, they might repeat the exercise a couple more times before they either wash out or decide that perhaps when they get trained on dealing with high temperature work environments, they need to pay attention.
I've personally gone into heat stress, mild heat stroke, and heat exhaustion more than once and not just on the job, and some of the incidents were actually outdoors in Michigan. Heat related injuries are not just a Southern thing.
As a company, the best strategy is to do the training. Put up "urine color" signs in the bathrooms. Encourage even office employees to get out of the office at least a couple hours a day. After 7-10 days of at least 2 hours of exposure a day, personnel will be acclimated to the temperature (works hot or cold). Freely give away as many bananas as possible...they're cheap. Same with making "Squincher" (tastes a lot better) or "Gatorade" drinks. Monitor employee activities. Be very strict about how much exposure time is allowed and regular rotations. Cut back of crazy amounts of overtime too because getting a good meal and a good night's sleep is important for recovery. Now is not the time to be macho. Save that for the dark and dreary, stormy nights. The whole idea is to encourage good habits when it comes to hot weather. And if the company isn't supporting this sort of stuff and I'm supervising a crew, I won't hesitate to buy bananas for $1 or a whole case of "icee"s or splurge and buy the fancy fruit bars or something like that for a reward during summer months. It's a super cheap way to score brownie points while in reality you're just keeping them hard at work on the job instead of laying out.
This is truly an area where "your brother's keeper" applies. If you are on a crew and working under high temperature conditions you need to frequently check on each other and frequently have a quick discussion about how you look/feel with each other and whether it's time to stop. This is the time where watching the clock is a good thing, and watching out for each other is important, just as when using spotters when doing hazardous work such as fire watches, confined space watches, and ground men/energized work watches.
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