Heat safety for outdoor work in a Phoenix summer

Heat advice for Phoenix is usually written for people who have the option of going inside. For the roofer, the landscaper, the utility crew and the delivery driver, that option does not exist, and a list of things not to do is not a plan. What the climate actually gives a person working outdoors in Phoenix is a set of hours, and the first job is finding out honestly how few of them there are.

Everything below is a climate normal: the average of the thirty years from 1991 to 2020, recorded at Phoenix Sky Harbor International Airport, station USW00023183. It describes a typical July, not next Tuesday. The distinction matters most in this article, because a schedule built on a normal is a schedule built on the middle of a distribution, and the days that hurt are at the edge of it.

The shape of the problem

Read the July line and the scale of the thing is plain. It does not dip into the eighties at night, it dips into the middle eighties, and it does so for about three hours. The normal July hour is at or above 90 °F for eighteen hours of the twenty-four, and at or above 100 °F for nine of them: noon to 8 p.m.

That is a monthly mean, which means something a person should be clear about: it is the average of a whole month, so the actual afternoons run either side of it. The number to hold on to is not 105 °F. It is that the coolest normal hour in July is 86 °F, and it arrives at five in the morning.

The table is the argument for treating this as a five-month problem for outdoor work rather than a two-month one. September has no normal hour at 100 °F and still has eleven hours at or above 90 °F; May has seven hours at or above 90 °F before the working year has even warmed up. Both are months when a crew from a cooler climate will underestimate the day.

Step one: find the hours the schedule actually has

The workable window is a subtraction, and it is worth doing it out loud rather than assuming it.

In July the normal hour is above 95 °F from 11 a.m. to 9 p.m., and the only hours below 90 °F are the small hours. There is no useful window. What there is instead is a decision about which part of the day the heaviest work sits in, and a recognition that “we start early” means four in the morning rather than seven.

June and September are where an actual shift can be built. Both have a normal hour of 79 °F, and both hold below 90 °F until mid-morning. In September the normal hour is still 99 °F at four in the afternoon, so an early start buys something real. In June the same is true of the first half of the month, before the ramp takes it.

The Heat-Safe Hours Planner is built for exactly this question: an hour-by-hour read of a typical day in a given month, scored against what the activity can take. It is a better tool than a rule of thumb here, because the ceiling for lifting roofing material and the ceiling for driving a route are not the same number.

Step two: treat the first two weeks as the dangerous ones

The single most useful idea in the occupational guidance is acclimatisation, and it is not a comfort measure.

A body that has been in a cooler climate does not sweat or regulate as effectively as one that has spent a fortnight in Phoenix, and the people most at risk are the newest ones. OSHA’s heat campaign frames this as the reason a gradual build-up belongs inside the schedule rather than outside it: the new starter and the worker back from two weeks away are both in the same position, and neither is served by starting on a full load on day one.

How that is done is a supervision judgement, and this page does not attempt it. What the climate record says is narrower and more useful: that in July the margin for error does not exist in the middle of the day, so the fortnight to build tolerance is a fortnight to be careful about which hours the work occupies.

Step three: water on a schedule, not on thirst

OSHA’s campaign is built on three words (water, rest, shade) and the order is not a ranking. Water alone does not solve a day at 105 °F, and rest alone does not solve it either.

The reason thirst is a poor trigger is that it arrives after the deficit rather than before it, which is why the official guidance is to drink on a schedule through the shift rather than in response to feeling dry. How much depends on the person, the work rate, the clothing and the day, and it is not a figure this page can set.

Maricopa County’s own heat guidance, and the CDC’s, both treat water as one input among several rather than as the answer. The heat-illness triage guide on this site is the place to look when the question changes from prevention to recognition.

Step four: shade, and the surface underfoot

Shade is the third of OSHA’s three words and the one most often treated as a luxury. On a July afternoon with a normal hour at 104 °F, shade and direct sun are not the same job, and the site’s Pavement & Paw Check exists because the surface is a separate problem again: an asphalt lot in full sun runs far above the air temperature, and the person kneeling on it is in contact with the hottest thing on the site.

The practical form of this is scheduling the shaded work for the middle of the day and the exposed work for the edges of it. It is a smaller intervention than it sounds, and it is one of the few that costs nothing but planning.

Step five: know the two signs that stop the job

The difference between a bad afternoon and an emergency is recognition, and both NWS Phoenix and the CDC publish the symptom lists this site quotes.

Heat exhaustion is the one that stops a person working. The CDC’s list is heavy sweating, weakness or fatigue, dizziness, headache, nausea, muscle cramps and skin that is clammy and moist. The first aid in the same guidance is to get the person out of the heat, cool them down and give them cool water to drink, and the guidance is also where the details belong rather than here.

Heat stroke is the emergency. The signs the CDC names are a body temperature of 103 °F or higher, hot skin that may be dry or may be sweating heavily, confusion, slurred speech and loss of consciousness. The instruction that goes with it is unambiguous: call 911 first, and cool the person while waiting. The triage guide on this site exists to get somebody to that conclusion quickly.

Rhabdomyolysis is the third condition on the CDC’s list and the one least known outside occupational settings: it shows up as muscle pain, weakness and dark urine after heavy exertion in heat, and the CDC’s own warning is that the symptoms alone cannot tell you whether you have it. That is a reason to treat it as a medical question rather than a hydration one.

What this page does not do

This is a page about a climate, not a page about a person. It does not diagnose, it does not set a water or salt figure for anyone, and it does not tell a supervisor how to run a crew. The symptom lists above are the agencies’ own wording, repeated so a worker can recognise them, and the response is theirs, not this site’s.

What it can say with confidence is what the thermometer does, hour by hour, in a normal Phoenix July. That is the constraint the rest of the guidance is written around, and it is the reason the answer to “when should this work happen” is usually “before five in the morning, or not at all”.

The Heat-Safe Hours Planner will give you the hours; the triage guide is for the moment the schedule has stopped mattering. If you are reading this because someone is unwell in the heat now, go to the triage page and call 911 for confusion, fainting or hot dry skin.