Working Outdoors Through a Phoenix Summer

If somebody working in the heat becomes confused, stops making sense, collapses, or stops sweating, call 911. That is not exhaustion. Cool them and call.

Heat tolerance is something your body builds, and it is something your body loses. It is not toughness, it is not experience, and it is not a personality trait. It is a physiological adaptation with a build time measured in days and a decay time measured in about a week.

Which produces the single most useful and least known fact on this page: the most dangerous shift of the summer is often the first one back.

What acclimatisation actually is

The National Institute for Occupational Safety and Health defines it plainly: acclimatisation is “the beneficial physiological adaptations that occur during repeated exposure to a hot environment.”

So it is real, it is measurable, and it is the reason two people doing identical work in identical heat are not at identical risk. The one who has been out there for three weeks is not braver. Their body has changed.

The schedule NIOSH recommends, quoted exactly

This is written for employers, and it is worth knowing as a worker, because it gives you a standard to measure against.

For a new worker: “the schedule should be no more than a 20% exposure on day 1 and an increase of no more than 20% on each additional day.”

For a worker who has done the job before: “no more than a 50% exposure on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.”

And the reason the two differ, in NIOSH’s words: “New workers will need more time to acclimatize than workers who have already had some exposure.”

Nobody’s first day should be a full day. If you are new and you are being put straight onto a full shift in July, the recommendation you are working outside of is a federal one, and it exists because this is the population heat kills.

The part almost nobody knows: a week away undoes it

NIOSH again, and read this one twice: “If they are absent for a week or more then there may be a significant loss in the beneficial adaptations leading to an increased likelihood of heat-related illness and a need to gradually reacclimate to the hot environment.”

A week of vacation. A week off sick. A week of rain, or indoor work, or a project that moved inside. Then back onto the same job, in the same heat, with the same confidence — and measurably less protection than when you left.

The good news is that it comes back fast. NIOSH: “It can often be regained in 2 to 3 days upon returning to a hot job.” So the fix is not dramatic. It is two or three deliberately easier days, and it is the cheapest injury prevention available to anybody.

What the CDC says to do on an ordinary day

From the CDC’s guidance for people who work outdoors:

Drink water before you are thirsty. Their wording is “Drink plenty of water, and don’t wait until you are thirsty to drink.” Thirst is a lagging indicator, and in this climate it lags by too much.

Skip alcohol and sugary drinks — CDC says “Avoid alcohol or liquids containing large amounts of sugar.”

Wear “a brimmed hat and loose, lightweight, light-colored clothing,” and use sunscreen as the package directs.

Move the work, not just the worker. CDC’s own suggestion is to “Ask if tasks can be scheduled for earlier or later in the day to avoid midday heat.” That is a question an employer can answer yes to more often than people ask it.

And get properly cool, not just out of the sun — “Spend time in air-conditioned buildings during breaks and after work.” Shade is relief. Air conditioning is recovery.

The stop rule

CDC gives one instruction in capital letters, and it is the one to memorise:

If you feel faint or weak, “STOP all activity and get to a cool place.”

Not finish the row. Not finish the roof. Not wait for the break. The reason it is written that way is that the judgement you would use to decide whether to push on is made by the organ heat affects first.

Tell somebody. A person cooling off alone in a truck is a person nobody is watching.

When it stops being a heat problem and becomes an emergency

Confusion, slurred or strange behaviour, collapse, seizure, or skin that has gone hot and dry after heavy sweating — call 911. Those are not signs of somebody who needs a break. The dividing line between the two conditions, and what to do in the minutes before help arrives, is covered properly in heat exhaustion or heat stroke.

Our emergency rooms are open every hour of every day and are walk-in, with CT, X-ray and a full laboratory in the building. Go to the nearest one — and if another emergency department is closer to where you are working, that one is the right answer.

If you are unsure, come in — this list is not exhaustive and you are not expected to assess yourself in the heat that is affecting your judgement.

Questions people actually ask

I have worked outside here for fifteen years. Does any of this apply to me? The daily habits, yes. And the week-away rule applies to you exactly as much as to a new hire — NIOSH does not carve out an exception for experience, because the adaptation decays regardless of how long you took to build it.

My employer will not reschedule anything. The recommendations above are the federal occupational-health ones, and they are public and citable. What you can control alone is water before thirst, real cooling on breaks, and the stop rule.

Is drinking a lot of water enough on its own? No. Water is necessary and it is not sufficient — acclimatisation, cooling and timing all do work that water cannot do.

What if I am on medication? Some common medicines change how the body handles heat, and this page is not the place to work that out. Ask your prescriber or a pharmacist — and do not stop or change a medicine because of something you read on a website.

I felt dizzy yesterday and I was fine after sitting down. Do I need to do anything? Treat it as information rather than as a scare. It happened for a reason, and the reasons are on this page. If it happens again, or if it comes with confusion or vomiting, stop and get seen.

---

If somebody is confused, collapsed, or has stopped sweating, call 911. For heat illness that needs more than a break, both of our emergency rooms are open 24 hours a day, every day of the year — walk in, no appointment and no referral. Find your nearest emergency room →

Related reading: heat exhaustion or heat stroke · which door do you need

Sources

22. Heat and Outdoor Workers — Centers for Disease Control and Prevention. https://www.cdc.gov/heat-health/risk-factors/heat-and-outdoor-workers.html
23. Heat Stress — Acclimatization — National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention. https://www.cdc.gov/niosh/heat-stress/recommendations/acclimatization.html

This article is general information, not a diagnosis, and it cannot account for your health or your medications. If you are unsure, come in — this list is not exhaustive and you are not expected to assess yourself. If it might be an emergency, treat it as one and call 911.