Heat stress prevention for high-risk crews

What is heat stress for a working crew?

Heat stress is the load heat puts on the body. NIOSH defines it as the mix of metabolic heat, environmental heat, and clothing and protective equipment, which adds up to more heat stored in the body. Your crew makes heat by working. The sun, humidity and gear add more.

The heat stress load can end in heat illness. NIOSH lists heat stroke, heat exhaustion, rhabdomyolysis, heat cramps and heat rash. It also lists plain injuries, such as slips on sweaty hands, fogged safety glasses and burns from hot equipment.

NIOSH names these risk factors:

• High temperature and humidity
• Direct sun and indoor radiant heat
• Limited air movement
• Lack of acclimatization
• Dehydration, which means not drinking enough fluids
• Hard physical work
• Protective equipment and clothing
• Health problems, some medications, age and a past heat illness

Most of these are things a supervisor can change. That is why prevention works as a plan, not a reaction.

Who is most exposed to heat on the job?

Outdoor trades carry the most exposure, but indoor crews get hurt too. BLS reports that 33.0 percent of workers had regular outdoor exposure in 2023. At least 99.5 percent of firefighters, landscaping and groundskeeping workers, and construction laborers worked outdoors on the job.

Indoor work counts as well. In 2021 and 2022, BLS counted injuries that cost at least one day away from work because of heat. The numbers below show that heat is not only a construction problem.

Source: Bureau of Labor Statistics, The Economics Daily, June 20, 2024. Warehouses sit inside trade and transportation. Plants sit inside manufacturing. Both are industry pages JMAR serves, along with construction, first responders and government crews.

How do water, rest and shade fit with hydration?

Water, rest and shade come first. OSHA encourages water, rest, and shade as prevention and as treatment for heat-related illness. Electrolytes add to that base. They never replace it.

Here is what each part means on a jobsite.

1. Water. NIOSH says water should be portable, cool (under 59°F) and near the work area. Give each worker a cup. Name who checks the supply.
2. Rest. Let workers stop when they feel heat discomfort. Shorten work periods and lengthen rests as heat, humidity and sun rise, when the air is still, when gear adds heat and for heavy work.
3. Shade. Give outdoor crews shade or a cool spot to recover. Our post on a cool-down area shows how to set one up.

How much should a worker drink?

NIOSH says to drink 1 cup (8 oz) of water every 15 to 20 minutes for moderate work in the heat that lasts less than 2 hours. It also says fluid intake should generally not exceed 6 cups per hour. More is not better. That cap is why hyponatremia matters on long shifts. Our jobsite hydration plan and the hyponatremia guide go deeper.

Where do electrolytes fit?

Sweat carries out water and salts. Electrolytes such as sodium and potassium are the salts your body needs to hold and use fluid. NIOSH says that if sweating lasts several hours, workers should drink sports drinks with balanced electrolytes. It also says to avoid salt tablets for cramps.

JMAR’s Rapid Restoration Drops are a dietary supplement. They replace electrolytes lost in sweat and support hydration. They are not medicine and not a substitute for medical care. See the liquid electrolyte drops pillar for the label facts and the format comparison for how drops stack up against other options.

How do heat index, WBGT and work/rest schedules help?

They turn the weather into a number you can act on. The heat index tells you how hot it feels from air temperature and humidity. The WBGT adds wind and solar radiation, so it suits outdoor work better. A work/rest schedule then sets how long a crew works before a break.

The National Weather Service gives a plain example. At 96°F air temperature and 65% relative humidity, the heat index is 121°F. Full sun can add up to 15°F more. OSHA says it uses WBGT to decide whether a heat hazard was present.

Read more in our guides on the heat index work/rest chart and WBGT vs heat index. For Houston-style humidity, see why 96°F can feel like 121°F.

How do you acclimatize new and returning workers?

Build heat exposure up over 7 to 14 days. Acclimatization is the set of changes the body makes after gradual heat exposure, such as sweating more efficiently. NIOSH says employers should ensure workers are acclimatized before they work in a hot environment.

NIOSH sets this schedule:

NIOSH also says to supervise new employees closely for the first 14 days or until they are fully acclimatized. The National Weather Service lists the same step: acclimatize workers on the first day in heat and after any long absence. Read the full acclimatization schedule and our post on Texas summer starts.

What training and toolbox talks does a crew need?

Train workers before hot work starts, and tailor it to your site. NIOSH says every worker and supervisor should learn the signs of heat illness, first aid, the causes and how to reduce risk, how gear adds heat, why acclimatization matters, and how to report symptoms and reach emergency services.

Supervisors need more. NIOSH adds acclimatization, emergency procedures, weather monitoring, hot weather advisories and fluid and rest checks.

A short toolbox talk keeps it fresh. Five minutes at the start of a shift is enough to cover one topic. Use our heat toolbox talk kit. Teach the buddy system too. NIOSH recommends that workers watch each other for signs of illness.

How do you build a written heat program?

Write down who does what, then train people on it. A heat illness prevention plan does not need to be long. It needs to be specific and in every supervisor’s hands.

1. Name an owner for the plan and a backup.
2. Set the water plan: where it is, how much, who checks it.
3. Set rest and shade rules by heat index or WBGT.
4. Write the acclimatization schedule for new and returning workers.
5. Add a heat alert step for days the weather service forecasts a heat wave.
6. List signs of illness and the first aid steps.
7. Write the emergency step: for heat stroke, call 911.
8. Train workers and supervisors, then review the plan each season.

Our heat stress program for employers turns this list into a checklist. For the rule side, see OSHA heat rules. OSHA’s free and confidential On-Site Consultation Program can help small and medium businesses build a heat approach.

This page is not legal advice.

How do heat-illness signs and emergencies fit in?

Supervisors must know the difference between heat exhaustion and heat stroke. Heat exhaustion is the body’s response to losing too much water and salt through sweat. Heat stroke is the most serious heat illness. NIOSH says body temperature can reach 106°F or higher within 10 to 15 minutes.

Heat stroke is an emergency. Call 911 and stay with the worker. Move the worker to shade and cool them fast while you wait. Our heat illness pillar and heat exhaustion vs heat stroke guide cover recognition, and JMAR’s emergency protocol is a printable reference.

What should a supervisor check every morning?

Check the weather, the water, the crew and the plan before work starts. NIOSH says supervisors should be trained to monitor weather reports and respond to hot weather advisories. It also tells employers to use a heat alert program whenever the weather service forecasts a heat wave.

A five-minute morning check keeps the plan alive:

1. Weather. Look at the heat index or WBGT forecast and the weather service alerts. Note the hottest hours.
2. Water. Is there cool, potable water near the work area? Does each worker have a cup or bottle? Who refills it?
3. People. Who is new, returning from time off, or working a heavy task? They need the acclimatization schedule and lighter work with longer, more frequent rests.
4. Gear. Protective clothing and equipment add heat load. Shorten work periods and add rest when gear adds heat.
5. Shade. Is there a shaded or cool spot within a short walk?
6. Emergency. Does everyone know who calls 911, and where the crew is on the site map or address?

Write the answers on the daily sheet. If a check fails, fix it before work starts, not after the first complaint.

What mistakes do crews make with heat plans?

Most plans fail in the small things. A plan that lives in a binder does not protect anyone. These are the gaps NIOSH’s guidance points at:

Each fix costs little. Most need only a decision and a talk at the start of the shift.

How do you know your program works?

Track what you can count, and review it each season. Count heat-related incidents, near misses, first aid events, missed work days and training sessions. Compare this summer to last summer with the same definitions, so the numbers mean something.

Do not rely on one number. A quiet summer can be a mild summer. Pair counts with the daily check sheet, a short crew survey and a walk of the site.

JMAR has its own calculator for estimating the cost and return of a hydration program. It is JMAR’s tool on a separate site: jmarsolutions.app. Treat its output as an estimate built on your own inputs.

Where do JMAR hydration programs fit?

They add to your plan. JMAR’s Hydration Game Plan has three steps: create the plan with your safety managers, educate crews with onsite toolbox talks, and achieve results with ongoing hydration and wellness coaching.

JMAR also supplies Rapid Restoration Drops in a 4 oz bottle and in single-serve packets, for crews that sweat through long shifts. See the hydration programs, the implementation steps and the drops product page. Health and wellness coaching is not intended to diagnose, treat, prevent or cure any disease or condition.

Next step

Book a free 15-minute demo with JMAR at calendly.com/jen-jmarsolutions/15-min-meeting. You can also ask for a free sample or request bulk and government pricing.