Even in Montana there are times during the growing season when the temperature stays above 90o F. High air temperatures coupled with low humidity put agricultural workers at special risk of heat illness. Worker Compensation claims for heat illness among agricultural workers are among the highest of any occupation.

Pesticide handlers and early entry workers are at even greater risk. The special clothing and equipment they wear for protection from exposure to pesticides can restrict the evaporation of sweat, blocking the body's natural way of cooling itself, which results in a buildup of body temperature. Exposure to certain pesticides can also produce sweating and there can be combined effects with exposure to heat. In addition, pesticides are absorbed through hot, sweaty skin more quickly than through cool skin. 

What is heat stress?

Heat stress occurs when the body builds up more heat than it can cope with. Heat stress is not caused by exposure to pesticides, but may affect pesticide handlers working in hot conditions. Wearing personal protective equipment (PPE) which protect the body from contact with pesticides can increase the risk of heat stress by interfering with the body's natural ability to cool down.

When the body becomes overheated, less blood goes to the active muscles, the brain, and other internal organs. Workers get weaker, become tired sooner, and may be less alert, less able to use good judgment, and less able to do their jobs well.

During hot weather, heat illness may be an underlying cause of other types of injuries, such as heart attacks on the job, falls, and equipment accidents arising from poor judgment.

Avoid Heat Stress

Several factors work together to cause heat stress. Before beginning a pesticide-handling task, think about whether any of these factors are likely to be a problem. Consider making adjustments in the task itself or in the workplace conditions, including:

  • Heat factors - temperature, humidity, air movement, and sunlight;
  • workload - the amount of effort a task takes;
  • personal protective equipment (PPE);
  • drinking water intake; and
  • Scheduling.

Heat and Workload

High temperatures, both low and high humidity, and sunlight increase the likelihood of heat stress. Air movement, from wind or from fans, may provide cooling. Because hard work causes the body to produce heat, a person is more likely to develop heat stress when working on foot than when driving a vehicle or flying an aircraft. Lifting or carrying heavy containers or equipment also increases the likelihood of overheating.

Cooling Systems and shade

Use fans, ventilation systems (indoors), and shade whenever possible. A work area or vehicle sometime can be shaded by a tarp or canopy or provided with fans, awnings or air conditioners. Consider wearing cooling vests-garments with ice or frozen-gel inserts that help keep the body cool.

Allow time to adjust

People who have become used to working in the heat are less likely to be affected by heat stress. To become adjusted to hot work environments, do about two hours of light work per day in the heat for several days in a row; then gradually increase the work period and the workload for the next several days. An adjustment period of at least seven days is recommended. If the warm weather occurs gradually, handlers may adjust naturally to working in hot conditions.

Personal Protective Equipment (PPE)

Pesticide handling tasks often require the use of extra clothing layers and other PPE. These items keep pesticides from getting on the skin, but they also interfere with natural body cooling that happens when sweat evaporates. A person can get overheated quickly when wearing PPE.  Select a level of PPE appropriate for the pesticide being used with the pesticide label itself as a guide to the minimum PPE. Use personal experience and PPE selection guides to help decide whether more protection is needed. Do not over-protect if heat stress is a concern, but wear whatever is necessary. In general, the more protective the PPE is, the more it adds to the heat load.  PPE that is designed to be as cool as possible or that provides a cooling effect, such as a powered air-purifying respirator or, when appropriate, back-vented coveralls.  Whenever it is practical, choose coveralls that allow air to pass through. Woven fabrics (cotton, or cotton-polyester blends) allow air to pass through fairly easily. Rubberized or plastic fabrics and fabrics coated with chemical-resistant barrier layers allow almost no air to pass through. Non-woven polyolefin (Tyvek®) fabrics allow little air passage. Non-woven polypropylene and polyester/wood pulp fabrics vary in their resistance to air flow, depending on how they are constructed.

Drinking Water Intake

Evaporation of sweat cools the body. Under the conditions that lead to heat stress, the body produces a large amount of sweat. Unless the water lost in sweat is replaced, body temperature will rise.  Drink plenty of water before, during, and after work during heat stress conditions. Do not rely on thirst alone to guide you. A person can lose a dangerous amount of water before feeling thirsty, and the feeling of thirst may stop long before fluids are replaced. Also, just because you don't seem to be sweating, don't be fooled that you are not losing water. When the humidity is low, sweat may be evaporating from your skin.  You may not feel the need to drink water if you think that you are not sweating.  As a minimum, you need to drink 1 to 2 quarts of water per hour.  Drink more water if you are working hard or are wearing additional PPE.


When the combination of temperature, sunlight, humidity, workload, and PPE is likely to lead to overheating, use scheduling to avoid heat stress.  Schedule tasks requiring the heaviest workload or the most PPE during the coolest part of the day.  When heat stress risk is high, schedule frequent breaks to allow the body to cool. Consider using a work/rest cycle guide to decide how long to work before taking a break.

Remember that people differ in their ability to work in hot conditions. Most work/ rest cycle guides are based on an average of many people who are adjusted to the heat and the workload. Workers who have not had time to adjust should work less time than the guide indicates.

When using recommended work/rest cycles, continue to be alert for possible heat-stress problems. Anyone who gets dangerously hot should stop work immediately and cool down. If necessary, shorten the time between breaks.

Stop work

The above steps will prevent most heat stress problems. But under extremely hot conditions when cooling devices cannot be used, it may be necessary to stop work until conditions improve.

This publication was adapted from "Avoiding Heat Stress" which was produced through the cooperative efforts of the U.S. Environmental Protection Agency and the Extension Service, U.S. Department of Agriculture (USDA)

Symptons: Heat vs. Pesticides

It is important to note the differences between the three heat-related illnesses and illness brought on by the use (or misuse) of pesticides. Heat-related injuries are largely brought on by heat and dehydration -- and with proper care it is possible to prevent them.

Review the following symptoms and note the differences between heat exhaustion (one type of heat injury) and those symptoms that occur with certain types of insecticides.

Heat Exhaustion Symtoms

  • Sweating
  • Headache
  • Fatigue
  • Nausea
  • Dry membranes
    • Dry mouth
    • No spit present
    • No tears
  • Fast pulse
  • Dilaterd pupils
  • Central Nervous System (CNS) depression
    • Loss of coordination
    • Confusion
    • Fainting

OP/Carbamate Insecticide Poisoning Symptoms

  • Sweating
  • Headache
  • Fatigues
  • Nausea and diarrhea
  • Moist membranes
    • Salivation
    • Spit present
    • Tears
  • Slow pulse
  • Small or pinpoint pupils
  • Central Nervous System (CNS) depression
    • Loss of coordination
    • Confusion
    • Coma

Types of Heat Injuries

Heat Exhaustion

Heat exhaustion is a milder form of heat-related illness that can develop after several days of exposure to high temperatures and inadequate or unbalanced replacement of fluids. Those most prone to heat exhaustion are elderly people, people with high blood pressure, and people working or exercising in a hot environment.

Recognizing Heat Exhaustion

Warning signs of heat exhaustion include the following:

  • Heavy sweating
  • Paleness
  • Muscle cramps
  • Tiredness
  • Weakness
  • Dizziness
  • Headache
  • Nausea or vomiting
  • Fainting

The skin may be cool and moist. The victim's pulse rate will be fast and weak, and breathing will be fast and shallow. If heat exhaustion is untreated, it may progress to heat stroke. Seek medical attention immediately if any of the following occurs:

  • Symptoms are severe.
  • The victim has heart problems or high blood pressure.

Otherwise, help the victim to cool off, and seek medical attention if symptoms worsen or last longer than 1 hour.

What to Do

Cooling measures that may be effective include the following:

  • Cool, nonalcoholic beverages, as directed by your physician
  • Rest
  • Cool shower, bath, or sponge bath
  • An air-conditioned environment
  • Lightweight clothing

Heat Stroke

Heat stroke occurs when the body is unable to regulate its temperature. The body's temperature rises rapidly, the sweating mechanism fails, and the body is unable to cool down. Body temperature may rise to 106°F or higher within 10 to 15 minutes. Heat stroke can cause death or permanent disability if emergency treatment is not provided.

Recognizing Heat Stroke

Warning signs of heat stroke vary but may include the following:

  • An extremely high body temperature (above 103°F, orally)
  • Red, hot, and dry skin (no sweating)
  • Rapid, strong pulse
  • Throbbing headache
  • Dizziness
  • Nausea
  • Confusion
  • Unconsciousness

What to Do

If you see any of these signs, you may be dealing with a life-threatening emergency. Have someone call for immediate medical assistance while you begin cooling the victim.  Do the following:

  • Get the victim to a shady area.
  • Cool the victim rapidly using whatever methods you can. For example, immerse the victim in a tub of cool water; place the person in a cool shower; spray the victim with cool water from a garden hose; sponge the person with cool water; or if the humidity is low, wrap the victim in a cool, wet sheet and fan him or her vigorously.
  • Monitor body temperature, and continue cooling efforts until the body temperature drops to 101-102°F.
  • If emergency medical personnel are delayed, call the hospital emergency room for further instructions.
  • Do not give the victim alcohol to drink.
  • Get medical assistance as soon as possible.

Sometimes a victim's muscles will begin to twitch uncontrollably as a result of heat stroke. If this happens, keep the victim from injuring himself, but do not place any object in the mouth and do not give fluids. If there is vomiting, make sure the airway remains open by turning the victim on his or her side.

Heat Cramps

Heat cramps usually affect people who sweat a lot during strenuous activity. This sweating depletes the body's salt and moisture. The low salt level in the muscles causes painful cramps. Heat cramps may also be a symptom of heat exhaustion.

Recognizing Heat Cramps

Heat cramps are muscle pains or spasms -- usually in the abdomen, arms or legs – that may occur in association with strenuous activity. If you have heart problems or are on a low-sodium diet, get medical attention for heat cramps.

What to Do

If medical attention is not necessary, take these steps:

  • Stop all activity, and sit quietly in a cool place.
  • Drink clear juice or a sports beverage,
  • Do not return to strenuous activity for a few hours after the cramps subside, because further exertion may lead to heat exhaustion or heat stroke.
  • Seek medical attention for heat cramps if they do not subside in 1 hour.

Heat Rash

Heat rash is a skin irritation caused by excessive sweating during hot, humid weather. It can occur at any age but is most common in young children.

Recognizing Heat Rash

Heat rash looks like a red cluster of pimples or small blisters. It is more likely to occur on the neck and upper chest, in the groin, under the breasts, and in elbow creases.

What to Do

The best treatment for heat rash is to provide a cooler, less humid environment. Keep the affected area dry. Dusting powder may be used to increase comfort, but avoid using ointments or creams – they keep the skin warm and moist and may make the condition worse.

Treating heat rash is simple and usually does not require medical assistance. Other heat-related problems can be much more severe.


Updated on: 01/03/08