Heat & Cold Stress

Working in Extreme Temperatures

Working in extreme temperatures, hot or cold, can inundate the body’s temperature control system. When the body is unable to warm or cool itself properly, illness can result. Heat and cold stress can contribute to adverse health effects that range in severity from discomfort to death.

When to Contact EHS

EHS can conduct exposure assessments and assist departments with the development of procedures to minimize the adverse effects of heat and cold stress amongst their employees. Additionally, EHS can provide training to employees who work in these conditions.

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Shaundree Davis
Senior Program Manager

Heat Stress Facts


For many people, summertime at Princeton means warm, comfortable days, perfect for eating outside or long walks during breaks from air-conditioned offices. But for some of us, summertime means special projects working outside in the direct sunlight or renovating buildings with no cooling systems. Working in hot conditions may pose special hazards to safety and health. This document provides an overview of the variety of illnesses and injuries associated with heat stress and gives guidance on how to recognize and prevent them.

How Your Body Reacts to Hot Conditions

Four environmental factors affect the amount of stress a worker faces in a hot work area: temperature, humidity, radiant heat (such as from the sun or a furnace) and wind speed. Individuals with high blood pressure or some heart conditions and people who take diuretics (water pills) may be more sensitive to heat exposure.

The body defends itself from heat through three mechanisms: breathing, sweating, and changing the blood flow. The first reaction is to circulate blood to the skin, which increases skin temperature and allows the body to give off some heat. During heavy work, muscles need more blood flow, which reduces the amount of blood available to flow to the skin and release the heat.

Sweating also helps the body to cool off, but only when the humidity levels are low enough to allow the sweat to evaporate and if water and salts lost through sweating are replaced.

Heat Stress Disorders

When the body becomes overheated, a condition of heat stress exists. Heat stress can lead to a number of problems, including heat exhaustion, heat stroke, heat cramps, fainting, or heat rash. Many people confuse these disorders, but it is important to be able to recognize each one and know what to do when it happens.  Each of these heat stress disorders is described below.

Heat Exhaustion

Although not the most serious health problem, heat exhaustion is the most common heat-related ailment at Princeton University. Heat exhaustion happens when a worker sweats a lot and does not drink enough fluids or take in enough salt or both. The simple way to describe the worker is wet, white and weak.

Signs and symptoms

  • sweaty
  • weak or tired, possibly giddy
  • nausea
  • normal or slightly higher body temperature
  • pale, clammy skin (sometimes flushed)

What to do

  • rest in a cool place
  • drink an electrolyte solution, such as Gatorade or another sports drink.  Avoid caffeinated beverages such as colas, iced tea or coffee.
  • in severe cases involving vomiting or fainting, call Public Safety and have the worker taken to McCosh Health Center or Penn Medicine Princeton Medical Center, as appropriate.

Heat Stroke

Heat stroke is the most serious health problem for people working in the heat, but is not very common. It is caused by the failure of the body to regulate its core temperature. Sweating stops and the body can not get rid of excess heat. Victims will die unless they receive proper treatment promptly.

Signs and symptoms

  • mental confusion, delirium, fainting, or seizures
  • body temperature of 106ºF or higher
  • hot, dry skin, usually red or bluish color

What to do:

  • call Public Safety at 9-1-1 immediately and request an ambulance
  • move victim to a cool area
  • soak the victim with cool water
  • fan the victim vigorously to increase cooling

Heat Cramps

Heat cramps are painful muscle spasms. They occur when a worker drinks a lot of water, but does not replace salts lost from sweating. Tired muscles – those used for performing the work – are usually the most likely to have the cramps.

Signs and symptoms:

  • cramping or spasms of muscles
  • may occur during or after the work

What to do

  • drink an electrolyte solution (sports drink) such as Gatorade
  • If the cramps are severe or not relieved by drinking a sports drink, seek medical attention from McCosh Health Center or Penn Medicine Princeton Medical Center, as appropriate.

Fainting (heat syncope)

Fainting usually happens to someone who is not used to working in the hot environment and simply stands around. Moving around, rather than standing still, will usually reduce the likelihood of fainting.

Signs and symptoms

  • brief loss of consciousness
  • sweaty skin, normal body temperature
  • no signs of heat stroke or heat exhaustion

What to do:

  • lie down in a cool place
  • seek medical attention if not recovered after brief period of lying down

Heat Rash

Heat rash, also called prickly heat, may occur in hot and humid environments where sweat cannot evaporate easily. When the rash covers a large area or if it becomes infected, it may become very uncomfortable. Heat rash may be prevented by resting in a cool place and allowing the skin to dry.

Signs and symptoms

  • rash characterized by small pink or red bumps
  • irritation or prickly sensation
  • itching

What to do

  • keep skin clean and dry to prevent infection
  • wear loose cotton clothing
  • cool baths and air conditioning are very helpful
  • some over-the counter lotions may help ease pain and itching

Preventing Heat Stress

In most cases, heat stress can be prevented or, at least, the risk of developing heat stress can be reduced.

Engineering Controls

A number of engineering controls can help reduce heat exposure. These include:

  • general and local exhaust ventilation in areas of high heat
  • shielding of radiant heat sources, such as furnaces or hot machinery
  • elimination of steam leaks
  • use of cooling fans or personal cooling devices, such as cooling vests
  • use of power tools to reduce manual labor

Work Practices

  • Clothing:  Wear loose-fitting, lightweight clothing, such as cotton, to allow sweat to evaporate. Light colors absorb less heat than dark colors. When working outside, wear a lightweight hat with a good brim to keep the sun off your head and face.
  • Drinking:  Drink plenty of liquids, especially if your urine is dark yellow, to replace the fluids you lose from sweating – as much as one quart per hour may be necessary. Water and/or sports drinks are recommended. Since caffeine is a diuretic (makes you urinate more), beverage such as cola, iced tea and coffee should be avoided. Thirst is not a reliable sign that your body needs fluids. When doing heavy work, it is better to sip rather than gulp the liquids.
  • Work Schedule: If possible, heavy work should be scheduled during the cooler parts of the day. Otherwise, alternate heavy work in the heat with lighter work or work in cooler areas. When the temperature humidity index (see next page) is between 84 and 93 (Warning Zone), try to minimize the amount of time working in the heat such that approximately half of each hour is spent doing heavy work in the heat. When the temperature humidity index is 94 or higher (Danger Zone), this should be further minimized to approximately one quarter of each hour spent doing heavy work in the extreme heat.
  • Acclimatization:  New employees and workers returning from an absence of two weeks or more should have 5 days to get used to the heat. Begin with 50 percent of the normal workload and time exposure the first day and gradually build up to 100 percent on the fifth day.
  • Body Weighing: Workers may be at greater risk of heat stress if they lose more than 1.5% of their body weight in a single day from sweating.

Personal Protective Equipment

When work must proceed in hot conditions at Princeton, personal cooling systems may help reduce the risk of heat stress. There are several systems available through health and safety catalogs, including the following:

  • Heat reflective clothing may alleviate the problem of radiant heat sources, such as furnaces. However, if the worker is fully covered, he or she will have trouble evaporating sweat.
  • Ice vests or cooling vests remove heat from the skin. They are relatively inexpensive and allow freedom of movement.
  • Liquid cooling systems also remove heat from the skin. Cool liquid flows in the suit around the body and carries the heat away.


Employees and supervisors need to be trained to be able to detect early signs of heat stress. Employees must understand the need to replace fluids and salt from sweat and recognize the signs of dehydration, fainting, heat cramps, heat exhaustion, and heat stroke.

Supervisors should watch for signs of heat stress and allow workers to interrupt their work if they are extremely uncomfortable. Supervisors should also ensure that work schedules allow appropriate rest periods and ensure liquids are available. They should use appropriate engineering controls, personal protective equipment and work practices to reduce the risk of heat stress.



Cold Stress Facts

When working outdoors in cold weather or working in artificially cold environments, such as refrigerated areas, serious cold-related injuries and illnesses may occur.  Cold related hazards can cause permanent tissue damage or even death.

How cold is too cold?

When most people think of hypothermia, they think of frigid temperatures or blizzard like conditions.  Actually, hypothermia occurs most often in the spring and fall, rather than winter.

Four factors contribute to cold stress: cold temperatures, high or cold wind, dampness and cold water.  A cold environment forces the body to work harder to maintain its core temperature of 98.6oF.  Cold air, water, and snow all draw heat from the body. So, while it is obvious that below freezing conditions combined with inadequate clothing could bring about cold stress, it is important to understand that it can also be brought about by temperatures in the 50's coupled with rain and/or wind.

Wind chill is the combination of air temperature and air movement.  The higher the wind speed and the lower the temperature in the work environment, the greater the danger.  If weather information is not available, the following signs may help to estimate wind speeds in the field:

  • 5 mph: light flag just moves
  • 10 mph: light flag is fully extended by wind
  • 15 mph: raises a newspaper sheet off the ground
  • 20 mph: wind capable of blowing snow

How your body reacts to cold conditions

When in a cold environment, most of your body's energy is used to keep your internal temperature warm.  Over time, your body will begin to shift blood flow from your extremities (hands, feet, arms, and legs) and outer skin to the core (chest and abdomen).  This allows exposed skin and the extremities to cool rapidly and increases the risk of frostbite.  When the body can no longer maintain core temperature by constricting blood vessels, it shivers to increase heat production.  Maximum severe shivering develops when the body temperature has fallen to 95oF.  Hypothermia becomes an issue at this point.

Cold-Related Illnesses

Hypothermia means "low heat" and is a potentially serious health condition.  It occurs when body heat is lost from being in a cold environment faster than it can be replaced.  Symptoms begin with shivering.  As the body temperature continues to fall, slurred speech, lack of coordination and memory loss develop and shivering ceases.  Once the body temperature falls to around 85° F, the person may become unconscious, and at 78°, the person could die.

Risk Factors
Anyone working in a cold environment may be at risk for hypothermia.  However, older people may be at more risk than younger adults, since older people are not able to generate heat or regulate body temperature as quickly.

Certain medications may prevent the body from generating heat normally.  These include anti-depressants, sedatives, tranquilizers and some heart medications.

Signs and symptoms

Mild hypothermia (98 - 90° F)

  • shivering
  • lack of coordination, stumbling, fumbling hands
  • slurred speech
  • pale, cold skin

Moderate hypothermia (90 - 86° F)

  • shivering stops
  • mental confusion or impairment
  • reduced breathing and/or heartrate
  • unable to walk or stand
  • confused and irrational

Severe hypothermia (86 - 78° F)

  • severe muscle stiffness
  • very sleepy or unconscious
  • extremely cold skin
  • irregular or difficult to find pulse

First Aid
Proper treatment depends on the severity of the hypothermia.

Mild hypothermia

  • move to warm area
  • stay active
  • remove wet clothes and replace with dry clothes or blankets, cover the head
  • drink warm (not hot) sugary drinks such as sports drinks.  Avoid caffeinated beverages and alcohol.

Moderate hypothermia
All of the above, plus

  • Call 911 from a campus phone or 609-258-3333 from a cell phone for an ambulance
  • Cover all extremities completely
  • Place warm objects, such as hot packs or water bottles on the victim's head, neck, chest and groin

Severe hypothermia

  • Call 911 from a campus phone or 609-258-3333 from a cell phone for an ambulance
  • Handle the victim carefully.  Sudden movement or rough handling can upset heart rhythms.
  • Do not attempt to re-warm -- the victim should receive treatment in a hospital

Frostbite occurs when layers of skin tissue freeze.  In severe cases, amputation of the frostbitten area may be required. Frostbite can be caused by exposure to severe cold or by contact with extremely cold objects.  In fact, frostbite occurs more readily from touching cold metal objects because heat is rapidly transferred from skin to metal.

Frostbite typically affects the extremities, particularly the face, ears, fingers and toes.  Initial symptoms vary, but typically include skin that looks waxy and feels numb.  Once damaged, tissues will always be more susceptible to frostbite in the future.

Signs and symptoms

  • Cold, tingling, stinging or aching feeling in the frostbitten area, followed by numbness
  • Skin color turns red, then purple, then white or very pale skin, cold to the touch
  • Hard or blistering skin in severe cases

First Aid

  • Call Public Safety at 911from a campus phone or 609-258-3333 from a cell phone for an ambulance
  • DO NOT rub the area
  • Wrap in soft cloth
  • If help is delayed, immerse in warm, not hot, water.  Don’t pour water directly on the affected area because it will warm the tissue too fast.  Warming should take about 25-40 minutes.
  • Do not warm the skin if there is a chance of refreezing.  Severe tissue damage can occur.

Trench foot
Trench foot or immersion foot is caused by having feet immersed in cold water for long periods of time.  It is similar to frostbite, but considered less severe.

Signs and symptoms:

  • Tingling, itching or burning sensation
  • Blisters

What to do

  • Soak feet in warm water, then wrap with dry cloth bandages
  • Drink a warm, sugary drink

Preventing Cold Stress

Planning for work in cold weather is the most important defense.  Wearing appropriate clothing and being aware of how your body is reacting to the cold are important to preventing cold stress.  Avoiding alcohol, certain medications and smoking can also help to minimize the risk.

Protective Clothing
Wearing the right clothing is the most important way to avoid cold stress.  The type of fabric also makes a difference.  Cotton loses its insulation value when it becomes wet.  Wool, on the other hand, retains its insulative qualities even when wet.  The following are recommendations for working in cold environments:

  • Wear at least three layers of clothing:
    • An outer layer to break the wind and allow some ventilation (like Gortex® or nylon)
    • A middle layer of down or wool to absorb sweat and provide insulation even when wet
    • An inner layer of synthetic weave to allow ventilation
  • Wear a hat.  Up to 40% of body heat can be lost when the head is left exposed.
  • Wear insulated boots or other footwear sized appropriately.  Tight-fitting footwear restricts blood flow, as can wearing too many socks.
  • Wear insulated gloves sized appropriately, especially when contacting metallic surfaces and tool handles.
  • If you get hot while working, open your jacket, but keep hats and gloves on.
  • Keep a change of dry clothing available in case work clothes become wet.
  • Do not wear tight clothing which can restrict blood flow.  Loose clothing allows better ventilation.

Work Practices

  • Drinking:  Drink plenty of liquids, avoiding caffeine and alcohol.  It is easy to become dehydrated in cold weather.
  • Work Schedule: If possible, heavy work should be scheduled during the warmer parts of the day.  Take breaks out of the cold.
  • Buddy System: Try to work in pairs to keep an eye on each other and watch for signs of cold stress.  Victims of hypothermia may not recognize symptoms.

Engineering Controls
Some engineering controls are available to reduce the risk of cold stress:

  • Radiant heaters may be used to warm workers
  • Shield work areas from drafts or wind
  • Use insulating material on equipment handles when temperatures drop below 30° F.

Employees and supervisors need to be trained to be able to detect early signs of cold stress. Supervisors should watch for signs of cold stress and allow workers to interrupt their work if they are extremely uncomfortable.  Supervisors should also ensure that work schedules allow appropriate rest periods and ensure liquids are available.  They should use appropriate engineering controls, personal protective equipment and work practices to reduce the risk of cold stress.