When the human body’s thermoregulatory functions are unable to maintain heat balance in a hot environment, any of several maladies may result. Collectively known as “heat illness,” these maladies vary widely in severity. Therefore, a generic diagnosis of heat illness may provide insufficient information to assess future risks to individuals and populations or to develop effective management plans.
This installment of the “Thermal Work Environments” series describes the range of heat illnesses that workers may experience. This information can be used to identify risk factors and develop preventive measures. It also facilitates effective monitoring of conditions, recognition of symptoms, and proper treatment of heat-effected employees.
The following descriptions of heat-related illnesses are presented in order of increasing severity, though individual sensitivities and proclivities renders this sequence an approximation. Also, it should not be assumed that these illnesses will always be experienced in the same way. For some, symptoms of lower-level illness may not be present, or detectable, prior to onset of more-severe heat illness. However, when symptoms of “minor” illness do appear, they must be given prompt attention to prevent the person’s physical condition from degrading further.
While not truly a heat illness itself, the initial discomfort experienced due to heat is the first warning sign of impending heat stress and that management of the thermal environment may be necessary. Although a person’s experience does not always reflect a clear progression of effects, warm discomfort is a likely predecessor to subsequent heat illness.
Although dehydration can occur in any environmental conditions, it is most-often associated with heat stress. Elevated temperature accelerates fluid loss; a demanding work cycle can limit a person’s opportunities to rehydrate or his/her conscious awareness of the need. These demands exacerbate physical conditions that may exist upon entering the work environment. Specifically, beginning work with a suboptimal hydration level (i.e. hypohydration) increases a worker’s risk of severe dehydration or heat illness.
Sometimes called “prickly heat,” heat rash is a common occurrence in hot work environments; it occurs during profuse sweating. It is caused by sweat ducts becoming blocked, forcing sweat into surrounding tissue. It is characterized by clusters of small blisters that give the skin a bumpy, red, or pimply, appearance. It appears most often on the neck, upper chest, and anywhere that skin touches itself, such as elbow joint creases, or where excretion of sweat is otherwise restricted.
Dismissing heat rash as an aesthetic affliction is a mistake. It is an indication that thermoregulatory function has been inhibited to some degree and should not be ignored. Unchecked, it could accelerate onset of more-severe heat illness.
The most effective response to heat rash is to move to a cooler, less humid environment. Unfortunately, this is not often a realistic option. Therefore, the person’s overall condition should be monitored to prevent worsening illness. The area of the rash should be kept dry; powder may be applied for comfort, but anything that warms or moistens the skin should be avoided.
Uncontrolled contractions or spasms, usually in the legs or arms, often result from the loss of fluid or salts when sweating. Strong, painful muscle contractions are possible, even when a person has been drinking water. If body salts, such as sodium and potassium, are depleted without replenishment, heat cramps are often the result.
To offset the effects of profuse sweating, electrolyte-replacement drinks (i.e. “sports drinks”) should be added to the hydration regimen. Eating an occasional snack is an alternate method of salt replenishment that may better serve a worker’s energy requirements than liquids alone.
Syncope is the occurrence of dizziness, lightheadedness, or fainting. Onset is usually caused by standing for an extended period of time or suddenly rising from a seated or prone position. Dehydration and lack of acclimation to the hot environment may be contributing factors to the occurrence of heat syncope.
It may be reasonable to address the heat-related illnesses previously discussed without medical attention beyond the assistance provided by coworkers. A case of heat exhaustion, however, warrants professional medical care to ensure proper treatment and recovery.
Heat exhaustion is caused by extreme dehydration and loss of body salts. It is characterized by several possible symptoms, including headache, nausea, thirst, irritability, confusion, weakness, and body temperature exceeding 100.4° F (38° C).
First aid for heat exhaustion includes moving the person to a cooler environment and encouraging him/her to take frequent sips of cool water. Apply cold compresses to the person’s head, neck, and face; if cold compresses are not available, rinse the same areas with cold water. Unnecessary clothing, including shoes and socks, should be removed; this is particularly important if the person wears impermeable protective layers, such as a chemical-resistant smock, leather garment or boots, etc. At least one person should stay with the stricken worker, continuing the actions described, until s/he is placed in the care of medical professionals. At such time, provide all pertinent information to expedite effective treatment.
Protracted physical exertion under heat stress can cause muscles to break down, releasing electrolytes, primarily potassium, and proteins into the bloodstream. An elevated level of potassium can cause dangerous heart rhythms and seizures and large protein molecules can cause kidney damage.
Symptoms of rhabdomyolysis include muscle pain and cramps, swelling, weakness, reduced range of motion, and dark urine. There is an elevated risk of misdiagnosis due to the similarity of the commonly-experienced symptoms to those of less-severe afflictions. Tests can be performed to ensure proper diagnosis and reduce the risk of future complications.
Acute Kidney Injury
One cause of kidney damage, as mentioned above, is the release of proteins from muscles that the kidneys are unable to process effectively. It may also occur as a result of prolonged heavy sweating. Low fluid and sodium levels (hypohydration and hyponatremia, respectively) impede normal renal function. Unresolved, this can lead to kidney failure and the need for dialysis. An effective hydration regimen is critical to kidney health.
When the body’s thermoregulatory functions can no longer manage the heat stress to which it is subjected, heat stroke is the ultimate result. Onset of heat stroke is typically characterized by hot, dry skin and body temperature exceeding 104° F (40° C). The victim may also be confused or disoriented, slur speech, or lose consciousness. Rapid, shallow breathing and seizures are also potential symptoms of heat stroke.
Two types of heat stroke are possible: classic and exertional. The two are differentiated by several factors, summarized in Exhibit 1. The key distinction is that classic heat stroke occurs during activity of much lower intensity than that inducing exertional heat stroke. Sweating often continues during exertional heat stroke, eliminating an easily-identifiable symptom and potentially causing dangerous underestimation of the severity of a victim’s condition.
First aid for both types of heat stroke is very similar to that for heat exhaustion, though more aggressive. Additional cold compresses should be applied, particularly to the armpits and groin. More thorough soaking with cold water, or in an ice bath, with increased air movement, should be provided to the extent possible. Emergency medical care is a necessity for every heat stroke victim.
Undiagnosed or untreated heat illness can escalate rapidly. Ignoring early warning signs places all workers in a hot environment at greater risk of heat stroke or other serious injury. With a mortality rate of ~80%, heat stroke victims require immediate attention to have any hope of recovery; a body temperature exceeding 110° F (43.3° C) is almost always fatal.
Hot environments pose a greater risk to life than do cold environments. There are three key reasons for this:
Other Heat-Related Effects
There are risks associated with hot work environments that are not adequately described in the “traditional” sense of heat illness. A workplace with a radiant heat source (other than the sun) places workers at risk of burns. The source of radiant heat is a hot object, often a furnace, forge, or other process equipment. Workers may be required to be in close proximity to such equipment to operate or interact with it, such as when loading or unloading material. A small misstep could cause a person to come in contact with the equipment or heated material. Even with protective gear in proper use, direct contact could result in a severe burn.
Thus far, the afflictions discussed have been physical in nature. However, there are also heat-related cognitive effects to consider. Tests conducted on subjects under heat stress have demonstrated the potential for significant cognitive impairment during extended exposure.
Test subjects experienced reductions in working memory and information-processing capability. Other results showed that stimulus-response times and error rates increased, with a subsequent increase in total task time. Performance of complex tasks was effected to a greater degree than simple tasks, suggesting that subjects’ ability to concentrate had been negatively impacted by prolonged heat stress.
The potential effect on productivity and quality of impaired task performance is easy to infer. Less obvious, perhaps, is the increased risk of injury that results from reduced information-processing capability and increased reaction time. Any lag in recognizing a dangerous condition, formulating an appropriate response, and executing it significantly increases risk to personnel and property.
Discussion of each of the heat-related illnesses and other effects has implicitly referenced the time during a work shift. The time between work shifts is also critically important to the well-being of workers returning to a hot environment day after day.
The duration of the gap between shifts and the activities in which a person engages during that time determine his/her condition at the beginning of the next shift. For optimum health and performance in subsequent shifts, workers should consider the following recovery plan elements:
Workers in hot environments are exposed to a number of risk factors for heat-related illness. The diagram in Exhibit 2 names a baker’s dozen of them; several have already been discussed in this series. For example, the presentation of the heat balance equation in Part 2 included discussion of several of these factors, including temperature and humidity, radiant heat sources, physical exertion, and medications. Others are discussed further in subsequent installments of the “Thermal Work Environments” series.
The effects of heat stress range from mild to severe, even fatal. Protection from heat illness begins with a cohesive team, whose members look after one another and respond appropriately to the earliest signs of onset. To be effective guardians of their own health and that of their teammates, workers must possess an understanding of heat illness, common symptoms, and first aid treatments. Tolerance to heat varies widely among individuals; the ability to recognize changes in a person’s condition or behavior, in the absence of sophisticated monitoring systems, is paramount.
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For a directory of “Thermal Work Environments” entries on “The Third Degree,” see Part 1: An Introduction to Biometeorology and Job Design (17May2023).
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Jody W. Phelps, MSc, PMP®, MBA
JayWink Solutions, LLC
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