Heat Stroke: A Case Study

Heat Stroke: A Case Study

An ever-increasing percentage of the U.S. economy relies on unsung heroes who physically move products we buy. According to a 2024 Government Accountability Office study, workers in warehouses, on loading docks, and delivering packages have higher rates of workplace injury than in any other major private industry sector. While many injuries occur from heavy lifting or repetitive strain, heat illness is an escalating threat, particularly in locations like sprawling, often poorly cooled warehouses.

This article is the first in a two-part series on heat and labor. In this first article, we follow a fictional warehouse employee (we’ll call him Jake) through a workday ending abruptly with heat stroke. Along the way, we explore the science behind the occupational and personal risk factors that contribute to Jake’s heat stroke emergency.

Meet Jake

Our protagonist, Jake, is a new employee starting his first week on the warehouse floor. He’s in his mid-20s and relatively healthy. Young and without chronic medical conditions, he doesn’t have two big personal heat stroke risk factors: advanced age and prescription medication use.

Personal Factor 1: Age

No single organ responsible for the body’s thermoregulation. Maintaining a stable body temperature requires nearly all the body’s systems working together. As we age, some physiological systems degraded, affecting our overall ability to cool off in the heat. In his mid-20’s, Jake doesn’t yet have to worry about age affecting his ability to thermoregulate. Declines in human thermoregulatory performance begin around age 50 and are especially dangerous in elderly people, who have less sensitive thermoreceptors.

Personal Factor 2: Medication

Being young and healthy, Jake also doesn’t have to worry about the effects of medication on thermoregulation. Many common blood pressure medications are diuretic, meaning they decrease blood volume. While useful for lowering blood pressure, that’s not great for thermoregulation; blood is, functionally, the body’s equivalent to radiator coolant. In addition to increasing the risk of dehydration, reduced blood volume means less blood available to shuttle heat away from internal organs.  

Other medications reduce the body’s ability to sweat and can elevate core temperature. Drugs such as antidepressants that affect the hypothalamus (an area of the brain that, among other things, regulates core temperature) can prevent thermoregulatory responses from kicking in when needed. An analogy is a working A/C system with an mis-calibrated thermostat reading a wrong, cooler, temperature- the “set point” to initiate cooling is mistakenly too high.

Personal Factor 3: Jake’s Cold

Although Jake doesn’t have chronic medical conditions, he has a slight viral infection- annoying, but not enough to make him call out sick during his first week. This is problematic because infection and heat stress both generate immune responses, with the combination potentially overwhelming the body’s system. To fight his cold, Jake’s body has naturally raised its core temperature by about 1.5^oF, giving him a mild fever of about 100^oF which he (temporarily) suppresses with Tylenol before work. By lunch the medicine will wear off, returning his baseline temperature to about 100^oF. This mild fever means Jake is already slightly hyperthermic even before his physically demanding job begins generating metabolic heat.

Morning – Buildup to Heat Exhaustion:

Personal Factor 4: Acclimatization

Starting his third day in the warehouse, Jake is a recent hire. His last job as a store clerk required nothing more physically demanding than standing at an air-conditioned cash register. His new job on the warehouse floor requires far more physical effort. On his third day, Jake is only now beginning to develop protective heat acclimatization adaptations that help protect the body from heat stroke.

Acclimatization, as discussed in this Qore Performance article, develops our body’s natural defenses against heat. It is among the most important protective factor against heat illness. Acclimatization benefits includeimproved cardiovascular function, more efficient sweating, and lower core temperature. However, full heat acclimatization requires about two weeks of dedicated exposure to heat. Recognizing that non-acclimatized workers are at greater risk of heat illness, the U.S. Center for Disease Control recommends new workers without experience in hot environments be exposed to heat for no more 20% of a shift on their first day, and not more than an additional 20% each subsequent day.

Personal Factor 5: Dehydration

Knowing he’ll be moving heavy packages around hot loading docks, Jake brought a gallon of water with him during his first two days. Unfortunately, this was only about half the amount needed to provide the approximately one liter he should be drinking every hour over his eight hour shift. Dehydrated, Jake starts his third day in the warehouse already experiencing significant declines in his ability to think and react. Dehydration can reduce performance of simple tasks by about 4%, and 16% for more complex tasks. Dehydration is also one of the leading risk factors for heat stroke.

Jake isn’t an outlier. Starting a workday dehydrated is common. A large European study across four countries and various occupations (manufacturing, construction, and law enforcement were included) found 23% of workers started their shift “severely” and “clinically” dehydrated, with just 22% optimally hydrated. U.S. studies of agricultural workers found nearly 97% of subjects ended their shift dehydrated, while a separate study of construction workers found 56% show up dehydrated at the start of a shift.

Occupational Factor 1: The Heatwave

Obviously, heat injuries are more likely during hot temperatures. Less well known is the effect of multiple hot days- such as during a heatwave- which are cumulative. Jake’s timing is unlucky, as his first day in the warehouse coincides with the start of a heatwave. According to one study, by the third day of temperatures above 92^oF, the odds of workplace injury increase by 15%. During very severe heatwaves, another studyputs the increased odds much higher, at 45%.

Overall, workers like Jake- young, male, inexperienced, and involved in physically demanding labor- are most likely to be injured during extreme heat. A large meta-study (over 22 million occupational injuries across six counties) found a 17.4% average increase in workplace injuries during heatwaves. Hiding in this data are differences between regions. Workers in humid subtropical climates, such as most of the Southeastern United States, average a 21% increase in workplace injuries during heatwaves.

Jake’s warehouse is air conditioned, but warehouses- voluminous metal box structures- are difficult to cooleffectively. With outdoor temperatures approaching 95^oF by lunch, the building’s climate control system struggles to keep up and the warehouse interior climbs above 80^oF.

Lunch Break – Heat Syncope:

By lunch, Jake is excessively tired and has a headache, early symptoms of heat illness. Standing after a short lunch break, he nearly falls when experiencing an acute episode of dizziness, or heat syncope.

Heat syncope, which can also include fainting, results from low blood pressure induced by heat stress. In an effort to shuttle heat from Jake’s brain and organs to the skin surface (where it can be released), his blood vessels dilate. The same volume of blood in now-wider blood vessels reduces pressure, making it harder for the heart to pump blood against gravity to elevated body parts like the brain. Fully hydrated, Jake may have avoided this bout of heat syncope, but his dehydrated state (compounded by heavy sweating all morning) has further reduced to his blood plasma volume.

Recovering from his dizzy spell, Jake heads to the loading dock. His cardiovascular system is now fighting to accomplish two increasingly contradictory goals with a diminished supply of blood plasma – provide his brain with enough blood to stay conscious while also diverting blood flow to his skin for thermoregulation. Attempting both, his heart rate spikes near 100 beats per minute, a condition known as tachycardia, even before unloading his first box of the afternoon.

Jake is lucky to be young and relatively healthy. Heat stress places a significant burden on the cardiac system, with heart attacks a leading cause of heat stress induced death in older adults. In fact, heart attack deaths spike nearly 12% during heatwaves.

Afternoon – Conditions for Heat Stroke:

Occupational Factor 2: The Humidity

By 1:00pm, Jake is at the loading dock working hard to empty several delayed trailers. The outdoor temperature touches 98^oF, and it’s humid. Warehouse temperatures near the loading dock are closer to 85^oF- cool only compared to outside- and Jake makes repeated trips into uncooled trailers to unload. After forty minutes of work, with his heart racing and a splitting headache, Jake feels weak and must sit for a quick break- he is experiencing heat exhaustion.

Momentarily dodging his supervisor, Jake half-sits, half-collapses near one of the large industrial fans near the loading docks. In most conditions fans help people cool because they increase convective and evaporative heat loss by replacing warm, moist air at the skin surface with cooler, dryer air blown by the fan. Unfortunately for Jake, fan effectiveness is limited in hot, humid conditions.

Most health agencies discourage fan use in temperatures above 95^oF (and sometimes even lower), especially for older folks, for reasons of basic physics. Heat flows from hot to cold, and skin temperature must be around 95^oF for a thermal gradient sufficient to offload body heat. A fan blowing air above 95^oF against the skin can add heat to the body.

The exact temperature-humidity combination where fans start adding heat to a person is complicated because of sweating. Sweating is our strongest natural cooling mechanism, so blowing hot (>95^oF) but dry air results in net body cooling if it promotes sweat evaporation. However, blowing hot, humid air that doesn’t greatly increase sweat evaporation rate can have the opposite of its intended effect, adding heat to the body.

It's likely the fan helped Jake cool off, but only slightly. For young, healthy adults, a study of conditions in 108 cities estimated, on average, fan use helps remove heat on all but the hottest 3% of days. Unfortunately for Jake, his supervisor notices him and promptly ends his unscheduled break.

The Physiological Limit Reached

Occupational Factor 3: Lack of Heat Safety Culture &

Occupational Factor 4: Physically Demanding Work

Events now become critical for Jake. Ideally, Jake’s supervisor would notice the warning signs of heat illness and take appropriate action. Such attention by foremen, shift supervisors, and crew leaders is becoming more common- and more important- as heatwaves last longer and become more intense.

Jake’s supervisor could have enforced well-established activity modification guidelines for working in the heat. Human muscles are inefficient, with most calories burned (around 75%) resulting in metabolic waste heat that must be offloaded. In general, the harder the work, the more metabolic heat produced – and the greater potential for heat stress.

In hot environments, “heavy work”, such as unloading trailers, should follow rest period recommendations that may significantly limit the duration of work performed . For example, the National Institute for Occupational Safety and Health recommends 40 minutes of rest for every 20 minutes of hard work on a humid 98^oF day. Such guidelines aren’t set for comfort (working in the heat is miserable from the start), but rather to limit a worker’s core temperature rise by periodically and temporarily reducing metabolic heat production.  

Work/rest guidelines from the National Institute for Occupational Safety and Health for a young, healthy worker like “Jake”. Note the “Adjusted temperature” is not ambient temperature; humidity and sun exposure add up to 9^oF and 13^oF, respectively, easily creating “adjusted temperatures” well above 100^oF in even relatively moderate temperature conditions.

Personal Factor 6: Motivation

A final risk factor now tips Jake into heat stroke territory – motivation. With his supervisor’s prompting, Jake heads back into the trailer for another box, determined not to be the new guy who “couldn’t handle it”. Many Western militaries follow heat stress guidelines that note the “most motivated soldiers” are particularly at risk of heat stroke because they are the ones most likely to physically overexert themselves to accomplish a task or mission.

Motivation can be the “tipping point” factor during heat stress. A report published in the Journal of Special Operations Medicine details five cases of heat stroke during U.S. Army training programs. In each, soldiers pushed beyond their physical limits to achieve specific tasks or goals, ignoring warning signs.

The Heat Stroke

Jake takes another three trips between loading dock and warehouse before collapsing. During this final push, his already-elevated core temperature rises rapidly, overwhelming his remaining thermoregulatory ability. Blood flow, already limited due to dehydration and cardiovascular strain, becomes insufficient to support both thermoregulation and brain function. With blood increasingly routed to his skin to offload heat, Jake becomes disoriented, then collapses, semi-conscious. His core temperature is now well above 104°F, the clinical threshold for heat stroke.

Jake now experiences the defining symptom of heat stroke- neurological (i.e., brain) impairment. He is confused and his speech is slurred. Given the brain’s sensitivity hyperthermia (i.e., high core temperature), brain malfunctioning is “inevitable in heatstroke” victims. Confused about where they are or what is happening, heat stroke victims may become combative. Often, neurological damage progresses to seizures, coma, and even death. Without rapid cooling, Jake risks long term brain damage.

Other body functions are also critically stressed, beginning a dangerous inflammatory cascade. During heat stroke the barrier between intestines and body begins to fail, allowing toxins to enter the bloodstream. Inflammatory cytokines (a type of protein that helps control inflammation) surge, leading to vascular damage, brain swelling, and disrupting cell functions. Muscle proteins break down, releasing myoglobin, which clogs kidneys, setting off acute renal (i.e., kidney) failure. The heart races to dangerous levels, significantly elevating the risk of heart attack. Jake now risks permanent damage to his heart, kidneys, liver, and cardiovascular system.

Resolution

Fortunately, a fellow warehouse worker notices Jake’s collapse and guesses the cause. Carrying Jake into a (relatively) cooler part of the warehouse, he douses Jake with ice-cold water from a cooler while an ambulance is called. Prompt cooling is vital for heat stroke victims- the longer core temperature remains elevated, the greater the chance for long term complications or death. If cooled within 30 minutes, survival rates approach 100%.  

Jake’s story shows how heat stroke is not a sudden, random event, but the result of multiple compounding physiological stressors: days of high ambient temperature, humidity, exertion, dehydration, inadequate acclimatization, and personal drive. These factors combined pushed Jake over the edge.

Preventing heat stroke cases like Jake’s requires active monitoring, rest cycles, hydration strategies, and a workplace safety culture that emphasizes understanding the signs of impending heat stroke. Heat Injury Prevention Solutions by Qore Performance help address the challenges of heat stress in the workplace. Qore Performance offers products, like wearable thermoregulation equipment to avoid heat injury and boost productivity on the warehouse floor and beyond.

---

About the author: Dr. Erik Patton holds a PhD from Duke University where he conducted research on the challenges rising temperatures pose for military training. An Army veteran, Erik has served in a variety of extreme climates ranging from deserts in the U.S. Southwest and Middle East (120^oF) to Arctic conditions in central Alaska (-42^oF).