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The Impact of Heat Stress in Firefighter Fatalities

Part 1. What is Heat Stress?

Firefighting is widely recognized as hard, dangerous work. But not only because of burns caused by blazing fires, but also because of exposure to extreme heat and high temperatures during strenuous physical activity.

Sudden cardiac events account for approximately 45% of firefighter duty-related deaths in the US each year. This is the highest mortal occupational cardiovascular disease of any professional group, according to the National Institute of Health.

Moreover, for every fatal on-duty heart disease event, there are about 17 nonfatal, cardiovascular events in the US fire service, research shows. Major fire departments experience as many as 12 to 20 chest pain or cardiac hospitalizations per 1,000 persons, every year.

What is the main cause of these health problems?

To find a solution to this problem, we need first to understand what heat stress is and how it affects firefighters. So, here is a deep dive into basic heat stress concepts, causes, and symptoms and consequences for firefighters’ health and safety.

How does heat stress lead to cardiovascular strain?

Heat stress, the main cause of firefighters’ line-of-duty fatalities and work-related diseases, is a condition determined by an excessively high temperature that the body cannot tolerate without suffering physiological impairment. Too much heat may cause headaches, vertigo, and unconsciousness and even death-provoking heat strokes.

Operations that rise workers' deep core temperature higher than 100.4 degrees F (38°C) present a risk of heat stress, according to the Occupational Safety and Health Administration (OSHA)‘s heat stress statistics.

The most common heat stress causes are:

- high air temperatures

- radiant heat sources

- high humidity

- direct physical contact with hot objects

- strenuous physical activities.

Firefighters can be exposed to up to 12.5 kW m− 2 and up to 300 °C temperature for a few minutes before heat stress disorders occur, according to sciencedirect.com. Heat exposure in a fire consists primarily of radiation, but convective and conductive heat (if, for example, molten metal or hot paint falls on a garment) may also be encountered.  

A firefighter’s core body temperature remains high, hours after exposure to fire. As a result, the blood becomes thicker, and blood vessels become potentially susceptible to harmful clots that impede normal blood circulation. This, along with environmental stress and dehydration, increases the risk of heart disease and sudden cardiac events.

According to the National Fire Protection Association (NFPA) heat stress statistics, in 2016 alone, there were 2,475 reported thermal stress injuries among firefighters.

When natural protection fails

Normally, when dealing with heat, the human body cools itself through body vessel dilation, which determines perspiration release. Sweat evaporates from the surface of the skin to lower body temperature, thus, avoiding overheating.

For firefighters, sweat evaporation cooling is inefficient. Insulated and enclosed personal protective equipment (PPE) inhibits normal thermoregulation during physical exertion. Insulation is a key feature of most turnout gear ensembles, ensuring that extreme heat stays away from the wearer. But it also keeps body heat trapped inside.

How to recognize heat stress disorders

Heat stroke is the most severe heat stress disorder. It happens when the body’s autoregulation function fails, and the temperature rises to critical levels. It is a medical emergency that may result in death.

Heat stroke is fatal in up to 80% of cases.

The first symptoms of heat stroke are confusion, irrational behavior, loss of consciousness, convulsions, a lack of sweating, hot, dry skin, and abnormally high body temperature. Heat stroke is caused by a combination of variable factors such as workload and environmental heat; therefore, this condition is hard to predict. At the first signs of a heat stroke, professional medical treatment should be sought immediately.

Heat exhaustion is easily recognizable by symptoms such as headache, nausea, vertigo, weakness, thirst, and giddiness. Although a severe condition, it responds to correct treatment. Several heat stress disorders such as fainting, or heat collapse are often mistaken for heat exhaustion, but the difference is that these do not affect the body's heat balance. The danger comes from the fact that workers who lose consciousness may be injured fainting.

Heat cramps are muscle spasms localized in the abdomen, arms, and calves, and they occur while performing hard physical labor in a hot environment. Heat cramps are attributed to an electrolyte imbalance caused by sweating and appear to be caused by the lack of water replenishment. If the firefighter doesn’t hydrate properly, the water lost through sweating will not be replaced, excess salt building up in the body, as sweat is a hypotonic solution (±0.3% NaCl).

Under extreme conditions, such as working for 6 to 8 hours in heavy protective gear, a loss of sodium may occur. In such situations, carbohydrate-electrolyte replacement liquids are effective in minimizing physiological disturbances during recovery. For prevention, water must be taken every 15 to 20 minutes in hot environments, no matter if thirsty or not.

Heat stress rash is the most common problem for firefighters. It appears in hot work environments and is caused by unevaporated sweat that leaves skin persistently wetted.

Heat stress rash manifests as red papules produce an itching sensation and it usually appears in areas where the clothing is restrictive. If not treated, papules may become infected. However, in most cases, they disappear in a cool environment.

Heat fatigue is a condition caused by a lack of acclimatization. The signs and symptoms are usually related to impaired performance of skilled manual, mental, or vigilance jobs. Heat stress can be prevented with acclimatization programs and training in hot environments. However, there is no treatment for it except removing heat stress before a more severe condition develops.

The good news is that all these heat-related illnesses can be prevented. Our next article with cover heat stress management techniques for firefighters, including new turnout gear innovations. Stay tuned!