A firefighter needs to evaporate about 1 litre of sweat per hour to be able to regulate their body temperature when being exposed to extreme heat.* The human body is designed to function within a very specific temperature range – between 36.5 and 37.5°C. However, fighting fires tests these limits and can increase a firefighter’s body temperature to over 38 degrees. It is little wonder then as to why heat stress is such a ‘hot’ topic in the industry.

Here, Nathan Bricknell, general manager at FlamePro, a British specialist manufacturer of life-saving garments for firefighters, explains more about heat stress and other heat-related risks, and what to take into consideration when purchasing structural firefighter gear to help reduce the danger.

What is heat stress?

Heat stress occurs when the human body cannot get rid of excess heat. When this starts to happen, the body’s core temperature will begin to rise and the heart rate increases. As the body continues to store heat, the person begins to lose concentration and will have difficulty focusing on a task. They may also become irritable or sick, and will often lose the desire to drink, which will only worsen their condition.

Heat stress, unsurprisingly, puts firefighters at greater risk of developing heat-related illness. These illnesses can cause a range of symptoms, from cramps or fainting, to possible risk of heart attack and even death if the person is not cooled down.

Types of heat illnesses in firefighters

Electrolyte imbalances can occur from excessive fluid loss or excessive loss of salts through sweating, both of which are common problems for firefighters. This can cause a number of heat-related illnesses, including heat cramps, heat exhaustion and heat stroke.

• Heat cramps are short, severe muscle spasms which occur during heavy exercise in hot environments, such as the environments that firefighters are regularly exposed to. These cramps often happen in the leg, arm or abdomen, and are caused by heavy sweating using up the body’s supply of salts. This can obviously have an impact on a firefighter’s ability to do their job effectively and safely.
• Heat exhaustion occurs when firefighters are exposed to high temperatures, particularly when combined with high humidity, and strenuous physical activity. Symptoms can include extreme thirst, fatigue, weakness, clammy skin, nausea or vomiting, and rapid breathing. Heat exhaustion is not usually serious, if the firefighter can cool down within 30 minutes. However, after this, heat exhaustion can then develop into heat stroke, which is a medical emergency.
• Heat stroke is the most serious heat-related illness, and left untreated for even a short time, can cause death. Heat stroke occurs when body temperature rises too rapidly within 10 to 15 minutes. The typical symptoms include red, hot and dry skin, altered mental status or loss of consciousness, and rapid, weak pulse. However, it’s worth noting that a firefighter who suffers a heat-stroke attack while wearing their fire suit may not present with the typical hot and dry skin with no visible sweating that you would expect from heat stroke. This is because some traditional fire suits retain heat and moisture and prevent it from evaporating, meaning the firefighter may instead present with moist, red skin, which is hot to the touch.

The risks of heat stress on a firefighter cannot be underestimated. Mild heat stress might start with your firefighting crews tiring more quickly, meaning it takes longer to get a fire under control, as it will leave them unable to work as quickly.

However, if left untreated, heat stress can lead to poor decision-making as cognitive function deteriorates, and massive pressure on the body’s natural functions, which can have serious or even deadly consequences.

While there are many factors to consider to reduce the impact of heat stress on firefighters – such as hydration and heat acclimatisation – a major component of heat stress control is the selection of Personal Protective Equipment (PPE). But knowing what to look for when specifying PPE for your brigade is crucial.

Insulation – friend or foe?

Insulation is an important part of any firefighter kit, as it keeps the extreme heat away from the wearer. However, it also keeps the body heat in.

We all know that sweating is the best way for our bodies to regulate their temperature, but for sweating to be effective, the air should be dry and moving, like when it’s windy.

When it’s humid there is less capacity within the air for vapour to leave your body and that makes sweating less effective. An enclosed and insulated fire suit without airflow doesn’t promote the ideal perspiration environment.

The incredibly demanding job and the body heat a firefighter creates is unavoidable, therefore the challenge is finding a way to get the heat out of their suits without letting heat from the outside in. This is where moisture barriers play a crucial role in reducing the chance of heat stress.

Moisture barriers

A moisture barrier is an exceptionally clever type of material that lets vapour through and in some cases liquid (unidirectionally), making a suit breathable and allowing the wearer to sweat away the heat, all without letting water, harmful chemicals or pathogens in. When it comes to fire suits, this moisture barrier plays an important role in regulating body heat as it allows as much moisture vapour out as possible.

However, all moisture barriers are not ideally suited for structural suits. You can imagine how uncomfortable getting the balance and selection wrong can be for your firefighters in the heat of a fire. A good moisture barrier is designed to be breathable, comfortable, and to let vapour through, but not liquid.

There are three types of moisture barrier product technology used in fire fighters’ protective garments: microporous, monolithic, or bi-component. A microporous membrane allows for the most air permeability, as it contains small passages or holes, which offers water vapour transfer by air-diffusion.

Good mobility promotes efficient suits

It’s important that fire suits are designed to be wearer friendly, whilst providing optimum protection. When selecting the right gear, consider how easy the suits are to move in and how they operate with the body to help airflow, reduce moisture retention and aid cooling, and bear in mind the different requirements of your team.

PPE that is designed to provide increased mobility helps to reduce muscular strain, improves air circulation and in turn minimises heat stress.

Airflow is a crucial factor when sizing, and suits should be slightly larger than firefighters might expect. The air gap between skin and suit is a crucial component in heat protection and prevention of heat stress. The hot air needs to be able to move around, away from hotspots like the shoulders, and ultimately out of the suit in order to minimise the danger.

Treating heat stress

While prevention is key to ensuring firefighters’ safety, it’s also important to be familiar with necessary steps to treat heat stress at its various stages, should any heat-related illnesses begin to set in. These include:

Treating heat cramps:

• Stop all activity, remove all items of PPE, particularly the protective hood, and sit in a cool place.
• Drink water, a sports drink, or another cool drink with no caffeine or alcohol.
• Seek medical help if the cramps have not stopped within one hour.

Treating heat exhaustion:

• Again, stop all activity, remove all items of PPE, particularly the protective hood, and sit in a cool place.
• Drink water, a sports drink, or another cool drink with no caffeine or alcohol.
• Sit in front of a fan to help promote sweat evaporation and cool the body.

Heat stroke is a time-critical emergency and you should call for medical assistance immediately, should an attack occur. While you wait for assistance, you should do the following:

• Get the firefighter into a shady/cool area.
• Cool them as quickly as possible with cold water immersion (cryotherapy). This is where you place the firefighter in a tub with ice and cold water, stirring the water and adding ice throughout cooling process (making sure to protect their airway throughout this process). If this is not possible, spray the firefighter with cold water from a hose, or keep them wrapped in a cold, wet sheet.
• Check their body temperature often and continue your cooling efforts until their temperature has dropped.
• Do not give any fluids to drink until their body temperature has lowered.

For more information, go to www.flame-pro.com

*Data from https://www.fs.fed.us/eng/pubs/htmlpubs/htm99512841/page11.htm