Research team develops firefighter jacket with cooling system

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A research team from the University of Salzburg and Salzburg Research has developed a self-cooling firefighter jacket designed to protect firefighters from overheating. The commissioned work includes a sensor system that initiates countermeasures when a critical body temperature is reached.

The jacket itself primarily supports the body's own cooling process. Sweat can evaporate better on the skin when the humidity is low. The system is designed to achieve this by cooling the air.

Heat impairs decision-making ability

A problem is not only a possible physical collapse, but also the psychological influence: from a heat stress of 38.5 degrees Celsius core body temperature, people behave more riskily, more impulsively and tend to overestimate themselves physically.

"We want to find out whether the new type of air cooling actually improves the subjective well-being of firefighters, reduces physical stress and, if necessary, enables more considered decision-making under heat stress," says Jannic Wälde from the University of Salzburg.

Sensors measure humidity in the jacket

Although a compressed air bottle carried on board can only supply a limited amount of fresh cooling air, the cooling must still be effective. At the same time, the system has to withstand the extreme conditions of a firefighting operation, which was a particular challenge, explains Severin Bernhart from Salzburg Research, a research institute specializing in motion data analysis.

Sensors made from a cotton fabric with integrated conductive stainless-steel threads react to the humidity in the firefighting jacket- caused by sweat. "When the textile becomes damp, the resistance in the textile changes, which is measured via a 10kOhm voltage divider," explains Bernhart. The research team found that the humidity data from the sensor was related to the humidity in the jacket's microclimate. This in turn correlates with the wearer's core body temperature, explains the researcher. The laboratory study indicated that the sensor provided the most accurate data when it was placed on the upper back.

Practical test in the sauna

To test the system, 19 participants in an initial laboratory study were placed in a sauna wearing protective suits and masks. The test subjects then answered questions for a cognitive test while still in the equipment – after a running session on the treadmill including helmet and oxygen cylinder. This enabled the team to better differentiate between heat stress caused by heat and heat stress caused by physical exertion.

"From the laboratory data, a tipping point was identified at which the core body temperature rises sharply," says Bernhart. Based on the findings, the scientists developed an algorithm to estimate the tipping point. However, the calculated tipping point occurred too early in the test scenario. In the test, the researchers worked with a semi-automatic solution: a time barrier prevented it from being triggered too early. "Without this time barrier, the cooling would usually have triggered too early," says Bernhart. The reason for this: In the test, the participants were already sweating with the equipment before they went into the fire. There is therefore still room for improvement in the sensor technology and algorithm for real situations.

Fresh air reactivates the body's own cooling system

A signal from the sensors to the compressed air cylinder activates the system and brings fresh air under the jacket. "The fresh, dry air displaces the air saturated with sweat so that the body's cooling mechanism can function again and heat stress can be avoided if necessary," explains Bernhart.

The team tested the jacket prototype in a fire simulation facility. In a trial with twelve firefighters wearing the jacket and a control group, both the sensor data and the feedback from the participants showed that the system worked. The team is still evaluating whether the system also has an effect on core body temperature.

Bernhart and his colleagues can not yet estimate how expensive such a jacket could be. "Of course, we are trying to keep the integration of the system as simple as possible so that the costs are not too high," says Bernhart. "We are currently at the prototype stage and the comfort and usability of the product still need to be improved."

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