# Applicability of Human Thermophysiological Model for Prediction of Thermal Strain in PPE
## 2 Materials and Methods
### Testing of the Thermal Strain in Climatic Chamber  
The real tests of physiological strain were conducted in a climatic chamber of the National Institute for NBC Protection according to a standard protocol with up to 12 volunteer probands (6 men and 6 women) experienced in PPE testing in climatic chambers or familiar with using PPE at work. Anthropometric data (height, weight etc. ), the Body Mass Index (BMI), and other individual characteristics were measured for each proband before each test, and the VO\({}_{\text{2 max}}\) value was measured for each proband in advance of the set of tests as an indicator of physical fitness. Some of the probands were not able to conduct the complete set of tests within the research; therefore, the count of the tests under the same conditions may vary, as indicated in the Section 3. The tests of physiological strain under conditions of \(-10\)\({}^{\circ}\)C and \(5\)\({}^{\circ}\)C were not conducted with all probands, as these tests were performed only for informative reasons (testing of the applicability of the thermophysiological models), as these conditions are outside the validity range of the thermophysiological models; for the count of the tests, see the Section 3. Before conducting the test, the proband undertook a pre-conditioning time of 15 min in a relaxation room with the possibility to drink. The preparation for the test took another 15 min (weighing, measurement of blood pressure, adjusting the sensors, donning the underwear and protective ensemble). The probands wore the appropriate protective ensemble and performed a simulated work load by walking on a belt ergometer in a climatic chamber under given climatic conditions. The tests with the SCBA were arranged in such a way that two cylinders could be used sequentially during the test without interrupting the test:  
* Parameters of the probands: (a) 6 men (age: 29-53 years, height: 170-187 cm, weight: 69-92 kg, BMI: 20.2-29.4 (2 normal, 4 Overweight Class I), fitness level based on VO\({}_{\text{2 max}}\) value: from very poor (4 men, the worst 27.8 mL min\({}^{-1}\).kg\({}^{-1}\) for a man of age 29 years) to good (2 men, the best 37.3 mL\(\cdot\)min\({}^{-1}\).kg\({}^{-1}\) for a man of age 55 years)); (b) women (age 28-49 years, height: 158-176 cm, weight 56-71 kg, BMI: 20.3 to 26.1 (5 normal, 1 Overweight Class I), fitness level based on VO\({}_{\text{2 max}}\) value: from poor (1 woman, 28.4 mL\(\cdot\)min\({}^{-1}\).kg\({}^{-1}\) for a woman of age 28 years) to good (5 women, the best 33.6 mL\(\cdot\)min\({}^{-1}\).kg\({}^{-1}\) for a woman of age 36 years)). * Conditions in the climatic chamber: (a) \(-10\)\({}^{\circ}\)C and 25-35% rel. humidity (\(RH\)), (b) 5 \({}^{\circ}\)C and 20-30% \(RH\), (c) 25 \({}^{\circ}\)C and 20-30% \(RH\), (d) 35 \({}^{\circ}\)C and 15-25% \(RH\); air flow always 0.2 m/s, walking on ergometer (4 km/h, inclination 10%) in mode of 5 min acclimatization in the climatic chamber + max. 4 cycles of 20 min walking + 10 min rest, i.e., 125 min in total. * Max time achieved--reasons for termination of the test: (a) reaching the end of the test with standard test time limit 125 min, or (b) reaching the heart rate limit (\(HR_{lim}\) = 220 \(-\) age), or (c) reaching the body core temperature/rectal temperature limit (\(T_{relim}\) = 38.5 \({}^{\circ}\)C), or (d) proband's own request (headache, unbearably hot, nausea, breathing problems, etc.). Physiological parameters were monitored using the following systems: Almemo 2590-4S (Ahlborn GmbH, Holzkirchen, Germany, accuracy \(\pm\)0.17 \({}^{\circ}\)C) and Viridia (Philips Medizinsysteme, Boeblingen, Germany) with rectal probe Philips 21075A (accuracy \(\pm\)0.1 \({}^{\circ}\)C within the range 25 \({}^{\circ}\)C to 45 \({}^{\circ}\)C) using wired data transmission. The maximum test time achieved was recorded for all tests, as well as the reasons for test termination. The measurement of VO\({}_{\text{2 max}}\) and the related estimation of the fitness level was conducted on the METAMAX 3B (CRTEX, Biophysik GmbH, Leipzig, Germany).