## 4 Discussion
### Characterization and Testing of the Sensors Integrated into the Smart Garment  
The developed gas sensor modules were tested statically using a test chamber (model EC01, manufactured by Figaro Inc., Arlington Heights, IL, Unites States). The sensor modules were put in the characterization chamber where clean air was present; then, a fixed gas concentration was established for 120 s, and finally, the gas was removed from the chamber. In particular, for each sensor, the corresponding STEL limit was used as the target concentration during these tests (Table 1). For O2, the sensor was first exposed to clean air with an oxygen level between 21% and 23%, and then the oxygen level was decreased to 16% for 120 s; afterwards, new clean air was introduced. Therefore, the output voltage transients were acquired using a bench multimeter (model GDM-8351, manufactured by Gwinstek, Taipei, Taiwan) for all used sensors, and thus, the corresponding gas concentrations were calculated using Equations (9)-(12) to verify different features of the used electrochemical gas sensors (sensitivity, response time, and recovery time) (Figure 21). Figure 21: Transient responses of the used electrochemical gas sensors: ME2-CO (**a**), ME2-CH2O (**b**), ME2-O2 (**c**), and ME3-H2S (**d**). Table 3 summarizes the parameters (response time, recovery time, and sensitivity) extracted from the above transient characteristics. The results are in good agreement with the data reported in the datasheets [35; 36; 37; 38], falling within the tolerance ranges provided by the manufacturer. In addition, five tests were carried out in an industrial scenario with the sensor modules installed inside the smart garment worn by a walking user. In particular, the measures provided by the wearable devices were compared with those provided by calibrated portable detectors. Specifically, the BW CLIP 4 multiparametric detector, manufactured by Honeywell Inc., was employed to measure the CO, H2S, and oxygen concentrations; on the contrary, the FP-3 IG detector, manufactured by GrayWolf Inc., was employed to detect the environmental concentration of CH2O. Table 4 summarizes the results of the above-described tests. As evident from the obtained results, the smart garment provides measurements in agreement with the reference values derived by the portable detectors, with a maximum deviation of \(\pm\)10% ascribable to the tolerance values of the components. In addition, a comparison between measurements provided by the smart jacket and those provided by reference instruments was carried out; in particular, for the HR, a professional arm blood pressure monitor (Medel Check model 3498, manufactured by Medel International SrI, Milano, Italy) was employed, whereas, for SpO2, a commercial pulse oximeter (model PR-10, manufactured by CocoBear, Shenzhen, Guangdong, China) was used. For body temperature (BT), an infrared thermometer (model HT-820d, produced by HT-Instruments Inc., Faenza, Italia) was used, and the air temperature (AT) was measured with a digital thermometer (model DM120-0-3, produced by Cooper Atkins Inc., Middlefield, CT, United States). Table 5 summarizes the data acquired by the smart jacket with the reference values, along with the corresponding deviations. As is evident, optimal agreement was obtained for all considered measurements, indicating the correct functioning of the sensors integrated into the garment. Finally, to highlight the contribution of the presented work, a comparative analysis with other similar scientific works is presented in Table 6 from the point of view of the detected number of biophysical and environmental parameters, availability of the harvesting section, and invasiveness.