*2.3. Selecting Subjects*

Based on this study [35], researchers selected 12 participants. Considering the particularity of the miners, the volunteers were men. They were (22.5 ± 2.5) years old and weighed (56 ± 10) kg, which avoids, to a certain extent, the individual differences due to age, body type, etc. In addition, participants were healthy. Volunteers should have voluntarily participated in the study without compulsion. A total of 12 subjects were numbered sequentially. They were not allowed to take any medicine during the test to make sure not to overstimulate their nervous system. They kept an adequate sleep of no less than8h[36] before the 24 h of this experiment and wore comfortable clothes.

#### *2.4. Experimental Process*

The experiment was divided into two stages, before the experiment and while experimenting. Preparation before the experiment was as follows: (a) We contacted the subjects, explained what they need to pay attention to, and taught them how to use instruments. (b) We set the experimental environment, adjusted the laboratory temperature, humidity, and wind speed, and debugged tools.

During the experiment, except for researchers, volunteers, and recorders, other personnel were temporarily evacuated from the experimental site. The proper experimental steps were as follows: (a) 2 subjects wore the EDA wireless skin sensors and PPG/BVP wireless blood volume pulse sensors with the help of the researcher. (b) The volunteer adapted to a quiet test environment (50 dB) for 30 min before the test to ensure they were in perfect condition. (c) After 30 min, the researcher measured volunteers' physiological indicators in a quiet environment (50 dB) for about 3 min. At the same time, two subjects were asked to continuously watch the indicators displayed on the computer screen within three minutes. (d) The researcher changed the noise level to 60 dB and collected the subjects' physiological indicators when subjects were watching the computer screen (as a working condition). This step continued for 30 min. (e) After the first test, we removed the sensors, debugged them, and asked the 2 subjects of the second group to wear the sensors. We conducted the second group by repeating (a)–(d). We all together performed 6 tests and tested the

indicators of 12 subjects. (f) After all the 12 tests, we saved the test results. (g) We turned off the ErgoLAB human-machine environment platform, debugged all the instruments, and put everything in the experimental environment in its right place. (h) We conducted 60 dB/70 dB/80 dB/90 dB/100 dB tests at the same period (8.00–11:30 and 2:00–5:30) in the following 4 days. The experiment process was the same as (a)–(g).

It is very noteworthy that we performed the following things to make sure the results were credible: (a) The tests of the 5 experimental groups were carried out separately. That is to say, we tested indicators on only one noise level in 1 d to avoid noise adaptability. (b) We conducted a control group test before the tests of each experimental group. This minimized the possible errors caused by subjects' different conditions every day. (c) The test time was between 8:00–11:30 and 14:00–17:30 every day, and the experiment lasted for 5 days. (d) Each subject placed the wireless physiological sensors in the same place.
