1.1. Research Background
The construction industry plays a critical role in the development of nations and societies. Over 350 million people work in frontline building construction around the world [
1]. Construction accounts for approximately 7% of the total labor force in the United States, but construction workers account for approximately 20% of all industrial fatalities. With 15.2 deaths per 100,000 construction workers, construction is the third most dangerous industry after mining and agriculture. [
2]. Construction is a dynamic process with complex and changing working conditions as well as the possibility of unforeseen circumstances at any time [
3,
4], necessitating a great deal of effort from frontline workers to ensure that safety incidents do not occur [
5]. It is also distinguished by a heavy workload, long continuous working hours, unhealthy working postures, an unsuitable temperature and humidity of the working environment, and easy fatigue [
6]. Furthermore, due to a lack of sleep or mood swings [
7,
8], construction workers may already be fatigued when they begin working [
9]. Typically, 20-40% of construction workers exceed recognized physiological thresholds for physical labor [
10]. As a result of being unable to concentrate for extended periods of time or frequently experiencing mental fatigue, workers are frequently unable to respond appropriately to potential safety hazards, which can lead to accidents [
11]. It has been discovered that adverse reactions such as increased mental fatigue and cognitive decline in construction workers can result in hazards [
12]. Recognizing and predicting the occurrence of construction hazards can be accomplished through methods such as the creation of scene graphs with interaction-level scene descriptions [
13]. As a result, we can effectively reduce the occurrence of hazards during construction by monitoring both the subjective situation of construction workers and objective identification and prediction of hazards in the construction environment.
However, our research on the impact of environmental personnel is still dominated by subjective evaluation, which is the main technical tool used to study the impact of indoor environmental quality on occupants’ indoor comfort [
14]. Typically, people assess indoor comfort by completing various evaluation questionnaires, such as thermal comfort [
15], visual comfort [
16], acoustic comfort [
17,
18,
19], and perception of indoor air quality [
20,
21]. The same is true for outdoor building construction environments [
22], where we obtain current physiological conditions of construction workers primarily through subjective questionnaires [
12], and construction hazard identification primarily through personal inspections by the project manager [
23,
24], which are overly subjective [
25] and closely related to the project manager’s personal work status. Subjective evaluation allows us to obtain a large amount of data for research in a short period of time more conveniently, but it also has drawbacks, such as limited topics that can be designed; a wide range of investigations but insufficient depth; variable quality of survey results; and susceptibility to the subjective thoughts of the subjects [
9]. As a result, there is an urgent need for effective probes that can monitor the real-time status of building construction personnel in complex building construction environments. EEG, as a noninvasive and noninvasive neuroimaging technique, can provide accurate measurements of brain activity directly [
27]. The brain can plan and execute autonomous movements, and many purposeful actions and behaviors are accomplished through various computational sequences within the brain [
28], and EEG signals can also directly respond to nervous system activity [
29]. Currently, physiological monitoring, such as EEG, is widely used in indoor environmental research [
30,
31]. Hu et al. [
30] investigated the effects of various indoor lighting conditions on work efficiency by monitoring subjects’ EEG signals. EEG has a variety of applications in the field of sleep monitoring. PSG (polysomnography), for example, is used to determine sleep staging [
32,
33] and the presence of sleep-related disorders (e.g., OSA (Obstructive Sleep Apnea) [
34,
35], CSA (Central Sleep Apnea) [
36], RBD (Rapid Eye Movement Sleep Behavioral Disorder) [
37], and so on) in personnel [
38].
With the extensive development of cognitive neuroscience technology in recent years, EEG technology can now be used not only for rational monitoring of indoor people, but also for outdoor environments, such as monitoring outdoor people’s movement [
39,
40], observing pedestrians’ avoidance behaviors in dangerous situations [
41], and exploring outdoor thermal comfort and optimal outdoor environment [
42]. People who work outside for long periods of time are exposed to more complex scenarios that consume more energy than those who work indoors, making them more susceptible to physical and psychological fatigue, as is the case in the construction industry. The physical and mental health of construction workers is a source of concern due to their long hours of outdoor work [
6]. Many studies have been conducted in recent years on the application of EEG technology to the identification of hazardous behaviors and the monitoring of workers’ adverse reactions on construction sites, and the application of EEG in the field of construction is conducive to the in-depth understanding of the physical and mental state of construction workers during construction tasks, as well as the prediction and identification of hazards on construction sites, in order to elucidate In this paper, we first provide an overview of EEG technology, then summarize recent applications and research on the monitoring of workers’ adverse reactions and the identification of construction hazards in the field of construction, and finally look forward to the future development of this field.
1.2. EEG Technology
1.2.1. Four Functional Areas of the Brain
The human brain is the most complex structure known to man, with trillions of organized cells. The human brain is divided into two hemispheres, left and right, each of which controls the response body and receives information from it. Each hemisphere’s cerebral cortex is divided into four distinct lobes - frontal, parietal, temporal, and occipital - that are separated by deep sulcal fissures and have distinct functions. We’ve described the function and location of each lobe in
Figure 1. Understanding these will aid us later in understanding of the EEG technique.
1.2.2. Five Brain Wave Frequencies
Hans Berger discovered EEG activity in 1929 and invented a technique for measuring EEG with the goal of providing “a window to the brain.” There are five main brain waves in the human brain, as shown in
Table 1, ranging in frequency from low to high. These waves are closely related to states such as sleep, thought, cognition, arousal, and increased coordination when the brain is processing tasks. A typical EEG is made up of different frequency bands, and depending on the state of consciousness in which it is located, a specific brain wave will dominate, implying that different frequencies of brain waves correspond to different brain activities [
43]. Different EEG frequency bands correspond to different subjective feelings and tasks, and the energy or work Power Spectral Density (PSD) of the EEG waves in each frequency band can indicate that different parts of the brain are activated, reflecting different physiological states [
44].
1.2.3. The International 10-20 Electrode Placement System
The International 10-20 System electrode placement method, as shown in
Figure 2, is a standard electrode placement method prescribed by the AASM (American Academy of Sleep Medicine) that is designed to maintain a standardized EEG testing methodology to ensure that the results of a subject’s study can be compiled, replicated, and validly analyzed and compared using the scientific method.
Electrode placement is primarily cranial in reference and does not differ based on individual differences in head circumference or head shape. The sagittal line is the anterior-posterior line from the root of the nose to the external occipital ridge, and the coronal line is the left-right line between the anterior recesses of the ears. The focal point of the two lines is at the top of the head, where the Cz electrode is located. The sagittal lines were Fpz, Fz, Cz, Pz, and Oz from anterior to posterior, and the spacing between the points was 20% of the sagittal line length except for the distances between Fpz and the root of the nose and Oz and the extra-occipital ramus, which were 10% of the sagittal line length; and along the coronal line, from 10% of the left anterior recess of the left ear, T3, C3 and Cz. The other points’ locations are shown above. Arabic numerals were used to represent the electrodes, with the left hemisphere being odd and the right hemisphere being even, A1 and A2 representing the right and left earlobes, respectively, and the numbers decreasing from the lateral to the midline.
1.2.4. Portable EEG Monitoring Devices
Portable monitoring devices, such as smartwatches, have grown in popularity in recent years and can be directly connected to a person’s cell phone, making it simple for the user to view various data and understand his or her current physiological state (e.g., heart rate, blood pressure, skin temperature, sleep quality, etc.), in order to better understand his or her health.
The following portable monitoring devices are commonly used, as illustrated in
Figure 3: electroencephalogram, eye movement meter, accelerometer, skin temperature sensor, heart rate monitor, inertial measurement unit, and so on. People’s physiological signals can be monitored by various portable devices. Electroencephalograms (EEGs) can be used to monitor EEG signals, which are critical for judging construction unsafe behaviors and workers’ adverse reactions; construction workers can also wear portable eye-tracking devices to determine risks during the work process [
46]; and skin temperature sensors can monitor the skin temperature of construction workers at the moment to obtain the thermal sensation situation at the moment. Millions of people in various industries, including construction workers, use personal portable devices on a daily basis to monitor their heart rate and other health-related physiological parameters to ensure their well-being [
48]. Nnaji et al. [
49] demonstrate, using data from the National Institute for Occupational Safety and Health (NIOSH) fatality data, that the likelihood of accidents can be greatly reduced by the prudent use of intelligent portable monitoring devices.
The use of intelligent portable monitoring devices has the potential to improve construction safety and efficiency. Because the healthcare industry has been at the forefront of implementing this type of technology, there are now an increasing number of cases of it being combined with the construction field [
49]. Portable EEG monitoring devices that can monitor construction workers’ physiological states in real time without causing discomfort to their physiology are a novel idea in current research. Through application examples, this section introduces the Portable EEG monitoring device from two perspectives: Traditional Scalp EEG and Ear-EEG.
Traditional Scalp EEG
Wang et al. [
50] created a Scalp EEG with a set of electrodes and a microprocessor installed in a standard helmet to collect EEG data from eight different parts of the wearer’s brain. The mental fatigue of construction workers was objectively monitored using electroencephalography (EEG) signals, and the EEG signals of 16 construction workers were recorded while performing their tasks, and the time-frequency-energy data of the acquired EEG signals were processed using WPT (Wavelet Packet Transform) and CNN (Convolutional Neural Networks) to recognize their current mental fatigue state. The framework provides a cognitive fatigue state classification that matches the self-reported fatigue state with an accuracy of 88.85%, which can be useful in reducing construction risky behaviors and providing assistance in fatigue management for workers.
Chen et al. [
51] proposed and tested an EEG-based method for quantifying the mental load of construction workers. PSD (Power Spectral Density) was used to calculate the subjects’ post-experimental mental load. The results were consistent with the NASA-TLX (NASA Task Load Index) mental load score. A portable EEG helmet based on the Neurosky Think Gear module (NeuroSky, San Jose, California) was also developed to collect four sensing channels at different sensor locations, Fp1, Fp2, Tp9, and Tp10. The location of Fp1 was associated with logical attention; the location of Fp2 was associated with emotional attention. The two frontal EEG channels are compared to Tp9 and Tp10, which can be used as cross-channel references. In addition, an accelerometer was installed on the microcontroller to capture the three-axis motion of the helmet, as shown in Figure. In this experiment, each subject was asked to (1) sit in a chair and relax for 5 seconds; (2) climb a ladder (1 m high, requiring 3-4 s to reach the top); (3) select the appropriate bolt (2-3 s); (4) install the bolt (4-5 min); and (5) climb down the ladder and then rest. The installation task required each subject to select the appropriate nut and then tighten the bolt with a wrench. This task had to be completed three times by each subject. At the end of the experiment, all subjects were asked to complete a questionnaire to assess task load. Subjects wore helmets fitted with instruments and wirelessly connected to a laptop via Bluetooth during the experiment.
Figure 4 depicts a schematic diagram of the experimental subjects and equipment.
Figure 4a depicts the subjects with the experimental equipment,
Figure 4b depicts the EEG monitoring chip,
Figure 4c depicts the nuts and bolts used in the mounting activity, and
Figure 4d depicts the ladder that the subjects had to climb.
Aryal et al. [
52] created a sensing system that used infrared sensors attached to a helmet to monitor skin temperature at four different locations on the face, as well as heart rate and EEG signals. Physiological data from 12 construction workers were collected, and analysis revealed that the combination of skin temperature, heart rate, and EEG signals predicted worker fatigue with an accuracy of up to 82%.Li et al. [
53] created a quantitative method for assessing the level of mental fatigue in subjects based on traditional scalp-based EEG measurements by examining and analyzing EEG spectra, such as gravity frequency. By collecting EEG signals from relevant brain regions of the subjects using traditional scalp-type EEG, Xing et al. [
54] determined the positive effects of Progressive muscle relaxation and Trigeminal nerve stimulation sessions on the adverse emotions of construction workers at high altitude.
Ear-EEG
The traditional scalp EEG example was discussed above. Workers are bound to feel uncomfortable when wearing the helmet for an extended period of time due to the extremely limited space inside the helmet and the need to place the electrodes inside the helmet. Furthermore, workers will secrete a lot of sweat when working continuously outdoors, which will affect the electrode impedance and lead to inaccurate monitoring, making continuous EEG monitoring of workers inconvenient. As a result, we summarize another emerging and more popular EEG monitoring device, ear-EEG [
55,
56].
As shown in
Figure 5, Looney et al. [
57] developed the world’s first Ear-EEG in 2012, which drew widespread attention at the time. In general, the benefits of using Ear-EEG for monitoring include the fact that it does not obstruct the field of view and that the Ear-EEG is usually fixed in the ear canal for measurement, making it securely positioned and less likely to fall off. It is also less likely to sweat, avoiding the effects on electrode impedance caused by excessive sweating. While scalp EEG may require the assistance of experienced assistants, the Ear-EEG device can be simply placed in the subject’s ear, saving labor and improving the stability of continuous monitoring and monitoring efficiency.
Ear-EEG can be used to monitor facial expressions and body movements, and this research can aid in emotional recognition and determining the physical and mental states of construction workers. Matthies et al. [
55] created an in-ear headset based on Neurosky EEG sensors that can control various cell phone functions using human blinking motions and ear wiggling. In a later study, Matthies et al. [
58] used multiple electrodes on a foam earbud to detect 25 facial expressions and gestures using four different sensing techniques. The results showed that five gestures had an accuracy of more than 90% and 14 gestures had an accuracy of more than 50%. Athavipach et al. [
56] designed and used an Ear-EEG to achieve basic emotion categorization and demonstrated a high level of accuracy. The studies above have shown that Ear-EEG has a good performance in monitoring and acquiring EEG signals, which, combined with its headphone-like convenience, confirms that it can be widely used in fields such as medical monitoring [
59,
60] and sleep monitoring [
61].