1. Introduction
Despite thorough training and motivation, mistakes can still be made. In the workplace, the consequences of human failure have always been severe. According to statistics, more than 60% of deaths and accidents that occur globally each year are caused by human error [
1]. Accident and incident analyses have shown that human failure contributes to increased exposure to all accidents and health-hazardous substances. Human reliability analysis (HRA) has been investigated more effectively in recent years due to increased human failure events. Estimates of human error in road transport are 85%, 50–70% in nuclear power plants, 60–90% in the chemical industry, 70–80% in aviation, and 80–85% in freighters [
2]. Therefore, researchers have tackled human error to reveal the causes of these results.
Many studies have been undertaken to assess the role of human error in different industrial accidents. A series of studies have been undertaken to determine the initial possibility of a failure occurring. Current research involves the study of human error in the marine industry as the cause of marine accidents [
3]; maintenance operations in the marine industry [
4]; calculation of human error that will cause specific grounding events [
5]; the evaluation of human error in railway accidents [
6,
7]; human-induced actions with the potential to expose operators working in a radiation-emitting facility to radiation [
8,
9]; human error during the steam boiler operation [
10,
11]; and the human error probability in a probability security assessment of the reactor in nuclear power plants [
12]. Research has demonstrated that the human factor is an important risk factor in an industry, regardless of production and process.
Human reliability refers to the possibility that system operations will be undertaken by an individual accurately, within a certain timeframe, and without errors. A human reliability analysis (HRA) is used to predict human error in activities. A human reliability analysis (HRA) is one of the most powerful methods in risk assessments. Human error is the most significant factor affecting safety. The results of research have demonstrated that current reliability is not the same as expected reliability, and the root cause of this deficit is human error. The HRA is carried out as part of an analysis of system safety to estimate and analyze the possibility of human error in each sector. One of the most significant steps in the evaluation of human reliability is to define the factors that increase the likelihood of human error occurring and those that influence human performance [
13].
The first generation of human reliability analysis methods supposed that human behavior could be separated like a data computer. These models were largely adapted from expert analyses, such as the human error assessment and reduction technique (HEART) method. The second generation concentrated on human cognitive methods and modeling. Third-generation human reliability analysis methods, which are dynamic models, are grounded on cognitive simulation models [
1].
Electricity is the principal product of power plants and an essential component of contemporary life. According to the International Energy Agency, coal is the largest source of electricity production [
14]. The situation is similar in Turkey, where coal is important for the production of electricity [
15]. Despite all technological developments and processes, as in many industries, detrimental and devastating accidents still occur in coal-fired thermal power plants within the energy sector. Despite the popularity of coal compared to other power sources, very few studies have considered the different risks of coal-fired thermal power plants. Human behavior and manufacturing procedures play a significant role in crisis and accident management in thermal power plants, as well as in making human decisions.
Unexpected problems can occur in complex and high-tech equipment in a thermal power plant. Problems can often be caused by production error, material fatigue, human error, and other problems. In the event of a system failure, it is necessary to avoid human error. Despite the fact that accidents or incidents in coal-fired thermal power plants are often caused by human factors, there is not enough effort to increase safety and reduce the number of incidents in coal-fired thermal power plants.
Many researchers use multi-criteria decision making (MCDM) methods; to compensate for the shortcomings of one method, they combine two or more methods. Expressing risks based on personal views and value decisions, rather than numerical size, leads to uncertainty. In some cases, if there is no numeric data, there is a verbal language in risk assessment methods where terms can be given as vague expressions. Due to this feature of risk assessment methods, various studies [
8,
9,
16,
17,
18] have used the fuzzy AHP approach. Researchers and scientists have created a series of recent MCDM methods in the last decade [
19]. A new step weight assessment ratio analysis (SWARA) technique has been recommended by Kersulien [
20]. Although this is a new method, the choice of packaging design, architect selection, product design [
19], rational dispute resolution [
20], analysis of risks in coal supply chain management [
21], recruitment and staff selection [
22], and the power plant was used to solve many problems, such as location selection [
23].
This article provides more information on the relationship between accidents and risks in coal-fired thermal power plants, which are very dangerous and complex, by taking into consideration the literature. The study examined an incident that occurred in a coal-fired thermal power plant that was operating in Turkey. As this research was sectoral and based on specialist opinion and experience, this study used the human error assessment and reduction technique (HEART), a common approach often used to determine the human error probability (HEP). In addition, fuzzy analytical hierarchy process (fuzzy AHP) methods and step weight assessment ratio analysis (SWARA) from MCDM were used together. The purpose of using MCDM is the need for expert judgment. The weight of the error-producing conditions that constitute each risk was calculated with SWARA and fuzzy AHP, and the probability of human error was compared using the HEART method.
4. Results and Discussion
For the way of the boiler tube failure repair operation, human reliability assessment (HRA) can be calculated in accordance with the rule to find the HEP of operation tasks by the HEPs of sub-tasks given in
Table 9. In light of this information in
Table 9, the sub-tasks of a system of dependencies are designated in parallel or series. If failure of any sub-tasks makes the system completely inoperable, sub-tasks that form the system are identified as a serial system. For the system to operate, the achievement of either of the sub-tasks is adequate, and thus the sub-tasks are evaluated to be parallel. In the system, if serial sub-tasks have got a high dependence, the maximum HEP value is chosen. If the dependencies of serial sub-tasks have no or low dependencies, the values of HEP are summed. On the other hand, in the system, if the parallel sub-tasks have a high dependence, the minimum value of HEP is chosen. If the dependencies of parallel sub-tasks have no or low dependencies, the values of HEP are multiplied [
24,
30,
31,
32].
The overall HEP was calculated for each boiler tube failure repair operation for 7 essential tasks and 26 sub-tasks, with the aid of
Table 9. When analyzing step 1, four sub-steps should be performed appropriately to carry out step 1 successfully. Step 1 is considered a serial system when any of these four sub-steps fail. For this reason, the summed HEP value is found to be 7.11 × 10
−2 since four sub-steps have a low dependency. Similarly, step 2 will fail in the case any of the five sub-steps fail (high dependency, serial system). For this reason, the HEP value for step 2 is 1.56 × 10
−1. For step 3, the total HEP value is found to be 3.21 × 10
−1 (low dependency, serial system). For step 4, the total HEP value is obtained as 4.51 × 10
−3 (high dependency, parallel system), 1.99 × 10
−3 (high dependency, parallel system) for step 5, 1.56 × 10
−3 (high dependency, serial system) for step 6, and 1.37 × 10
−2 (high dependency, serial system) for step 7.
To calculate the failure (HEP) value of the boiler tube failure repair process, the 7 basic steps and the 26 sub-steps must be calculated precisely and successfully. If any of the steps are not successful, the operation does not take place properly. The final HEP value is 3.21 × 10−1 because there is a high dependency between them.
The relation between reliability (R) and failure (HEP) can be easily described with the formula R = 1 − HEP. Based on the precise calculation carried out, the reliability of the boiler tube failure repair was found to be 6.79 × 10−1. Therefore, recovery is performed to reduce the HEP value and improve performance reliability.
In accordance with the findings, the estimated failure (HEP) values of each sub-task for the boiler tube failure repair operation are in the range of 9.96 × 10
−5 to 2.70 × 10
−1. According to the results, sub-tasks that make a contribution to decreasing reliability are 2.1 (The load must be decreased by reducing the steam flow to the turbine and then the mill must be disabled in the boiler) and 3.4 (Check the Emergency Trip buttons and Fire Trip buttons). Remedial measures for sub-tasks 2.1 and 3.4 are proposed in
Table 10.
Table 10 presents actions to decrease human error rates with the highest human reliability (HEP) values for the boiler tube failure repair process among the overall sub-steps. Actions of control were generated with the co-decision of five specialists participating in the work since they have extensive experience and knowledge about thermal power plant operations. Thus, the safety level of the process is increased, and the probability of human error is decreased.
5. Conclusions
There is a limited amount of research that explores the relationship between the causes of human error and the negative consequences. The underwork on human reliability in operations in thermal power plants illustrates the importance of working. To enhance the level of operational safety in the thermal power plant, it is of major significance to increase the reliability of operations.
This article presented an HRA of boiler tube failure repair operation, one of the most serious processes in a thermal power plant, to enhance human reliability and safety because possible dangerous incidents generated as a consequence of weaknesses in safety experienced in the thermal power plant are fundamentally connected to human error. The boiler tube failure repair process, which is one of the most serious processes and operations that can cause damage to the system and accidents, was analyzed using a hybrid of the HEART with the fuzzy AHP and SWARA methods. The HEP values obtained by both methods were identical. Within this scope, the research findings are reasonable and consistent.
The HEART has deficiencies in the calculation of the APOE due to individual characteristics of experts that influence their decision. In this study, to work around these shortcomings and acquire an APOE value with high reliability and accuracy, the HEART was merged with the SWARA and fuzzy AHP to combine the decision of the expert group.
Operations should identify and implement appropriate control strategies and methods for each activity and risk. In this hybrid approach, linked to the knowledge and experience of the five experts in the coal-fired thermal power plant, experts can achieve the desired low-risk value by conducting regular reviews, verification by sampling, reporting, analyses, and supervision. Consequently, in order to decrease the human error probability, it is required to take appropriate actions depending on the task-specific error-producing condition (EPC).
Table 10 provides solution recommendations for sub-tasks 2.1 and 3.4. The conditions that generate errors in steps 2.1 and 3.4 were revised, and the human error probability was completely eliminated.
In the HEART method, it is difficult to obtain the assessed proportion effect value (APOE) because this value is obtained subjectively by the researcher or assessor. The APOE impact value in the study was evaluated with the opinion of more experts instead of a single expert. The common views of experts and the APOE values obtained through both the fuzzy AHP and SWARA methods were compared and obtained with close-to-one values. The contribution of the proposed methods in comparison to the conventional HEART method continues as follows:
In the expert-based fuzzy AHP–HEART hybrid method, experts used the linguistic terms independently and made the value of criteria more reliable and consistent.
In the SWARA–HEART hybrid method, five experts first sorted the criteria in order of importance and then weighted the criteria to analyze the risk. This method had changed risk values, unlike the conventional HEART method.
With the two recommended hybrid methods, hazards were analyzed precisely and accurately. In addition, this study highlighted the availability of the fuzzy AHP–HEART and SWARA–HEART hybrid methods to conduct human-focused risk assessments on coal-fired thermal power plants in Turkey.
In addition to this, the recommended method can also be practiced in several other serious processes in thermal power plants.
Consequently, the findings of this study can help develop the safety indicators and achieve the sustainable objectives of thermal power plants by offering practical solutions to control and eliminate errors.
The most remarkable limitation of the study is the use of just five types of expert experience and knowledge. Therefore, further research can be carried out using different multi-criteria decision-making methods and empirical studies with the opinion of more experts. The outcomes of the research will aid managers, experts, and safety researchers in achieving the lowest possible human error in the energy industry.