1. Introduction
The Social Security Administration (BPJS) Employment recorded the number of work accidents in Indonesia as 234,270 cases in 2021, as presented in
Figure 1. The data show an increase of 5.65% from the previous year, which had 221,740 cases. If we look at the trend, the number of workplace accident cases in Indonesia has continued to grow over the past five years. In 2017, the number of work accidents recorded was 123,040 cases. This number increased by 40.94% to 173,415 cases in 2018. The following year, work accidents rose again by 5.43% to 182,835 cases. Workplace accidents in the country increased by 21.28% to 221,740 cases in 2020. The number also increased again last year. According to BPJS, most of those accidents occurred in the workplace. They most often occur in the morning from 6:00 a.m. to 12:00 p.m.
Projects constructing bridges and elevated structures (elevated toll roads) carry a high risk of work accidents during the construction period. From 2017 to 2020, there were several work accidents on bridge constructions, flyovers, and elevated structures in Indonesia. Those work accidents caused significant losses to the projects, both in terms of material losses and non-material losses in the form of lives that cannot be measured in monetary terms. Construction projects, including bridge projects, consist of many tasks, and thus have a high potential risk of work accidents. The ILO (International Labor Organization) classifies the causes of workplace accidents into technical equipment factors, work environment factors, and human factors. The construction of a toll road necessitates a comprehensive plan to address safety and security issues during girder lifting operations [
1]. Technical equipment factors are causes of accidents due to the use of equipment that does not meet standards or is unfit for use [
2,
3,
4]. Environmental factors that cause accidents stem from the physical environment and the socio-psychological environment [
2,
3,
5,
6,
7]. Humans are the highest contributing factor to workplace accidents [
2,
3,
8], as workers do not know safe procedures (when performing hazardous activities) and do not comply with work requirements.
Construction projects have limitations in conducting work accident risk assessments, as the limited number of employees in a construction project results in insufficient data being used. Njogu et al. [
9] found that a lack of worker participation stopped the enforcement of occupational safety and health rules in Kenyan healthcare institutions. According to the research, the execution of safety protocols is enhanced when employees must follow directives [
9]. Bello et al. [
10] studied two research institutes in Nigeria and found that employees had not been given the attention they deserve to impact the program’s workplace health and safety [
10]. This means staff are not engaged in safety activities [
9,
10].
The background explanation above outlines the weaknesses in the assessment of bridge construction accident risks due to data assessment limitations; therefore, in this study, the use of Monte Carlo simulation is proposed. The application of Monte Carlo simulation is expected to address the data limitations in the assessment of bridge construction safety risks.
4. Result and Discussion
In this study, 24 associated risks were identified for the concrete bridge construction risks, including human factors, equipment, and materials. Respondents for this research came from contractor employees and focus on one of the bridge construction projects. Nine employees participated as respondents, all of whom were male and ranged in age from 28 to 57 years (
Table 1). The respondents’ education levels consisted of two degrees: bachelor and master. They had work experience of 8 to 22 years, but the most common experience spans were 11–13 and 20–22 years. Respondents were selected from employees with position knowledge of bridge construction safety aspects, such as project management, project engineering, quality control, HSE, and supervising.
Likelihood and severity evaluations make up risk assessment. The probability of an accident occurring is referred to as likelihood, and the magnitude of the impact of the accident is referred to as severity. A risk index was obtained by using the likelihood and severity numbers. This study used a probability and severity assessment scale with explanations for each criterion as shown in
Table 2 and
Table 3. The probability scale is presented in
Table 2, where almost certain is the smallest scale, or rare, valued at 1, and the largest scale, or almost certain, is valued at 5. The scale of severity is rated from 1 to 5 and details catastrophic, significant, moderate, minor, and insignificant severity, with the highest value scale impact of an accident, or catastrophic, being rated at 5 and the smallest value scale, or insignificant, being rated at 1.
Table 3 presents the severity scale (minor injury, can immediately continue working after receiving assistance).
Risk levels are categorized into four classifications: they denote very high, with a risk index value of 20 to 25, in red; high, with a risk index value of 10 to 19, in orange; medium, with a risk index value of 5 to 9, in yellow; and low, with a risk index value of 1 to 4, in green. The degree of the threat posed by prospective hazards is assessed using risk levels. Risks that are categorized as extremely high and high need to be subjected to meticulous planning to reduce their likelihood and provide mitigation strategies should they occur.
The risk assessment for bridge building is detailed in
Table 4, encompassing 24 risks analyzed for their likelihood and severity. The sample size consisted of contractor employees engaged in a bridge construction project, resulting in a limited number of respondents; hence, a Monte Carlo simulation was performed. The risk assessment results were analyzed for their mean and standard deviation, which would be utilized in the subsequent stage, the Monte Carlo simulation.
This research applies the Monte Carlo simulation to address data limitations in a bridge construction project. The frequency and the amount of data are compared to calculate the probability of each assessment scale, and this probability is then classified into five classes according to the scale used. Monte Carlo simulation utilizes probabilistic data derived from safety risk assessment results. The probability is derived from the frequency ratio of each assessment scale relative to the total data, with the probability of each risk assessed to obtain the overall probability value for the risks under evaluation.
Table 5 presents the probability analysis results for each risk in terms of likelihood and severity.
The probability data then calculate the cumulative value based on the risk class classification and then continue to analyze the interval of the cumulative risk probability according to the class, so that there are five classifications used that have risk probability intervals. We generated random numbers to select the appropriate interval for the created class, thereby obtaining the probability and severity values of the risk.
Table 6 presents an analysis of class creation for risk probabilities used in the Monte Carlo simulation.
In the Monte Carlo simulation process, random numbers are generated 10,000 times, and these random numbers will be evaluated to obtain the probability and severity values of the risks. The analysis of the risk index calculation for each risk is presented in
Figure 3. The risk index value is obtained by analyzing these probability and severity values. The analysis has shown that there are two risks with a high-risk rating on the index, such as a worker falling, which has a risk index of 12.5961, and a girder collapsing during installation, which has a risk index of 16.1873. Risks in the moderate category consist of a worker being trapped, workers being injured after being caught by steel reinforcements, concrete reinforcement failing, concrete formwork collapsing, a girder breaking, a girder rolling over, and a pile overturning.
The comparison between the direct assessment results and the Monte Carlo simulation analysis shows accurate results, with an average difference of 0.14%. The smallest difference is 0.02%, found in the risk of the concrete formwork collapsing, and the largest difference is 0.47%, found in the risks of a worker being punctured with a sharp object and a worker being injured by equipment. The analysis of deviation calculations for each risk is presented in
Table 7.
The Monte Carlo simulation applied in this study can be implemented well due to the limited data that can be obtained in bridge construction projects. Njogu et al. [
9], Bello et al. [
10] and Signoret, J. P et al. [
26] found the same due to the limited number of employees who understand construction safety. The number of simulations used, totaling 10,000 in this study, can produce comprehensive calculations similar to those in the investment feasibility study [
38]. A more comprehensive risk and potential return understanding was gained using this approach versus traditional methods.
This research uses random numbers 10,000 times to simulate the probability and severity to obtain accurate results, as performed by [
38,
39]. The number of iterations performed in Monte Carlo simulations is what makes them accurate. In general, the larger the number of simulations is, the more precise the result, but of course the computational time required is also extended [
39]. This tradeoff between accuracy and efficiency is a central challenge in Monte Carlo methods. The Monte Carlo simulation results in this study have high accuracy, where the highest accuracy is only a difference of 0.02%. Accuracy in Monte Carlo simulations carried out by several researchers also produced the same thing; a Hamiltonian Monte Carlo sampling method has shown comparable accuracy to state-of-the-art software products [
40]. Likewise, in a study of power indices, Monte Carlo simulations were run on 10,000 coalitions, with absolute errors of less than 10
(−3) [
38].
This study also includes the risk of a worker falling, with a risk index of 12.5961, which is in the high-risk category, and is a special concern for contractors to plan work safety so that this risk can be avoided. Workers falling from heights is a high risk which must be given careful consideration [
41]. Falls are a major occupational hazard, with important social and economic consequences for both workers and employers [
42]. According to Arachchige et al. [
43], in 2017 there were 227,760 workers that had fall-related injuries, with 887 workers dying due to fatal falls. These incidents not only harm employees’ health and quality of life, they also reduce workplace productivity and raise economic costs through health costs and worker compensation [
43].
A high risk of girder collapse during installation is also a risk, and in Indonesia in 2017 and 2018, several bridge projects experienced this accident. In the Indonesian construction industry, in large-scale infrastructure projects, the concern of girder collapse is very significant. Recently, several cases of girder collapse and other catastrophic events, such as cranes overturning, formwork collapsing, and material landslides [
44], have taken place. Girder collapse is a serious problem in construction accidents, but it is not the only risk factor. The Failure Mode Effect Analysis and Fault Tree Analysis methods have shown that the risk of a girder falling during mobilization is the dominant risk priority in girder bridge construction. Surprisingly, “daydreaming” was the most dominant cause of accidents in the construction field [
45], and girder collapse in Indonesia is part of a larger pattern of construction accidents where human casualties, asset destruction, and environmental damage can result. A comprehensive approach is needed to address this problem, which includes technical and human factors.
Monte Carlo simulation is very beneficial for conducting risk assessment and analysis on a construction project, where the number of employees performing the risk assessment is small, leading to less accurate results. This risk analysis can use commonly used spreadsheet programs with simple algorithms, allowing both small and large contractors to easily apply this analysis model. There are built-in functions and tools in Excel to generate random numbers, perform calculations, and run Monte Carlo simulations. A common process in this typically involves generating a model, specifying the input variables, with probability distributions, generating random samples, and analyzing the output [
46]. For example, the probabilistic nature of critical speeds and vibration amplitudes is clarified in rotor dynamic systems with the use of Excel in modeling uncertainties in bearing damping, clearance, and mass imbalance [
47]. A three-loop Monte Carlo simulation framework for seismic resilience assessment of Small Modular Reactors was developed and may be beyond the capabilities of Excel [
47]. In the same vein, more sophisticated tools are used for more complex structural analyses like stochastic buckling of porous functionally graded plates [
47].