A cause and effect decision making model of factors influencing falling from height accidents in construction projects using Fuzzy-DEMATEL technique

All construction projects carry some levels of risk. The construction projects involve numerous uncertainties, multiple intricacies, varies techniques, and divergent environments. So that, workers in the construction industry are at greater risk because of the dynamic nature of the activities and momentous changes in working conditions in comparison with other industries. The construction projects involve many factors, interdependencies, and correlations, which makes determination of exact cause and effect very difficult. Therefore, these factors play a significant role in decision making and may affect performance of a project.
The construction process frequently requires workers to work at height. The risks associated with working at height are often increased by adding accessibility and mobility restrictions. Falling from height is one of the most important causes of workers' fatality in the construction industries and constitutes a paramount part of the safety plans in the construction projects. Identifying the effective factors and sub-factors in the occurrence of this accident will be helpful in setting priorities for preventing and providing solutions in reducing their severity. The purpose of this study was to investigate and identify the factors and sub-factors affecting falling from height accidents and to determine the cause and effect relationships among them in the construction projects, using the fuzzy-DEMATEL technique.

In order to carry out this descriptive-analytical study, information of the Occupational Health and Safety (OHS) department of five construction projects have been used. The statistical society of the present study was the workers of five construction projects of a gas refinery in the south of Iran, which 4000 people, on average, were involved in these projects from 2011 to 2015. After reviewing the scientific literature, project reports, and guidelines, factors and sub-factors affecting the occurrence of falling from height accidents in the construction projects were determined based on the experts opinions. Snowball method was used to identify experts and determine the statistical society. Fuzzy-DEMATEL technique, as one of the methods of decision making based on paired comparisons, was used to identify the cause and effect relationships among factors and sub-factors. Based on this technique, the pairwise comparison matrices of the factors and sub-factors were formed and sent to 10 health and safety experts. Next, the views of experts were aggregated via the mean fuzzy method, and then the cause and effect relationships were determined based on them. The step-by-step process of the research is as follows: 
Step 1: Identifying research factors and sub-factors
All of the reported events were investigated between 2011 and 2015 and 74 out of 377 occupational accidents were considered as falling from height accidents. Considering the information of OHS department and literature review of effective factors in the occurrence of construction accidents, 70 factors and sub-factors were identified as effective factors in falling from height accidents. According to the objectives of the study and status of the projects, the identified factors and sub-factors divided to 3 main factors (organizational, individual, and environmental factors) and 14 sub-factors (management commitment, safety culture, mutual understanding, supervision/inspection, and size organization/project as an organizational factors; education, training hours, personal protective equipment (PPE), age/experience, and psychological/occupational stresses as an individual factors; thermal stress, interference, level smoothness, work platform height as an environmental factors).
Step 2: Data analysis and use of DEMATEL technique
In this research, Fuzzy-DEMATEL technique was used to construct a sequence of extracted data. This technique is one of the decision making methods based on pair comparisons with the benefit of expert’s judgment. The concept of this approach is based on the assumption that a system consists of a set of criteria and the pairwise comparisons of relationships between these criteria can be modeled by mathematical equations. DEMATEL technique is an approach to identify the cause and effect relationships among multiple factors in order to properly understand the problem. In general, it is very difficult to determine the opinion of experts with precise numerical values, especially in terms of uncertainty since the results of the decision depend heavily on unclear and subjective arbitrary judgments. These uncertainty conditions have led to the introduction of a fuzzy logic in the metamaterial technique. Therefore, in the Fuzzy-DEMATEL technique, fuzzy language is used which facilitates decision making in uncertainty conditions [37]. All calculations were performed in Excel (version 2013). The steps to implement this technique have been presented step-by-step based on the study of Li et al.
I) Calculation the direct relation matrix:After gathering the experts' view, a fuzzy direct relationship matrix ( ) was formed and the fuzzy mean method was used to aggregate the views of experts. Assuming that n experts have expressed their idea about the relationship between the indices and each component of the fuzzy direct matrix is displayed by then by can be calculated from Eq. (1) as follows: 

II) Normalizing the direct relation matrix:To normalize the values of the direct contact matrix, of each row must be calculated. Then, the fuzzy normal matrix ( ) can be calculated from Eq. (2) by dividing each component of by the maximum attained :
III) Calculation of the total-relation matrix
To calculate the total-relation matrix, the fuzzy normalized matrix is divided to three definite matrices as follows:
Then, the identify matrix is formed and the following operations are performed:
Then, the fuzzy total-relation matrix is computed by using Eq. (4).

The results of this research showed that among the main factors, organizational and individual factors were known as causal factors, which indicates importance of these factors and their impact on other effective factors in falling from height accidents. On the other hand, among various sub-factors, the management commitment, safety culture, monitoring and inspection, organization/project size, education, and work platform height had the highest effects on the falling from height accidents and were considered as causal variables. In the present study, management commitment, as one of the organizational sub-factors, had the highest impact and was considered as a causal variable.
According to the findings of this study, it can be concluded that four organizational sub-factors of mutual understanding, management commitment, safety culture and organization/project size, one individual sub-factor of education, and work platform height as an environmental sub-factor had the significant impact and were among the causal variables, while the rest of sub-factors were the effect variables. Also, the monitoring/inspection sub-factor has the highest interaction with and impact on other sub-factors.

Falling from height is considered as one of the most important accidents, leading to death and physical injuries in construction projects. The findings of this study showed that a greater attention to organizational factors and their dimensions (as hidden and effective causes to prevent falling from height incidents) is necessary since an organization plays an important role in the design of work processes, design and implementation of safety management systems, commitment to safety and employee participation, and choosing the best people according to the requirements for the health and safety programs of the projects. The results of this study also showed that it is necessary to pay more attention to the management commitment and awareness of the workforce by training them in the construction projects. Hence, a greater attention to organizational factors and their sub-factors in the construction industry is essential for preventing falling from height incidents. Therefore, more attention to the organizational factor and its sub-factors in the construction industry is required to prevent falling from height accidents.
Keywords: Falling from height, Fuzzy-DEMATEL technique, Construction projects, Workers.