Biomechanical evaluation & mitigation of occupational safety hazards related to manual rebar tying

Abstract

Construction industry around the globe is distressed with unsatisfactory occupational health and safety records. The situation is similar in Hong Kong where the issue has become of utmost importance. While the matter is of great concern generally for all of the construction trades, some of them need special attention such as rebar work. Rebar work has been under spotlight because of projected local shortage of rebar workers for several years to come, highly physically demanding nature of their work, and poor health and safety records. Published literature indicates that rebar workers are highly susceptible to work-related musculoskeletal disorders (MSDs) and fall accidents (FAs) as compared to other trade workers which could be partially attributed to prolonged rebar tying postures. Accordingly, this research endeavored to investigate the contribution of rebar tying postures to the development of MSDs and FAs among rebar workers. Advances in the health and safety informatics have provided us with the tools to identify and quantify risk factors arising from these rebar tying postures, and to evaluate appropriate mitigation schemes. To start with, owing to unknown prevalence of MSDs among construction workers, a systematic review and meta-analysis were conducted to comprehend the pervasiveness of musculoskeletal symptoms (MSS). The review highlighted that around one-half of the construction workforce face lower-back MSS every year and nearly one-third suffer from knee, shoulder and wrist MSS. The exorbitant prevalence rates necessitate further mechanistic studies to identify underlying associated risk factors of MSS and develop appropriate interventions. Secondly, to better understand widely prevalent MSDs among rebar workers, specially of lower-back, an experimental study was conducted to examine the biomechanical demands of typical rebar tying postures namely stooping, one-legged kneeling and squatting posture. These postures were chosen because of their wide adoption by the rebar workers. Surface electromyography was used to study muscle activations and motion sensors were used to study trunk kinematics. The results revealed that multiple risk factors are involved in each posture which could lead to development of MSDs among rebar workers. Thirdly, to encounter the highlighted risk factors, a low-cost ergonomic intervention of stool-sitting was evaluated using biomechanical, physiological and subjective measures. The intervention was found to be simple yet effective, highlighting the need and efficacy of task-specific prevention measures. Fourth, considering high rate of FAs in rebar workers, a study was conducted to investigate the temporal changes in standing balance after rebar tying in squatting, stooping and stool-sitting postures. To better understand the postural load during these postures, electromyography and oximeters were used. The study demonstrated that stool-sitting could significantly improve the standing balance owing to lesser postural load. Additionally, the results underscored the importance of individualized balance monitoring for proactive FAs prevention. Fifth, to enable individualized standing balance monitoring, a wearable inertial measurement unit (WIMU) and smartphone-based tool was devised to monitor static balance of the construction workers. The tool would enable proactive identification of fall prone workers and assist in informed decision making to prevent FAs. Overall this research work substantiates the use of health and safety informatics to improve the occupational well-being of the construction workers.