Overcoming Physical Obstacles with Four-Wheeled Hand Carts: An Evidence-Based Ergonomics Guideline for the Commercial Roofing Trade

Hand carts are used in nearly every construction trade for material handling. Nonetheless, the use of carts can be strenuous and lead to musculoskeletal injuries. This is particularly the case when carts are used in hazardous working conditions, such as physical obstacles and ramps. Unfortunately, little is known so far about the effects of these physical environmental hazards on cart operations. This study aims at understanding the operating forces required to overcome physical obstacles with a type of four-wheel carts commonly used in the commercial roofing trade. We varied obstacle heights, load weights, space constraints, and tire types in the laboratory experiment to reveal how hazardous an obstacle will be under different working circumstances commonly seen on construction sites. The space constraint is identified to be the most significant factor that determines the operating forces required to surmount an obstacle. This finding suggests the necessity of optimizing workplace layout to refrain workers from overcoming obstacles in a constrained space where the travel distance from cart to obstacle is less than 61 cm. An obstacle begins to yield noticeable impeding effect when it is higher than 3.8 cm, and any obstacle less than this threshold is not very hazardous especially when no space constraint is present. In addition, we found that pneumatic (air-filled rubber) tires are more favorable over solid (polyurethane foam-filled rubber) tires in overcoming obstacles and thus can be a convenient solution if it is infeasible to eliminate obstacles. The research findings can be used as reference information to develop numerical standards for manual cart handling, such as safe load restrictions and operating techniques, to increase ergonomics awareness and prevent musculoskeletal injuries in construction.