Beyond OCRA: Predictive UL-WMSD risk assessment for safe assembly design

Abstract

In terms of occupational safety, one of the most important areas to consider is that of Upper-Limb Work-related MusculoSkeletal Disorders (UL-WMSDs), i.e. work-related disorders due to biomechanical overload of the upper limbs caused by protracted movements and/or repeated efforts throughout the workday. To estimate the risk associated with these disorders, the method known as the OCRA (OCcupational Repetitive Actions) Index is universally accepted; based on observation, it provides an index whose value is related to the expected percentage of pathological cases among the entire working population. This work introduces a different perspective to the problem in order to provide designers with a method – PRASAD: Predictive Risk Assessment for Safe Assembly Design – that makes them aware of the issues related to UL-WMSDs, starting from the earliest stages of the design of a new product and the related assembly workstation, well earlier than observing the activities associated to its production, that is when the assembly workstation is fully set and running. The main advantage of the method lies in the outcome, the PRASAD Index, which is fully comparable with the OCRA Index, so that the proposal leverages on the well-known OCRA standard approach. The new method, aimed at a use in the design phase (of a new workstation for a new product), is potentially useful for a conventional risk assessment of existing workstations as well: it combines the rapidity of a checklist for the initial screening with a level of detail that is characteristic of advanced methods, such as the OCRA Index. Finally, PRASAD represents an innovation in the risk assessment of UL-WMSDs because of its feature of modelling the concept of “Technical Actions”, which enables estimating (and taking into account) the repetitiveness of tasks, based on technical design and production management data.