Comparative analysis of three methods of risk assessment for repetitive movements of the upper limbs: OCRA index, ACGIH(TLV), and strain index

Abstract

PurposeLiterature proposes different methods for risk assessment due to repeated movements of upper limbs. The results are sometimes different even if methods are applied in the same work conditions. This study, based only on hand/wrist work involving ulnar deviation, compares three methods among those most used for distal upper extremity (DUE) work-related musculoskeletal disorders (WMSDs): OCRA Index (O.I.), Strain Index (S.I.) and ACGIH(TLV). Design/methodology/approachThe work analyzes the algorithms of the methods in terms of number of parameters considered in the formulas, range of variability for each one, and their interaction in determining the final results. Starting to calculate maximum frequency that each method allows in no-risk conditions (varying force and duty cycle), specific scenarios were also created varying one parameter at a time among those determining risk (i.e. force, posture, recovery time …) for a better comprehension of the different algorithms proposed and the provided final results. FindingsThe results are generally different: in the 21 scenarios analyzed, all the methods indicate the same level of risk in only 6 cases when using the formula for the calculation of the hand activity level (HAL) in ACGIH(TLV), and in only 3 cases when using the table. Force bears a higher relative weight for ACGIH(TLV) compared to the others methods: the number of exertions per second allowed in the no-risk zone decreases markedly as the applied force increases. The S.I. was noted to generally be the most precautionary among those examined regarding the frequencies of movements allowed in the no-risk range. The use of categorical multiplier instead of linear, made the results mainly different in the intermediate risk conditions. Originality/valueThe differences in results are due not only to the different number of parameters considered by methods but also to the different risk limit values inside each algorithm. A greater amount of epidemiological data would be desirable in order to better define the conditions to be considered harmful for a worker performing repeated movements of the upper limbs.