Risk assessment of repetitive tasks: A comparative analysis among different methods to update the maximum frequency allowed

Abstract

A comparison in terms of the maximum frequency of movement allowed in the no-risk area, when varying the force and the duty cycle, was made among the follows methods: Strain Index (SI), Revised Strain Index (RSI), Occupational Repetitive Action (OCRA) Index and ACGIH (TLV). The RSI provides similar results to the OCRA Index and ACGIH(TLV) in less than 1/3 of the overall pre-set combinations of force (BS) and duty cycle (DC). Some of the highlights are as follows: the ACGIH (TLV) method allows 6 exertions per second in the net time of the cycle, while the RSI less than 1, in the hypothesis of BS=1 and DC=60%; in the same conditions, but for a DC=100%, the ACGIH(TLV) allows almost 2 exertions per second while the RSI and the OCRA Index do not consider any frequency of movement as “safe” in this circumstance; in the same conditions but when DC=20% and BS=5, the RSI method allows less than 0.5 exertions per second, while using the OCRA Index it is possible to stay in the “safe” area even if the exertions per second are over 4. More epidemiological data would be desirable to better define the boundary conditions used by the methods.