Effect of work shift on ergonomic variables in wood harvesting machine workstations

Abstract

Brazilian forestry companies have increasingly adopted shift work to increase productivity, including night operations, often without fully understanding the associated ergonomic risks under real operating conditions. This study evaluated the effect of work shifts on key ergonomic variables at machine workstations in eucalyptus plantations in southern Brazil. Data were collected during cutting, extraction, and processing operations using a feller buncher, grapple skidder, and landing processor, in both day and night shifts. Whole-body vibration was assessed according to NHO 09, noise and thermal comfort were evaluated based on NR 15 and NR 17, and operator visibility was analyzed using the Skogforsk ergonomic guideline, with results compared to Brazilian regulatory limits. The results showed that ergonomic risks were more strongly influenced by machine type and operational conditions than by work shift alone. Differences between shifts were associated with changes in machine operation caused by visibility, travel speed, and terrain conditions, which affected vibration and noise exposure. The grappler skidder consistently presented the most critical situation, with vibration levels reaching 1.62 m/s² and noise levels up to 89 dB(A), exceeding recommended limits. In addition, greater lateral head movements indicated reduced visibility, particularly during night operations. These findings indicate that ergonomic risks in mechanized timber operations are primarily driven by operational demands rather than shift schedules, emphasizing the need for targeted interventions in equipment design, maintenance, and task organization to improve worker safety and performance.