Risk analysis of chainsaw worker's motion and body posture using the REBA method in tree felling operations in forestry in western Guilan province

Background and Objective: Chainsaw-based felling is the predominant method of timber harvesting in the forest plantations of western Guilan Province. In these clear-cutting operations, operators are required to adopt various awkward body postures. Despite technological advancements and significant improvements in occupational health and safety (OHS) within the forestry sector, wood harvesting in this region remains heavily dependent on manual chainsaw operators. The repetitive and demanding physical postures assumed during these operations can lead to discomfort, increased risk of accidents, and long-term health issues. This study aimed to evaluate the body postures and repetitive movements of chainsaw operators during semi-mechanized felling of poplar (Populus spp.) trees, with the ultimate goal of improving operator comfort, safety, and occupational health.
Material and Methods: The study was conducted in the poplar plantations of District Two (Series 2), Gisum. A total of 430 body postures were recorded and analyzed across various work components, including moving between trees, undercutting, and back-cutting. Postural assessment was performed using the Rapid Entire Body Assessment (REBA) method. Operations were carried out using STIHL chainsaws. Data collection involved analyzing four hours of video recordings of the operators to identify different working postures. Scoring was then applied to various body regions, categorized into Group A (trunk, neck, and legs) and Group B (upper arm, lower arm, and wrist). Finally, based on the cumulative scores, five action levels were determined: Action Level 0 (low risk/unnecessary), 1 (negligible/may be necessary), 2 (medium/necessary), 3 (high/necessary as soon as possible), and 4 (very high/necessary immediately).
Results: The results indicated that the chainsaw operator's trunk was most frequently in a straight position during tree assessment (45.6%) and moving between trees (53.3%). In contrast, trunk flexion exceeding 60° was the most prevalent posture during undercutting (51.4%) and back-cutting (38.5%). Regarding neck positioning, the highest frequency during the tree assessment and undercutting phases was observed for extension or flexion exceeding 20° (54.4% and 51.9%, respectively). However, during back-cutting and moving between trees, neck extension/flexion of 0 to 20° was most common (46.7% and 53.3%, respectively). Analysis of leg postures showed that across all work phases, assessment, undercutting, back-cutting, and moving, the highest frequency corresponded to Code 1 (balanced weight distribution while walking or sitting). For upper arm positioning, Code 1 (20° forward or backward deviation) was the most frequent posture across the assessment, undercutting, back-cutting, and moving phases, with frequencies of 32.9%, 45.3%, 34.4%, and 46.7%, respectively. The forearm position most frequently recorded across all four work components was Code 1 (60–100° forward flexion). Similarly, wrist positioning across all stages predominantly fell under Code 2 (flexion or extension exceeding 15°). Overall, 0.7% of body postures were classified as Action Level 0, 13.71% as Action Level 1, 43.49% as Action Level 2, 34.89% as Action Level 3, and 7.20% reached Action Level 4.
Conclusion: The REBA analysis of felling components revealed that "tree assessment" and "moving between trees" fall under Action Level 2, indicating a need for further investigation and necessary ergonomic interventions to improve working conditions. Furthermore, the "undercutting" and "back-cutting" phases were classified as Action Level 4, necessitating immediate modifications to body postures during these tasks. The REBA index proved to be an effective tool for assessing musculoskeletal risks in forestry, particularly for felling operations. Integrating this method with other ergonomic assessment tools to evaluate various forestry operations could facilitate the acquisition of quality certifications for forestry companies.