Quantifying Biomechanical Demand During Manual Overboard Rescue: Scenario-Based Application of the Revised NIOSH Lifting Equation

BackgroundMaritime first responders frequently perform manual overboard lifting during rescue operations, placing them at high risk for musculoskeletal injury, particularly in the lumbar spine. Conventional ergonomic guidelines, including the Revised National Institute for Occupational Safety and Health (NIOSH) Lifting Equation (RNLE), were developed for controlled, symmetrical lifting and do not adequately capture the biomechanical and environmental demands of overboard recovery.PurposeThis study aimed to quantify biomechanical demand during overboard lifting from vessels with 1.8- to 3.0-m freeboard and to evaluate injury risk under conditions exceeding standard RNLE assumptions.MethodsThe RNLE was adapted to estimate Recommended Weight Limit (RWL) and Lifting Index (LI) for overboard lifting tasks. Scenario-based analyses examined object masses (0-140 kg), horizontal reaches (25-50 cm), and vertical lifting distances (0-175 cm). LI values were calculated at both lift origin and destination to capture phase-specific biomechanical risk.ResultsUnder idealized conditions, LI exceeded the recommended safety threshold (LI > 1) at loads as low as 15.6 kg for a horizontal reach of 25 cm. For a human-sized load of 90 kg, LI ranged from 3.9 to 7.8 depending on horizontal reach and vertical displacement, indicating substantial biomechanical overload. Increasing horizontal reach from 25 to 50 cm increased LI by 40 to 60% across all load conditions. LI exceeded 1 at both the lift origin and destination for all modeled loads ≥20 kg and vertical displacements ≥50 cm, highlighting the elevated risk inherent in these tasks.ConclusionManual overboard lifting imposes significant biomechanical strain that frequently exceeds conventional ergonomic limits. Task-specific metrics derived here provide quantitative guidance for injury prevention, including pre-employment functional screening, progressive task-specific conditioning, and the use of mechanical assistive devices. These findings support evidence-based occupational health strategies for maritime first responders and other personnel performing high-risk lifting tasks in dynamic environments.