Abstract

This research seeks to formulate integrated risk mitigation strategies by identifying inherent risk factors specific to each construction phase of Modular Construction—the cornerstone of Off-Site Construction (OSC), which is increasingly adopted to enhance productivity and site safety. While modular construction yields positive outcomes, such as a reduction in overall accident frequency compared to traditional Reinforced Concrete (RC) methods due to shortened onsite work hours, it concurrently introduces unprecedented categories of major accident risks, particularly during the lifting of heavy modules and high-altitude assembly. To address these challenges, this study structuralizes the modular construction process into four distinct stages—Delivery, Lifting, Assembly, and Finishing—and identifies critical risk factors for each stage through a dual approach involving domestic and international case analyses alongside expert Failure Mode and Effects Analysis (FMEA). The findings indicate that the most critical risk factor in modular construction is the dynamic instability of modules during the lifting phase caused by center-of-gravity imbalances. Specifically, in cases of asymmetric modules where internal finishes and MEP (Mechanical, Electrical, and Plumbing) systems are concentrated on one side, a high probability of unexpected tilting was identified, which can lead to crane overturns or module falls. Furthermore, the assembly and jointing stages were found to be primary drivers of human casualties, such as falls and crushing accidents, due to frequent high-altitude tasks performed on module tops and within confined connection spaces. To fundamentally mitigate these risks, this study proposes a three-tier response framework based on the Hierarchy of Controls. First, as an Engineering Control, worker exposure to hazards must be inherently blocked by implementing BIM-based pre-lifting simulations and adopting smart equipment such as self-leveling spreader beams and auto-release hooks. Second, as an Administrative Control, the establishment of specialized and standardized lifting plans is required, incorporating Design for Safety (DfS) to integrate safety facilities from the design phase and the deployment of dedicated modular signalers. Third, as an Educational Control, workers' risk perception must be enhanced through cross-safety training between the fabrication factory and the site, as well as VR-based virtual safety experience programs for high-risk processes. This study suggests a paradigm shift in the safety management of modular construction sites—from a reactive approach to a proactive, prevention-oriented system centered on design and factory fabrication. The proposed mitigation strategies are expected to serve as foundational academic data for establishing practical occupational safety and health management guidelines for future modular projects.