Falls are the most common type of accident on construction sites in Japan. Preventing falls from roofs necessitates the installation of scaffolds around houses, but this regulation failed to ease the difficulty experienced by construction workers as they erected scaffolds in a disaster area during the Great East Japan Earthquake. The challenge stemmed primarily from debris around the site. The threat to scaffold safety was unacceptable given that the time spent on scaffold installation and dismantling was longer than that typically spent on roof work. When installing scaffolds around a house was problematic, the construction workers used lifelines and safety belts when working on roofs. Nevertheless, the advantages of this approach are limited by the absence of specific criteria that regulate the use of these safety devices. When a worker falls from a roof, the fixed end of a lifeline usually holds up the worker, thereby preventing crashes to the ground. The problem is that the standards for measuring or evaluating the appropriate amount of slack in lifelines are unclear. We therefore examined existing criteria by testing a full-scale roof device and using parameters such as lifeline slack in the experiment. The torso load during a prevented fall is absorbed by the adopted lanyard and lifeline. The lanyard’s hook hits roof eaves, thus increasing torso load. This result underscores the importance of providing a small lifeline slack.
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