Soft retention in height fall safety devices

Abstract

Height falls in construction work cause fatal or serious accidents every year. Safety devices used to avoid this are supposed to stop the falling worker by developing forces that are low enough to prevent serious injury being caused during the retention process. In this paper three safety systems are analysed: collective protection such as safety nets (V-type) or provisory edge protection (C-class guardrails) and personal fall arrest systems (with a harness). There are many biological and mechanical variables involved in the retention process. Maximum or minimum values are needed for kinetic energy to be absorbed; the forces against a retained worker or system deflection, respectively, are required by certain codes governing the safety systems. Other codes only establish limits for some of these variables. Code criteria about cited requirements are not homogeneous and sometimes they are even inadequate due to a lack of knowledge about the relationships and implications concerning the mechanical variables. The corresponding interaction is difficult to evaluate and requires expensive experimental studies to be carried out on instrumented real size samples. Nevertheless, in the last decade, research on safety systems has been done on refined finite element models that can perform dynamic simulations of the impact. This paper contains important conclusions drawn from the original contributions of authors that suggest making relevant improvements to some of the corresponding codes. Comparisons of cheaper numerical predictions and real size experiments have proved that finite element models can be reliably used to analyse and design these safety devices.