Summary

Falls from heights are still a major cause of workplace accidents. Too often, workers don’t use lifelines because there is no anchor point available, or because they find that fixed anchor points limit their movements too much. This limitation can be overcome, however, with the use of a horizontal lifeline system (HLLS). This report is an update to and supersedes technical guide T-18, published in 1991. The update was necessitated by the obligation to equip lanyards with an energy absorber, added to the Safety Code for the Construction Industry (SCCI) in 2001. Furthermore, since HLLS anchoring systems are generally flexible, rather than rigid (a structural tower is an example of a rigid anchoring system), we felt it was important to take them into account in this update. This report is intended primarily for engineers who design HLLSs.

A brief review of existing analytical methods is given at the beginning. It concludes that the proposed methods are too complex or ignore the fact that the anchoring systems are flexible. The analytical method we propose here is simple enough to be easily calculated using an Excel spreadsheet, while taking into account the rigidity of anchoring systems. For the purposes of the study, the Excel version used included Visual Basic macros (Visual Basic for Applications, VBA). A method for designing multispan cables, missing from the 1991 guide, has also been added. Calculation nomograms similar to those presented in the earlier guide are suggested for 9.5 mm and 12.7 mm diameter cables. Last, there is a brief review of the method for calculating the required clearance.

The analytical method presented here has been validated in two ways: first, using dynamic fall tests and, second, with realistic simulations conducted using structural analysis software (SAP2000). The dynamic fall-testing campaign consisted of 42 tests that examined the influence of several parameters, including span, anchoring system flexibility, cable diameter and initial sag. As expected, we observed experimentally that the more rigid the anchoring system, the greater the tension in the cable. The experimental results were very comparable with those of the simple analytical method incorporated into the spreadsheet, which was actually rather conservative, in terms of both tension and sag; it may therefore safely be used to design HLLSs.

Static and dynamic digital simulations were done to replicate laboratory testing. The difference between nonlinear static digital simulations and those of the simple analytical model is very small. The simple analytical method using the Excel spreadsheet is therefore very effective and the switch to a static digital model has no significant advantage. The results from the analytical method were also compared with those of the digital model for testing not done in the lab: frozen energy absorber, multispan HLLS. The simple analytical model produced totally acceptable results for multispan cables. With regard to the dynamic digital model, it provides an accurate estimate of the tension and sag measured in the lab. The advantage of a dynamic analysis is therefore fairly limited, compared with a static analysis, given the small difference between the results obtained with the two types of analysis.

Last, the report shows that it is possible to program the analytical calculation method in an Excel spreadsheet and to incorporate various safety programs into it to prevent mistakes. The spreadsheet also has a flexible-anchoring-system validation function that corresponds to the design method required by the SCCI. The spreadsheet has been converted into a fairly user-friendly Web tool that enables users to determine cable sag and tension and the anchoring stanchion cross-section of an HLLS in about a minute, which is much faster than using sophisticated, expensive structural analysis software.