We often receive questions about horizontal lifeline systems, the parts, the span distances, the deflection etc. That’s why, in this blog, we’d like to discuss the anatomy of a horizontal lifeline system, HLL in short.
A horizontal lifeline system is a cable track, permanently fixed to a structure by means of several individual anchor points. A user needs to connect to the system by wearing a full body harness, and using a lanyard and runner. Depending on the setup of a system the horizontal lifeline system can be used as a fall restraint or fall arrest system.
Components of a horizontal lifeline
A horizontal lifeline system is built up out of several components. The system consists of a flexible wire rope which is attached to at least two anchor points.
All lifeline systems have two end points. These are supports on the anchor points at the ends of the system, where the lifeline is fixed and tensioned. This particular lifeline system also has additional posts, the anchor points between the end points, an intermediate and a corner support.
All supports are fixed to posts that are anchored to the structure of a building. This type of XSPlatforms anchor point is installed on top of the roof structure with only one drilling hole. The base plate is sealed with a rubber O-ring, on which the top components are installed. The distance between each anchor point, or post, is called a span.
Fall clearance of a horizontal lifeline system
When a system user falls while attached, the system will deflect in the direction of the fall. The higher this deflection, the larger the fall clearance needs to be. The fall clearance is the distance that’s available for a person to fall without hitting a lower level, for example the ground.
The calculated fall clearance cannot be higher than the available distance between the working surface and a lower level. After all if the required clearance is higher a person could hit the ground before their fall is properly arrested.
This is one reason why the setup of a horizontal lifeline needs to be properly calculated.
Another thing to consider in system calculations are the forces exerted on a system in the case of a fall arrest. The span distance and sag angle, for example, influence the Maximum Arrest Load (MAL). A long span leads to a smaller sag angle, which causes a higher impact force on an end/corner anchorage when a fall is arrested. To protect a building’s structure integrated energy absorbers are necessary.
XSPlatforms often works with HLL systems with XSBending kits, these are patented posts that bend in the direction of a fall and increase the sag angle, thus decreasing the loads exerted on an anchor. Another form of integrated energy absorption is the XSDynamic, this extends the cable trajectory, catching most of the blow. A combination of both energy absorbers can also be made to accommodate more users.
But a fall does not only put strain on a structure, but also on the person whose fall is arrested. Therefore a Personal Energy Absorber (PEA) is necessary for any fall arrest system. This will protect the user, while the other absorption option protect the building.
All in all there are a lot of factors that need to be considered while calculating a horizontal lifeline. This is why XSPlatforms developed an online calculation tool, ODIN. ODIN indicates if the solution is safe to use and complies with selected standard, or if changes are required.
Download the anatomy of a horizontal lifeline infographic
We have made a schematic infographic of the anatomy of a horizontal lifeline that you can download and print.