To a safety professional, it is shocking how often horizontal lifelines (HLLs) are offered as a means to abate fall hazards. In spite of the repeated warnings from OSHA, ANSI, and many safety professionals regarding the complexity of HLLs, employers often see them as an inexpensive method to solve a nagging fall protection problem.
However, it is a fact that HLLs are complex mechanical systems, and if they are not treated as such, the consequences can be fatal. This paper will address the complexity of HLLs and provide ideas for effectively using HLLs in the appropriate circumstances.
A simple Google search for "horizontal lifeline system" results in hundreds of HLL "systems" offered for sale. The term "system" in this case often refers to the components that make up the horizontal lifeline, such as the rope, connectors, in-line shock absorber, etc. The use of the word "system" is often misunderstood and confused with OSHA's and ANSI's "part of a complete fall arrest system." The HLLs offered for sale, or any HLL for that matter, are only one component of a complete fall arrest system, which also must include analysis of the supporting structure, training and procedures for using the equipment, as well as rescue methods. Already the complexity of HLLs becomes apparent.
To understand why HLLs are so prevalent, it's worth looking at what problems people are attempting to solve. HLLs are typically chosen when relatively long distances (more than 30 feet) must be covered with little or no overhead structure in between. At first glance, they seem to be a logical solution when motion in a linear horizontal direction is required, such as when working on a bridge crane runway or on top of a tractor-trailer. As shown in Exhibit 1, HLL systems that are supported from a lower beam using a stanchion are common on construction sites. These systems appear to offer a simple solution to the problem of having no overhead structure that can be used to support alternate fall protection methods.
Exhibit 1 - This drawing represents a typical construction site HLL (available in full paper).
However, many HLLs are installed without regard to the tremendously high forces the cable puts on the upright stanchion and supporting structure. As will be described later in this paper, cable tension in the range of 10,000 lbs. is not difficult to generate. Most structures are not designed to support these types of forces in addition to normal dead, wind and snow loads. Therefore, the need for additional reinforcing should be factored into the decision to use an HLL. One way to reduce the end anchorage load is to allow the cable to deflect more in the event of a fall. However, when compared to a rigid monorail type fall arrest system, HLLs already deflect significantly. Many times, they are used in situations where there is inadequate clearance to the ground or a lower obstruction.