AS NZS 1891.4:2009 Industrial fall-arrest systems and devices
3.2.3 Avoiding lateral swing—The pendulum effect
If there is a lateral offset between the line from the anchorage point to the operator and the line or direction of potential fall, in the event of a fall the operator may suffer hazardous lateral swing. This is commonly known as the pendulum effect. Two common consequences of the pendulum effect are illustrated in Figures 3.1(a) and 3.1(b). The hazard in the first case is a horizontal collision with a fixed object. In the second case it is a greatly extended fall distance. If the length of unsupported line is equal to or more than the height of the edge above the ground, the operator will strike the ground or other obstacle.
Where the pendulum effect cannot be avoided altogether by use of alternative or changeable anchorage points it shall be controlled to the extent necessary to minimize injury in the event of a fall. The following are ways in which this may be done:
(a) Dual anchorages The operator is connected to two separate anchorage points using a twin-tail lanyard in a way that will limit lateral swing in the event of a fall, as illustrated in Figure 3.1(c). Connection to the operators harness via a single energy absorber is essential to ensure that in the event of a fall the fall-arrest force does not exceed 6 kN.
(b) Diversion anchorage The lanyard assembly or anchorage line is diverted through a second anchorage point or a connector tethered to a second anchorage point as illustrated in Figure 3.1(d), and the lanyard or line runs freely through the anchorage point or connector. Care is needed in this case in determining what the maximum resultant fall-arrest force on the diversion anchor is likely to be. As demonstrated in Figure 3.1(e), it may be significantly greater than that on the primary anchorage. The calculated resultant force on the diversion anchor should be based on 6 kN maximum lanyard/anchorage line force and subjected to a factor of safety of 2.
(c) Edge stops Stops such as vertical projections are placed along the edge of the roof, platform or stage on which the operator is working, as shown in Figure 3.1(f). In the event of a fall, the distance the line can slide along the edge is limited by the stops. Edge stops should not be located in such a manner as to provide a trip hazard themselves, particularly if close to the edge of a roof or other potential fall location.