The Influence of Deflection during a Fall
In the fall protection industry, the process of deflection is characterized by any piece of equipment that is displaced or misshapen under the load of arresting a fall or supporting a worker’s bodyweight after a fall has been arrested. Deflection most commonly occurs with a rope or wire cable style lifeline because they are flexible materials by nature and they are installed by being placed under tension. Deflection does not typically occur with rigid fall protection systems like I-beams and enclosed track.
One of the biggest dangers of a deflecting horizontal lifeline is that the anchorage connection point is moving in addition to the movement associated with the fall. Any motion associated with falling will need to be stopped in some manner. And the more movement that occurs during a fall event, the more force will need to be applied to the body as movement is being arrested. When a fall is arrested on a lifeline that can deflect, more force will be placed on a person’s body during fall arrest.
Another issue with deflection is the distance that a person can travel. The ANSI Z359 standard for the maximum distance a self-retracting lanyard can elongate during fall arrest is 54 inches. Although not every SRL is compliant with ANSI Z359.14-2012 standards, for the purposes of this blog, we are going to assume that 54 inches is the maximum distance that a person is expected to travel during the process of fall arrest when using an SRL. If the horizontal lifeline that is being used for fall arrest is flexible enough to become displaced under force, that displacement will add an additional travel distance beyond 54 inches to the worker’s fall. If a safety manager is only anticipating a specific travel distance during fall arrest (and they are not accounting for a deflecting lifeline) there could be additional (and unanticipated) travel during a fall event.
A fall distance due to deflection will not be the same for everyone because there are many variables that factor into deflection distances (like the weight of the attached worker, the type of lifeline, how it’s installed, etc.). In addition to requiring more force to stop a longer fall distance, the increased distance can also place a worker in danger of falling or swinging into dangerous obstacles. It is possible that a worker could experience an injury if they were to make contact with an obstacle during a fall event.
Fall protection system deflection can also cause a pull on the overhead lifeline which could potentially cause other workers who are attached to also fall and travel to the center of the lifeline. This occurs when one worker falls on a flexible lifeline and their body weight shifts to the center of the overall lifeline. If a flexible lifeline is suddenly placed under force, it is possible that the sudden force of the fall on the lifeline will cause any other attached workers to also fall. As a result of these movements on the lifeline, it is possible that the fall could influence multiple workers. And then, instead of only one worker falling, there could be several workers who fall as a result of the deflected lifeline.
Since there are so many dangers associated with deflection on rope or cable lifelines, it is best practice to take deflection into consideration when selecting and placing a fall protection system. Since a rigid horizontal lifeline can provide fall protection for people working at height without deflection, a rigid horizontal system can be a better alternative in certain applications. Because there are many potential outcomes that can occur after deflection, it is important to avoid deflection whenever possible.
Until the next time, stay safe up there!
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