The Principle of Fall Arrest

People who are regularly involved in activities held at great heights face fall hazards. Risks of injury and death due to falling are higher for workers employed in the construction and maintenance of high-rise buildings and people whose hobbies involve climbing steep slopes, such as rappelling and mountain-climbing. These people should be equipped with fall arrest lifelines or should be located within an area with general fall arrest nets. There are two main forms of fall arrest: general fall arrest and personal fall arrest. General fall arrest involves the use of protective devices in a fall hazard area so that workers who accidentally fall do not experience severe injuries or, worse, death. Protective devices include nets that are stretched around the elevated structure through lateral steel tubes. For personal fall arrest, on the other hand, a person uses a set of ropes to keep his or her body stable at a certain point of elevation. Fall arrest is about absorbing energy. The impact of fall can be derived from the force of gravity and the distance of the fall. By studying the relationship between these elements is a fall situation, a fall arrest mechanism can be designed to absorb the energy formed at impact. For instance, two objects are dropped at the same height but on different surfaces. One object is dropped on a cemented surface, while the other is dropped on a puddle of mud. The weight of the objects is equivalent to the initial energy to be dissipated by the surfaces upon impact. There should be sufficient arrest distance to absorb the energy of impact and conduct the fall arrest. Arrest distance is proportional to the density of the surface and inversely proportional to the energy of impact. In other words, arrest distance is usually longer at a softer surface, which makes for effective fall arrest. The energy of impact is absorbed well by a soft surface, helping the fallen object preserve its form. The same principle is applied in the manufacture of a fall arrest lifeline. The lifeline’s ropes are made elastic, so that a sufficient energy of impact can be absorbed. The rope works like a spring that stores as much mechanical energy as possible and releases it to meet the same energy at equilibrium.