Falls from height are a leading cause of serious injuries and fatalities in construction and industrial settings. Protecting workers requires a comprehensive safety strategy, often involving specialized engineered solutions. Personal Fall Arrest Systems (PFAS) include two fundamentally different approaches: fall restraint and fall arrest. Understanding these distinctions is foundational to selecting and implementing the correct equipment for any job at height, as the choice determines the equipment used, safety calculations, and worker mobility.
Understanding Fall Restraint Systems
Fall restraint systems eliminate the fall hazard by physically preventing a worker from reaching an unprotected edge. This preventative approach limits the worker’s movement, ensuring they never pass over the point where a fall could occur.
The system relies on components that maintain a fixed distance between the worker and the fall hazard, such as a simple, non-shock-absorbing lanyard or a tether. The length of the connecting device is calculated to keep the worker away from the edge. The anchorage point must support a static load of at least 1,000 pounds per attached worker, a requirement much lower than for dynamic fall systems.
Because the forces involved are static, fall restraint does not require complex energy absorption mechanisms. The system is only expected to hold the worker’s weight against the tension of the tether. This makes restraint the preferred method when work allows sufficient setback from the edge.
Understanding Fall Arrest Systems
In contrast to restraint, a fall arrest system is engineered to safely catch a worker after a fall has already begun. This system is a reactive measure, meaning it manages the consequences of the hazard when prevention is not feasible due to the nature of the work. Fall arrest systems are significantly more complex because they must absorb and dissipate the tremendous energy generated by a falling body.
The primary components include a full-body harness, a specialized connecting device, and an anchorage point designed for high-impact forces. The harness is designed to distribute the arresting forces across the strongest parts of the body, such as the pelvis and shoulders, minimizing injury to the worker. Connecting devices often incorporate a shock absorber, which deploys upon impact to slow the fall and reduce the force transmitted to the worker.
The Maximum Arresting Force (MAF) placed on the worker is limited to 1,800 pounds or less. The anchorage point for a non-certified fall arrest system must sustain a static load of 5,000 pounds per attached worker, reflecting the much greater dynamic forces involved in stopping a fall. Self-retracting lifelines (SRLs) minimize freefall distance but rely on an internal braking mechanism to dissipate energy.
The Critical Importance of Calculating Fall Clearance
Calculating fall clearance is a practical distinction separating fall arrest from fall restraint systems. Since fall arrest allows the worker to fall before activation, sufficient vertical distance below the work platform is necessary to stop the fall before the worker strikes an obstruction. This calculation is not required for fall restraint because the worker is physically prevented from reaching the hazard.
Total Fall Distance (TFD) determines the minimum required clearance. The calculation begins with the Freefall Distance (FFD), which is the length of the lanyard or the distance the worker travels before the shock absorber deploys. This is followed by the Deceleration Distance (DD), the length the shock absorber elongates to dissipate energy, often up to three and a half feet.
Calculating Total Fall Distance
Additional factors must be included to account for system dynamics. Harness Effects (HEFF) and stretch, which can account for about a foot of extra distance, must be added to the total. Finally, a mandatory Safety Factor (SF) of at least three feet is included to provide an adequate buffer against miscalculation or variations in equipment performance. If the available vertical clearance is less than the calculated TFD, the fall arrest system cannot be safely used.
Choosing the Right System Based on Work Conditions
The selection between fall restraint and fall arrest prioritizes eliminating the hazard whenever possible. Fall restraint is always the preferred method because it completely removes the danger of a fall and the risk of suspension trauma or impact injury. Restraint should be the system of choice when the work surface allows sufficient setback from the edge.
Fall restraint is feasible on flat roofs or platforms where the worker can perform tasks while tethered at a distance that prevents reaching the perimeter. The simplicity of the components and lower forces make it a straightforward solution for tasks not requiring edge access. Work conditions, such as the presence of a parapet wall or an available overhead anchorage, can significantly influence the feasibility of restraint.
Fall arrest becomes mandatory when the work requires access to the edge, such as during leading-edge construction or maintenance tasks. If the worker must move over the edge or if mobility exceeds the limits of a restraint lanyard, an arrest system must be used. In these situations, the focus shifts to managing the forces and ensuring adequate clearance to prevent contact with the lower level.
Ongoing System Integrity and Safety Checks
The ongoing integrity of both restraint and arrest systems depends on systematic inspection and maintenance protocols. Before each use, workers must conduct a thorough pre-use inspection of all components, including the harness, lanyard, and connectors. This daily check ensures there are no cuts, fraying, broken stitches, deformation of metal parts, or signs of chemical damage.
Beyond daily checks, periodic inspections by a competent person must be conducted at regular intervals or as specified by the manufacturer. These detailed, documented inspections verify that the equipment is functioning correctly and is free from excessive wear that might compromise its strength. Inspection records provide an auditable history of the equipment’s condition and compliance.
A unique and non-negotiable step for fall arrest systems is the immediate removal of all components that have been subjected to a fall-arresting load. Even if the equipment appears undamaged, the forces sustained can compromise structural integrity or shock-absorbing material. Once a fall occurs, the harness, lanyard, and connectors must be tagged, removed from service, and destroyed to prevent future use.