A full body harness fall arrest system is specialized Personal Fall Arrest Equipment designed to catch a worker who has fallen from a height, preventing them from striking a lower level or the ground. Its primary function is to limit the force exerted on the worker’s body during sudden deceleration, which minimizes the potential for severe injury. Using this system is a safety requirement when working at elevations where a fall hazard exists and other protective methods are not feasible.
Defining the Full Body Harness Fall Arrest System
A fall arrest system is an active safety measure intended to stop a fall that has already begun, distinguishing it from other fall protection strategies. This equipment is activated only after the worker is in free fall, making it the last line of defense against a severe injury or fatality. Unlike passive systems, such as guardrails, a fall arrest system requires a direct connection between the worker and the structure. It is also different from a fall restraint system, which physically restricts the worker’s movement, preventing them from reaching the fall hazard.
Essential Components of a Fall Arrest System
The complete personal fall arrest system is often referred to as the “ABC” system, representing its three interconnected functional elements. Every component must be compatible and rated for the forces involved in arresting a fall. The integrity of the system relies on the strength and proper connection of all three parts, from the anchor point down to the worker’s body.
Anchorage
The anchorage is the secure point to which the system connects, serving as the immovable object that withstands the impact of the falling mass. For non-certified anchor points, the Occupational Safety and Health Administration (OSHA) requires that the structure must be capable of supporting a static load of 5,000 pounds per attached worker. Alternatively, an anchorage can be designed by a qualified person to withstand a force equal to two times the maximum arresting force generated by the system. The anchor point must be positioned to prevent the worker from contacting any surfaces or objects below the work area during the fall.
Body Support (The Harness)
The full body harness is the component worn by the worker, designed to distribute the high arresting forces across the stronger parts of the body. Webbing straps are positioned around the pelvis, thighs, shoulders, and chest to spread the load, preventing concentration at a single point like the waist. This distribution is necessary to prevent internal injuries or spinal damage. The harness also ensures the worker remains suspended in an upright posture after the fall is arrested, which is important for post-fall rescue.
Connecting Device (Lanyard and Deceleration Mechanism)
The connecting device links the body harness to the anchorage, and is typically a shock-absorbing lanyard or a self-retracting lifeline. A standard shock-absorbing lanyard contains material that tears open in a controlled manner upon experiencing a fall. This tearing action extends the total stopping distance and time, which reduces the peak impact force transmitted to the worker’s body. The deceleration device limits the maximum arresting force on the body to 1,800 pounds, as required by safety standards.
The Physics and Mechanics of Stopping a Fall
The mechanics of fall arrest involve managing the rapid conversion of kinetic energy into controlled deceleration over a specific distance. The system must limit the distance a worker falls before the arrest begins, known as the free fall distance, which is typically restricted to six feet or less. Once the fall is initiated, the shock absorber deploys to create the total arresting distance—the length traveled from the moment of shock absorber activation to a complete stop. By extending this stopping time, the shock absorber decreases the peak force experienced by the worker, ensuring it remains below the injury threshold.
A calculation called fall clearance must be performed before work begins to ensure the worker does not strike the level below. Fall clearance is the sum of the lanyard length, the full deployment length of the shock absorber, the height of the worker’s harness attachment point, and a mandated safety factor. For example, if a six-foot lanyard is used with a shock absorber that deploys 3.5 feet, the total clearance required, including the worker’s height and safety factor, can exceed 17 feet. If the available distance is less than the calculated clearance, the system is unsafe for use.
Proper Selection and Fit
Selecting the correct harness involves matching the equipment to the work application and the environment, such as choosing materials resistant to heat or arc flash. A proper and snug fit is essential to the harness’s ability to protect the worker during a fall. The leg straps must be tightened securely to prevent the worker from inverting or slipping out. The chest strap needs to be positioned correctly across the sternum to keep the shoulder straps in place. The dorsal D-ring, the attachment point for fall arrest, must be positioned between the shoulder blades to ensure an upright suspension.
Inspection, Maintenance, and Retirement
The fall arrest system requires a program of inspection and maintenance. A thorough visual inspection by the user is required before each use to check for any signs of wear or damage that could compromise the equipment’s strength. Workers must look for frayed, cut, or broken webbing, pulled stitches, heat damage, or any signs of chemical exposure. Any equipment that fails a pre-use inspection must be immediately removed from service, tagged, and destroyed or repaired by the manufacturer. Any component that has successfully arrested a fall must be permanently retired from service, as the forces experienced can cause damage that is not visible to the naked eye.
Post-Fall Procedures and Suspension Trauma
A successful fall arrest immediately triggers the need for a documented rescue plan, as the suspended worker faces the danger of suspension trauma, also known as orthostatic intolerance. This condition occurs because the static, upright position in the harness causes blood to pool in the legs, reducing the return of blood to the heart and brain. Prompt rescue is required, as loss of consciousness and severe medical consequences can occur in as little as 5 to 10 minutes. Workers should be trained on the use of built-in relief straps or stirrups, which allow the suspended person to stand periodically to engage their leg muscles. This muscle activation helps maintain blood circulation and temporarily delay the onset of trauma while the rescue team is deploying.