See how to calculate fall clearance distance to ensure that a personal fall arrest system will keep a worker safe if a fall should occur.
Personal fall protection equipment is meant to keep a worker from being injured or killed when working at heights, but it’s not as simple as putting the equipment on and getting to work. In addition to having training on the correct way to wear and use fall protection equipment, some equipment requires some calculations. Personal fall arrest systems require you to calculate fall clearance distance before being used, for instance. Find out how!
Personal Fall Arrest Systems and Fall Clearance Distance
A personal fall arrest system (PFAS) is a system with components like a full-body harness, retractable line, and anchorage that arrests, or stops, a worker from contacting a structure or another level after a fall has occurred. Then, even if a worker falls, the PFAS stops the fall before the worker makes contact with the ground or floor, another level, or a structure.
However, a PFAS can only be effective if it is planned out for each situation. Calculating fall clearance distance is a must before a PFAS is put into use to ensure it will adequately arrest the fall and keep the falling worker safe. Per OSHA, fall clearance distance is the “is the minimum vertical distance between the worker and the lower level that is necessary to ensure the worker does not contact a lower level during a fall.”
If fall clearance distance isn’t calculated, there is a danger of a worker falling and still making contact with a lower level or a structure before the PFAS engages to arrest the fall. OSHA maintains that factors that go into calculating fall clearance distance include:
- Lanyard length
- The height at which the lanyard is anchored relative to where the other end attaches to the worker’s harness
- The distance the worker will travel as the deceleration device absorbs the energy from the fall (i.e., slows it down)
- The worker’s height
- D-ring shift
- A safety factor
Variables needed to calculate the total fall clearance distance, per OSHA, include:
- Free fall distance: This is the distance the worker will fall before the PFAS starts to arrest the fall. This distance has to be 6 feet or less; if this distance will not prevent the worker from contacting a lower level, then a fall restraint should be used. The free fall distance will vary based on the lanyard’s length and where the anchor is set on the harness’s back D-ring.
- Deceleration distance: This is the distance the lanyard stretches in stopping the fall, and it can be no greater than 3.5 feet.
- D-ring shift: This is the distance the D-ring and the harness will move when they move during a worker’s fall. It is usually assumed to be one foot, but it varies.
- Back D-ring height: This distance is measured from the D-ring to the worker’s shoe sole while wearing the harness.
- Safety factor: This measurement is an additional distance added to ensure there is enough clearance between the worker and a lower level after a fall. It is typically 2 feet.
Adding all the above distances gives you the total fall clearance distance. If the calculated total fall clearance distance is greater than the actual distance available, then the PFAS will not protect the worker, and a different form of fall protection should be used.