There are many factors to consider when evaluating available fall clearances for an overhead anchorage. Factors of influence in determining the total fall distance of a system include:
Free Fall Distance: The vertical distance traveled during an incident and before the fall protection system beginning to arrest the fall. Free fall distance should be limited to a maximum of 6’-0” unless special considerations are made in the development of the complete personal fall arrest system. Activation distances are limited to 2’-0” for self-retracting lifelines.
Deceleration Distance: The vertical distance traveled from activation of the fall protection system to arresting of the fall. Deceleration distance varies by lifeline device, including between different models of self-retracting lifelines, and shorter deceleration distances typically result in larger arresting forces.
Activation Distance (SRL): The amount of line paid out by a self-retracting lifeline (SRL) from the onset of a fall to the point where device begins to apply braking or stopping force.
Maximum Arrest Distance (SRL): The total distance traveled from the onset of a fall to arresting of the fall; typically the activation distance plus the deceleration distance when there is no slack in the lifeline.
Stretch Out: The additional fall distance resulting from body elongation and flipping of the D-Ring during an incident. Plus considerations for elasticity and improper fit of the body wear.
Swing Fall Distance: The vertical drop in the height of a user’s D-Ring during a swing fall incident, as measured at the lowest point during the swing. Swing falls are pendulum-like motions that occur during and/or after a fall which initiates from a position that is horizontally away from the overhead anchorage.
Safety Margin: A clearance factor of safety between the lowest extremity of the user’s body and the level and/or obstruction below after arresting of the fall and stretch out.
Additional considerations that must be made:
Falls that initiate when a worker is in a crouched, kneeling or lying position require additional fall clearances. The industry standard is to consider an additional distance of 3’-0” as part of the stretch out in total fall distance calculations when initiated from a crouched or kneeling position and an additional 5’-0” when initiated from a lying position.
Slack in the lifeline will occur when the anchorage is not high enough above the user and will increase the total fall distance. This should be considered for self-retracting lifelines when the anchorage is not adequately elevated to keep the entire device above the user’s D-Ring. When utilizing shock absorbing lanyards, lifeline slack can be extreme.
A grey area in regards to verifying available fall clearances is that total fall distance calculations are variable between the Occupational Safety & Health Administration’s regulations (OSHA), the American National Standards Institute Fall Protection Code’s best practice specification (ANSI Z359), and device manufacturers published user instruction manuals. Note, only the OSHA regulations are binding by law.
Below is a reference table which expounds upon this. What this table tells us is that you should consult a safety professional if you are considering an overhead anchorage and have fall clearances less than 10’-0” and/or cannot locate the anchorage directly overhead of the user.
And, that if your safety management program mandates ANSI compliance instead of just meeting OSHA regulation, you better reevaluate all those overhead anchorages where available fall clearances are less than 10’-0”.
Notes for the Table Below:
The Table applies to single user overhead anchorages with self-retracting lifeline devices only.
The table assumes that anchorages are directly overhead of the worker.
The table assumes that users are in a standing position, without crouching, kneeling or lying down.
The table assumes that the anchorage is high enough above the user to avoid slack in the lifeline.
The table assumes a maximum combined weight of 310 pounds for the user and their tools.
The maximum arrest distance is equal to the device activation distance (free fall) plus and the deceleration distance.
The maximum value of 2’-6” for harness contribution must be considered when body wear selection is not controlled or known.
See critical assumptions. Swing drop distances must be added to the minimum total fall distance.