Ah, the old fall clearance calculation. I'll be honest with you, this has always been a pain in the ass for me. It always seemed confusing to me. I don' t know why. And if it confused me, there are probably a couple of you out there that are confused by this as well. So, let's learn how to calculate fall clearance.
Fall clearance is a very important calculation because if it's not properly determined, you'll be hitting the ground. Fall clearance calculations can help you select the proper fall protection as well. Let's start with the components of our formula.
1. Total Distance (TD) - This is the total distance from the position of your anchor to the nearest obstruction.
2. Required Distance (RD) - This is the total fall distance with your equipment. The required distance must be less than the total distance or you'll go splat.
3. Lanyard Length (L) - The length of your lanyard. Got a 6 ft. lanyard? You'd use 6 ft. for this portion of the equation.
4. Deceleration Distance (D) - This is the elongation of the deceleration device when it's deployed. For example, the shock pack on your lanyard. It is customary to allow 3.5 ft. for this distance. You can check your manufacturer's instructions for exact distances. (A retractable may only add a foot of deceleration distance, but you should always use the 3.5 ft. when calculating)
5. D-Ring Height (H) - This is the distance from the workers' feet to the harness dorsal D-ring.
6. Extra Clearance (C) - The distance from the obstruction after a fall. You must include 1 1/2 ft. for required clearance and an extra 1 ft. for D-ring movement and system material stretch. So you need to have 2 1/2 ft. clearance to the obstruction.
So the magic formula looks like this...
L + D (3.5 ft) + H + C (2.5 ft) = RD (Required Distance)
RD (Required Distance) is less than TD (Total Distance)
If you have any questions don't hesitate to let us know.