Magazine article Occupational Hazards

Fall Protection: Establishing the Right Clearance

Magazine article Occupational Hazards

Fall Protection: Establishing the Right Clearance

Article excerpt

How much clearance is required when using a 6-foot, energy-absorbing lanyard? This seems to be very simple question, but the answer(s) may surprise you.

A full-body harness and a 6-foot lanyard are commonly used for worker fall protection. Some people believe that the 6-foot length is somehow chosen to meet the OSHA construction industry regulations for fall protection, 29 CFR1926.502.

Do we use 6-foot lanyards because fall protection is required when more than 6 feet above a lower level? Does a "6-foot" lanyard somehow ensure that the worst-case free fall does not exceed OSHA's "6 foot" maximum allowable?

Unfortunately, a 6-foot lanyard does not ensure conformance to either requirement. The truth is that 6 feet is the most common lanyard length to allow workers a reasonable range of motion from their anchorage.

Required Clearance

In deciding how much clearance we need, we must first agree on what the term "required clearance" means. Referring to Figure 1, we see that clearance calculations can be complicated, and the figure shows three types of clearance:

[C.sub.s] is the "safety clearance" (or "safety buffer"). It is usually specified as how close any part of the user's body is allowed to get to the ground (or whatever else we must avoid striking) when we fall. [C.sub.s] should be at least 2 feet if we separately account for worker and harness stretch ([X.sub.w]). Some people use 3 feet of safety clearance, but ignore [X.sub.w]. I prefer the former approach because, although most harnesses provide 1 foot of stretch or less, some newer "comfort" harnesses stretch more than 2 feet.

[C.sub.p] is the "required clearance below the working surface." It is the distance from the working platform to the lowest point any part of the user's body could reach before the fall is stopped and must include the safety clearance ([C.sub.s]). [C.sub.p] is useful because it is easy for workers to understand and measure.

[C.sub.a] is the "required clearance below the anchorage." It is the distance from the anchorage of the fall-arrest system to the lowest point any part of the user's body could reach before the fall is stopped and must include the safety clearance ([C.sub.s]). This type of clearance is also easily measured or verified in the field. It is most often specified in fall-arrest systems where the user has a fixed-length lanyard connected to his anchorage system and where the anchorage height above the platform can vary. Obviously, the difference between [C.sub.a] and [C.sub.p] is simply the difference between the anchorage and platform heights ([h.sub.a]).

All three types of clearance can be called "the required clearance." We have a potentially dangerous communication problem if someone specifies "required clearance" without clearly illustrating or defining the term.

Free-Fall Distance (FF)

To meet the federal OSHA requirements, the free fall must be 6 feet or less. How do you do this with a 6-foot lanyard?

Figure 1 illustrates a nonrigid anchorage (a horizontal lifeline). Free fall equals the height of D-ring above the anchorage ([h.sub.d]) plus the initial droop of the horizontal lifeline (DAM-DAD) plus the length of the lanyard.

In the case of a fixed anchorage, DAM = DAD = 0, so the free-fall height is simply: FF = [h.sub.d] +[L.sub.y]. Therefore, if we want to limit the free fall to 6 feet when using a 6-foot lanyard, the worker's D-ring must be at the same height as the anchorage ([h.sub.d] = 0). Using the formula in Figure 1:

FF = 0 + 6 ft = 6 ft.

In California, where the state OSHA legislation requires free fall to be limited to 4 feet or less, the fixed anchorage. must be 2 feet above the worker's D-ring ([h.sub.d] = -2 feet) when using a 6-foot lanyard ([L.sub.y] = 6 feet).

Using the formula given in Figure 1:

FF = -2 ft. + 6 ft. = 4 ft.

Deceleration Distance (DD)

To meet the federal OSHA requirements, the deceleration distance must be 3. …

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