Page 37 - Occupational Health & Safety, March 2018
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the total forces incurred in the free fall of an average worker. A macabre explanation is that the weight was determined by drop- ping dogs from heights during testing many years ago. Neverthe- less, the regulations have been set forth for decades. In fact, when testing systems under OSHA, you are required to use a weight of 220 pounds (plus or minus 3 pounds) at a free fall of 6 feet [29 CFR 1926 Subpart M Appendix C].
The system would fail the force test if it records greater than 2,520 pounds of force during this test. If the system passes, then, a safety factor of two applied to 2,520 pounds would be approxi- mately 5,000 pounds. However, 5,000 pounds is where many peo- ple stop reading. The “or” clause in the above standard often gets missed or ignored.
But why does it matter?
It matters because the forces incurred during a fall of a 220-pound worker who is utilizing a fall arrest system could be be- tween 900 and 1,800 pounds, not 2,500 pounds. Be mindful that fall arrest systems would have some type of deceleration device that engages after free fall and reduces the force. If we look at the “or” clause in the standard and apply the safety factor of two, it means that in this scenario, our anchor point may only need to support 1,800 pounds of force.
That’s a huge difference from 5,000 pounds. In reality, there may be a number of fixtures in your work area that don’t meet the 5,000
pounds requirement but may satisfy a 1,800 to 3,600 pounds re- quirement—a roof truss or a fixed ladder, for example. By eliminat- ing all potential anchorage points that do not meet 5,000 pounds, we may be making a difficult situation unnecessarily more difficult by not installing (or removing) useful protection.
Don’t Guess at Capacities and Imposed Forces
This does not mean that we can go tying off to things haphazardly. Whether reducing the capability requirement of an anchor point for use with a fall arrest system or increasing it due to a heavy work- er or higher free falls, it is vital that you don’t guess at capacities and imposed forces.
Documentation is vital. Rather than make assumptions, check the manufacturer’s paperwork and technical specifications to see what the exact numbers are. If that doesn’t provide the answers you need, have a qualified person perform the necessary calculations to determine if what you plan to do is sufficient. (Note “plan to do”— this should always be done before beginning the work).
There is a flip side, however, where 5,000 pounds may not be enough. In some cases, especially where horizontal lifelines are used, the forces applied to the anchors, especially at corners or ends, could be large enough such that 5,000 pounds would not work, or at least not meet the two-times safety factor. In those cas- es, it’s important to use a qualified person to calculate the forces on
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