What is a Sling to Load Angle Factor?
Simply put, the sling to load angle factor (SAF) is the multiplier used to determine the additional tension on a sling (or other rigging hardware) when angles are applied. ASME B30.9 and B30.26 recommends that horizontal angles not be below 30 degrees.
How is this figured out?
Mathematically, the length of the sling is divided by the height from the load to the hook. Example: The sling is 10' long and the height is 5', divide the length by the height, for a sling angle factor of 2, which is the SAF for a 30-degree horizontal angle.
How is this done easier in the field?
The problem can be done easier with a shortcut called "The Ten Inch Rule". Once the load is rigged, with a tape measure, find where the sling is 10" high over the load - you do not have to measure the total height of the sling, only to the point where it is 10" above the load. Measure from this point, down along the sling to the attachment point, giving you the sling length. Example: If the sling, from the 10" above the load to the attachment is 16.25 inches long, simply take the decimal point and move it one place to the left, making the SAF 1.625 (or 16.25 divided by 10). Fast, Simple and Easy!
Important to Remember: If your measurement of the sling from 10" above the load to the attachment point is greater than 20 inches, that means the SAF is greater than 2 and the angle is less than a 30-degree horizontal angle. Therefore, the load must be re-rigged prior to picking.