Sharp edges are primarily what we need to protect against, so what defines sharp?
AS1353.2-1997 (which relates to Flat Webbing Slings) states: "Corners with a radius of less than three times the thickness of the sling, are deemed to be sharp." While AS 4497.2 - 1997 (which relates to Round Slings) states: "Corners with a radius of less than three times the compressed thickness of the sling material are deemed to be sharp."
Given that we don't want to be carrying a carpenter's square and a Vernier Calliper to ascertain if a corner or edge is too sharp to use a synthetic sling, a leading company has developed a convenient way to quickly measure the:
- working width of the sling;
- minimum shackle pin diameter; and
- minimum corner radius for the sling.
The tool is colour coded to the synthetic sling sizes and in the photo above, we can measure the working width using the top of the tool, and therefore the minimum length of the shackle pin that would be used to avoid bunching or pinching. Secondly, if a shackle pin can fit through the hole in the centre of the tool, then the pin is too small/sharp for the sling being used and you will need to use a larger shackle. And thirdly, the arc on the tool has been calculated to be three times the compressed thickness of the round synthetic sling. If the corner of the load fits inside the arc on the tool, the corner/edge is considered too sharp for the sling you have selected.
This means you need to choose a different sling or use edge packing as mentioned in the previous bulletin. Note that so long as this tool is colour matched and attached to the sling it represents, you don't need to measure the round sling thickness as the radius on the tool is already sized accordingly.
There is a second tool for flat slings shown below which includes a simple slot to quickly determine the thickness of the sling.
Much like thread gauges, these gauges are designed to be carried together and the operator determines the correct gauge based on the slot width.
The operator then places the cut-out corner against the corner the sling is wrapped over or around to determine if the radius is too sharp (see below).
Synthetic slings are just as safe as FSWR and chains when used correctly. These tools are a brilliant innovation, which will no doubt decrease the number of incorrect sling and shackle choices as well as ensure edge packing is used where required.
This article was originally published in CICA - Vic/Tas Branch's Crane Safety Bulletin #228.