I think the authors should change the wording, or language in that link. The point they are making is certainly correct, in that pulling at angles, much of the “force” is being applied horizontal instead of vertical, meaning you are applying less pressure vertically on your load. I think it would be a pretty tough thing to make rules or laws about it. But, I also think its a good thing to have in your mind as you are securing a load. Sometimes its more obvious than other times…
The crazy thing about that link though, is they keep referring to WLL. It sounds like they don’t have a full understanding of what a WLL is. It doesn’t matter if your angle is 90 deg, 45 deg, or 360 degrees… It has absolutely NO bearing on WLL. Working Load Limit, is simply a safety factor, which the manufacture (with guidance from the fmcsa) has determined is an appropriate margin of safety, over when the strap will fail. A 2″ strap (generally speaking) has a breaking strength of 10,000 lbs. With the determined Safety Factor of 3, the Working Load Limit has been determined to be 1/3 of that 10,000 lbs, or 3,333 lbs. Whether the strap is 45 degrees, or 90 degrees, it will still fail at 10,000 lbs…. SF3/WLL, is still 3,333 lbs.
Working Load Limits or Safety Factors, are to account for the un-accountable. Loads shifting… Hard braking… Because nobody brakes the same, because nobody takes every corner at the same speed, there has to be an extra margin for safety added.
Under most conditions, OSHA has determined, that for over-head lifting, a Safety Factor of 5 must be used. For a hoist to lift a 1,000 lb load, it must be built to withstand a 5,000 lb load. The Ultimate Strength of the hoist is 5,000 lbs, but the WLL/SF5 is only 1,000 lbs.