Replies to This Discussion

Permalink Reply by Jason Brooks on January 2, 2009 at 9:11pm

Not sure what you are asking here. The webbing that we use is rated at 4000 pounds. We use it all the time. What use would you consider as dangerous? We use it for anchoring in a pinch, rescue harness, soft linking, etc.

Permalink Reply by Dave Reed on January 8, 2009 at 3:38pm

No
NFPA system are to be at #9,000 lbs using 1inch webing tied with a water knot (tape Knot) usaually lands around # 8,000
Again your getting hung up broad opinion .
1 inch webbing if used as utility such as to hang edge pro is fine . Even if used as part of a system , it can be made to meet # 9,000 simply by doubling the wraps

Permalink Reply by Jason Brooks on January 10, 2009 at 6:53pm

That's true, I did not mean that we use it as a single piece for anchors. Multiple wraps and multiple pulls are always used to share the load.

Permalink Reply by Ben Waller on February 20, 2009 at 11:04pm

1-inch tubular webbing is rated at around 4,500 lbs when off-the-spool new.
The new 1-inch flat webbing is rated at around 5,500 lbs.

That rating is for a single strand stretched end-to-end.

If you use a three-bight anchor or a wrap-three/pull-two, the anchor sling has 4 legs.
With each leg rated at 4,500 lbs, that means you'll have a rating of around 18,000 lbs for the entire sling, as long as you don't exceed the critical angle rule of 90 degrees or less for the sling angle.

Even a one-bight (loop around an object) is rated at 9,000 lbs (two-leg anchor sling) so it meets the 9,000 lb rating as well.

Now for the water (tape) knot. CMC and other rope rescue data sources all rate the overhand knot at a strength reduction of around 50% of the webbing strength. However, the water (tape) knot is a overhand retrace knot with the webbing doubled. Additionally, the doubled webbing decreases the tight angles that weaken the overhand knot somewhat. That adds back the missing 50% strength - at least approximately.

I have participated in testing webbing slings to destruction using a crane rigging shop's dynamometer to pull webbing loops to failure. Interestingly, we never had a water knot failure. The webbing typically failed at around 5,000 lbs for 1-inch tubular, 8,000 for the 1 inch flat, and 10,000 lbs for the 1 and 1/8 inch tubular webbing.

1 inch tubular webbing is fine for life safety applications if rigged properly.
1 inch flat webbing is a little better.
1 and 1/8 inch tubular webbing is the safest.
Water (tape) knots are safe if properly tied.

Ben

Permalink Reply by TrainingTECH1 on March 14, 2009 at 2:23pm

Here is my take on this.

NFPA is a consensus standard and any good lawyer is going to ask why you didn't use equipment that meets a standard developed by your peers. If a rigging strap has been tested by ASTM and is labled with its MBS, could you use it? I say yes as long as it meets or exceeds the strength requirement listed in NFPA 1983 (NFPA uses ASTM testing methods). But I will go on to say that I would recommend only purchasing equipmet that states it meets NFPA 1983 requirements. Right or wrong it's just not worth the risk.

By the way the requirements for rigging straps is located at NFPA 1983- pg. 24. I don't think there is a standard for typical flat or tubular webbing when used for rigging. Only when it is used in some product such as a harness or strap. Someone else may want to read 1983 a little more thorough.

Permalink Reply by lutan1 on March 15, 2009 at 5:34pm

That's my exact thoughts- though it may be rated, it has not gone through any form of stringent testing (For us, it is an Australian Stadard test).

For my commercial business, I refuse to use any webbing, slings, etc that are not Australian Standard certified. It seems to be a legal minefield that I don't want to cross....

Permalink Reply by SkydiverBC on May 7, 2009 at 4:21pm

Posted above

Permalink Reply by SkydiverBC on May 7, 2009 at 4:35pm

"I have participated in testing webbing slings to destruction using a crane rigging shop's dynamometer to pull webbing loops to failure. Interestingly, we never had a water knot failure. The webbing typically failed at around 5,000 lbs for 1-inch tubular, 8,000 for the 1 inch flat, and 10,000 lbs for the 1 and 1/8 inch tubular webbing."


If the webbing did not fail at the knot, where did it fail? Knots don't fail, they weaken the rope at the entry point to the knot, usually at the first bend after the rope/webbing enters the knot. That's why stronger knots have more gentle bends in them. The figure nine is stronger than a figure eight because the bends are wider, a figure 10 is stronger than a nine (but far too bulky to use in rescues). You stated that the webbing did not fail at the knot, I am curious where and why it failed where it did. Thanks

Permalink Reply by Ben Waller on May 10, 2009 at 2:29pm

The webbing failed rather randomly...

Some of them failed where the webbing was attached to the dynamometer, some failed along a straight stretch of webbing, and some failed about 4 or 5 inches from the knot.

We were happy with the heavy steel attachment points on the dynamometer - I don't remember the exact dimensions, but they were thicker than typical carabiners. They were polished smooth, so there were no edges, burrs, etc, that cut the webbing when it was under load.

Permalink Reply by Ben Waller on May 10, 2009 at 2:35pm

Luke,

If we have to use sewn slings for webbing (tape) instead of being able to tie our own loops, then we'll be forced to use swaged eye splices to create loops in the ends of our ropes instead of tying knots in the rope.

I don't see a practical or legal difference. The doubled nature of the water knot (follow-through overhand bend) makes up for any strength reductions the knot puts in the rope.