Rigging failures

[lync]

youOn Thursday I was removing a mature Elm, infected with Dutch Elm Disease. Approximately 70 ft tall, with a DBH of 40 inches. Riding in a 60 ft Bucket the top was brushed out without incident.
Working my way down to about thirty feet I was chunking down one of the large leaders, the sling holding the block in place failed, and a piece about 4 ft long and 20 inches in diameter freefell causing minor damage to the terf. No one hurt, no other damage. I replaced the sling and went back to work dropping pieces of the same size if not larger without incident.
We were using 3/4 stablebraid bull rope, 2 ton arborist block, portawrap, and a tenex loopie sling on the block. The failure took place where the sling was choked around the leader, at the point where the parts of the sling crossed. The ground man did let the rope run, but stopped the load before it hit the ground. According to the green log chart this piece should have weighed about 500 lbs. In my opinion the rope , block, and block sling were rated high enough to handle this load, even keeping in mind that the block and sling take a 2x load when the load is decelerated. The sling shows some normal wear, but appeared to be serviceable.
I would appreciate any input, although without you actually being there it difficult to determine the true cause.

Has anyone had any rigging failures?

Corey

 

[P_woozel]

4-5 years ago I was removing a decent size cottowood with another climber, he was rigging on the ground had used him to hold many of the large tops i'd done before, i told him to put the porty on the tree, I hung a 1-ton stainless block, put the rope in 9/16 stablebraind and told him to take 2 1/2 wraps we were taking maybe around 1000# thats on the way outside, so anyway I face it up ty the rope backcut it tops running smooth, real smooth, I look down and the porta-wrap seems close, in fact its getting closer ???? fast I move before it takes my head off. Jamie had put the porty on with a 1" tubular sling on a choke. That explains why the wrap was cruising skyward.

 

[BigJohn]

What size loopie sling was it? 3/4 inch rope seems a bit overkill on that wood. I'd a 32" diameter on a true blue half inch with a 5/8 dbl. sling. Where and how you had these tied off play big part in load factors. Also cycles to failor with the sling used. Perhaps if you used a smaller diameter lowering line with more stretch you would have had less shock at the pulley and sling. You have to look at all the detail. The diameter of the lowering line, the sling, the pulley sheave diameter, placement of the block, placement of the lowering line on the load, distance of fall-length of rope out. Attention to all these little details is key to success.

 

[P_woozel]

Bigjohn, were you using the 1/2" line for 500# in a negative block angle or positive. It seems if you were slamming on the block 1/2" is a little light, though certainly the rope would be the weak link as it should be.

 

[lync]

Sling was 3/4 tenex . I know system was overkill but my company buys items that can handle both medium and heavy loads. Less equipment to buy ya know. The piece I cut loose was directly above riging point, I would say it dropped 12-18 inches before the bull line took the load. I'm leaning towards the cycle to failure theory, since I don't know the age or history of the sling.

Corey

 

[BigJohn]

Yeah I would say, That sling should have taken that load in most any circumstance. Let this be lesson, looks good but may not be good, take nothing at face value.

 

[Stumper]

Erik-Strange about the gasoline -Nylon and Polyester are both supposed to be resistant---which doesn't mean immune but.... less than 25% strength loss.

 

[Nickrosis]

I mis-tied a small chunk, and it landed in the ground cover below. Could've been bad, but it reinforces the point of double-checking things. I was also ready to get outta that tree....