Chain shackles are best-suited for straight line, single connection pulls because of their U-shape. Anchor or bow shackles have a more generous loop. This allows them to be side loaded or used for multiple connections.
Thursday, September 22, 2016
Are Your Shackles Safe for Overhead Lifting?
Chain shackles are best-suited for straight line, single connection pulls because of their U-shape. Anchor or bow shackles have a more generous loop. This allows them to be side loaded or used for multiple connections.
Subscribe to:
Post Comments (Atom)
10 comments:
I realize that this subject does not exactly float everyone's boat, but despite the seemingly boring subject matter, loading limits and knowing your hardware, especially in something as potentially dangerous as overhead rigging, is vital, whether you like learning about different shackles or not. It is far too often that we hear about terrible rigging accidents in relation to theater or concerts. When bold rigging (such as Kanye West's Stage) succeeds, it's incredible and we praise it, often without realizing the incredible inherent danger in the object. Specifically with Kanye's stage, even a well-designed set can be installed incorrectly or a small detail can be ignored and devastation would follow. There are protocols in place to check all connections, but mistakes do happen. Knowing even basic information like this could lead a rigger to recognize an unsafe connection or a bad piece of equipment and draw a supervisor's attention to it, therefore preventing a potential disaster. It never hurts to know more about safety.
Since I am currently taking the rigging mini, this article stood out and caught my eye. When done correctly, rigging can help create grand effects and has the power to add incredible moments in shows. However, when done incorrectly, improper rigging can be devastating and disastrous. There are all kinds of rules and regulations to avoid rigging mishaps as much as possible. This article was very clearly written and easy to read. Even if I wasn't taking the rigging mini, I am confident that I would still understand what this article is talking about, which is important when teaching about safety. While rigging may not be the most thrilling subject (please no one tell Mr. West I wrote that), it is one of the most important things to know about when working in a theatre. A little bit of safety information can help in a lot of ways.
This type of tutorial/introductory article is super useful to people like me who has never been exposed to the actual rigging practices and would grow a million heads when seeing different types of hardware. I would have no idea which one is suitable for what and how they are different before reading this article. I can see the shape difference and that's it. I do not know what the difference stands for and that's why nobody should hire me as the rigger or the TD.
These kind of trainings seem minor but in fact they are super important even for people who've worked in the field for a couple of years. Some people will probably know screw pin shackles and bolt, nut & cotter shackles are safe to use for overhead lifting, but they don't know why and that's potentially dangerous. For example, these two shackles have different level of security in pin arrangement, and each of them has their own places that require riggers' extra attention. The lack of this knowledge might lead to major safety failure in work. I was wondering if there's a nice way for TDs or PMs to implement basic safety training every now and then without pissing off their employees.
Overhead lifting? Is that live load or dead load? Apparently the shackle knows which one you are doing . . . Like how does the thermos know whether to keep something hot or cold . . . Its interesting that the round pin shackle is not recommended for overhead lifting. It makes sense, as the cotter pin is not meant to resist any side load, whereas the nut and cotter pin would. It is interesting because all of the line sets in the Chosky are hung with round pin shackles. Rather than getting in a pedantic argument about what we should hang line sets with, I want to ask a broader question about rigging recommendations. I don’t mean that we should ignore design loads, and hardware rating, but there still exist situations in which you follow all the hard and fast regulations and you end up with a system that “is not rated”. Rigging depends so much on the common sense usage of standard equipment, that situations arise where common sense is liable. How do we make distinctions? How do decisions change from project to project?
This is actually a rather interesting article, despite its brevity. But it clearly lays out which shackles are best used for what without using confusing language. And their reasoning makes sense- screw pin shackles can untwist but are good for not permanent installations, bolt shackles have a nut that screws in on the outside so it can’t vibrate out and it has a cotter pin for extra safety making it the best option, and round pin are not safe because if you put the load on right the pin could just pull the cotter pin all the way through resulting in system failure. It’s really important to explain things in simple ways and especially in ways that make sense by themselves because then you can actually remember the reasoning. And that is immeasurably important when you are doing something as potentially dangerous as overhead rigging. One small mistake in a long chain of connections can make the whole system fall apart catastrophically. A chain is only as strong as its weakest link.
“Round pin shackles are not suitable for overhead lifting.” Uh oh. Every connection on our fly system from lift line to batten is a round pin shackle. I still trust them because nothing has fallen and Sean West seems to think they are OK. Either way, I am confused why a round pin shackle is not ok in any overhead lifting situation. If it is loaded properly and doesn’t have and axial load, what could happen? The actual clevis pin isn’t going to shear. I suppose that with overhead lifting there is the chance a shackle will see an axial load even if it is not supposed to, but is that reason to say it is not suitable for overhead lifting? I guess it is better to be safe than sorry. But what about in fly system? We can be pretty sure that there will never be an axial load so are we ok using that type of shackle? I hop so.
This shackle is suited for overhead lifting eh? But are allowed to lift live things, or just dead things. I hear the ShackleStop, Patent Pending, safety system is able to detect when somebody is trying to use a shackle to fly a live load and will cease to function immediately. In seriousness, I did feel that this was a relatively concise and informative article on different types of shackles. That being said, I think this article highlights the continued arguments and gray areas in rigging "best practices". Apparently Round-Pin shackles are not suitable for overhead lifting, even though, as others have pointed out, all the LineSets in the Chosky are flown with Round-Pin shackles. I will say, that for whatever reason, Cotter Pins are really un-nerving to me and I would always choose a Screw Pin or Nut Shackle first. I also feel that a Moused Screw Pin Shackle is always a better pick than a Round Pin Shackle, although I am certainly not an expert in the field and have no evidence to back up that claim.
Well... I guess the rigging system in the Chosky needs torn out and replaced. Or maybe not. Under what circumstances would a shackle on one of those line sets see an axial load that would cause any more than minute deflection? Even if that did happen, the cotter pin would surely prevent any slippage. Beyond that, we're talking an earthquake, which presents other problems. However, I very well might be wrong. The article was very educational. I remember learning about the different types of shackles last year in rigging class. I might show this article to Mr. West and see what he thinks. I agree with Chris in that what is considered "safe" and "rated" can vastly change from project to project and site to site. I wish this article had cited a source that they pulled this data from. maybe there isn't one and this is all common knowledge within the rigging community. However, if this all were common knowledge, the Chosky line sets wouldn't use round pin shackles. If rigging is anything, it is convoluted.
I think the norm in theatre has been to use bow shackles, but that’s also because they have been able to serve our purposes. We don’t ever stick to doing the same thing over and over, so we have to work with that as best as possible. Even with the few variations there are for overhead lifting, I don’t think I’ve worked with a chain style shackle. It is understandable that the round pin shackle shouldn’t be used because of how simple it can come apart. But that’s not to say it couldn’t be converted to a bolt, nut and cotter style of shackle, right? If all your doing is changing out the cotter pin for a bolt style then you are still working within the system so long as you use the right style of bolt to attach to, ergo one that is rated for the working load of the shackle.
I’m not sure I believe everything this article says. I know that the shackles used in our counterweight system are the round cotter style. I don’t think that Clancy or Sapsis would use them in rigging if they weren’t rated or safe for overhead lifting. I remember back in undergrad talking about the difference between lifting and dead hanging (where the hardware is used simply to hold weight and not to lift it). Perhaps this is where some of the difference comes in between the practice that we have and what the article says. The type of lifting and stresses applied to the shackle can also determine how much one can lift with it and if it can be used safely. Where I question the article is in how a round cotter shackle is oriented. If the load is vertical on the pin, then there is less of a chance that the pin will come out. If the load is any thing but vertical, it greatly increases the chances of failure.
Post a Comment