Safeties on chain motors?

Dagger

Active Member
I see safeties being used on chainfalls all the time.
How common is it to use on motors? When ( certain truss length , etc? ) is it necessary to use safeties on motors?
 
Before GACFLEX steel spansets, often fire marshals would require trusses to be safetied to the motor in case the soft spanset melted in a fire. Some European countries require safetying any trusses flown over the audience to the roof/grid. Others only require that if a single motor failure would overload the remaining ones. (i.E. a truss on 2 motors get a safety, but the same truss on three won't get safetied if removing any motor is still under capacity of the remaining motors.)

Some places are starting to require safties for motors that are not double braked.

In the U.S. I rarely see motors safetied... anecdotally, I am not aware of a single motor failure where the presence of a safety would have changed the outcome.

RB
 
I must have not been part of big shows enough to see safeties on truss with motors.
But the arena , rockn roll , cirque , stadium , corporate shows , hotels, ballrooms , convention centres I have been on, I can say that I have never seen safeties with motors .

As mentioned I only ever seen chainfalls with safety either bypass or to the anchor.

You see them on pretty mich every show you do?
How would one safety a truss in ex. an arena once truss reaches trim height? ( aerial lift? Only see them used in an arena once - when the chain fell out of the bag)
 
I've safetied a line array suspension frame over a prototype aircraft - we hoisted the array in the conventional way and then the riggers went up in a lift to add basket steel over the beam to the array frame. If the hoist brake failed the array would slip about 4 inches and the hoist would simply sit on the array frame. The P.I.C. said "I don't care if you drop it on the CEO, just don't hit the plane."
 
And this is what I see - a high school copying it - with "not for overhead lifting" loadstars and a radio transmission tower. Just crap.
There was a question in another forum regarding how to convince another interested party that using 120v Cable hoists to fly a video wall was a bad idea. Seriously, there are people that need to be "sold" on the idea that using the cheapest materials and methods has some kind of drawback.

This is why I think we've made things like electricity too safe. Not enough people can directly relate to personal injuries, deaths, or structure fires due to electrical hazards - there haven't been any spectacular incidents in recent *mass memory*. Ditto for pyro or lasers. Rigging? It's more safe than not because riggers have science, statistics, and best practices on their side. Spectacular rigging failures are rare in the news for a reason... and that means folks that Really Don't Know ask questions where they think the answers are expensive, over the top, or are an impediment to the fulfillment of a mission or vision.

So I'll say this again - until there are days worth of news coverage from a technical failure of rigging, power, pyro or lasers, some people in control of our work in production crafts will be complacent and not understand the reason we don't have problems is because *people have already died* and we've learned from what happened so it won't need to happen again.
 
Well, the Station was certainly a major pyro failure. And the Indiana fair truss failure. And a trio of pit filler collapses a few years ago. Outside of US a number of assembly large loss of life fire incidents reported, but all seem to be the lack of more than one means of egress.
The Station fire was 20 years ago, out of site, out of mind. The Indiana State Fair roof collapse was blamed on weather in the eyes of most folks - an act of God. That there was no engineering study done for the way it was erected that year, or the use of Jersey Barricade (K-rail) guy ballast instead of the permanent guy points, etc was disclosed but in the minds of the public, was an unfortunate weather circumstance (that led to Jim Digby founding the Event Safety Alliance). Pit fillers? I read about those here, but they didn't make the national news.

What I'm saying, Bill, is that whatever happens needs to be of cataclysmic proportions to get the attention of people who have become safety-complacent and that the cause(s) need to be squarely identified as taking unnecessary risks with life and property. Don't get me wrong, I don't want anyone hurt or killed, but you and I have been around long enough to understand the *psychology* of denial on the part of those who make decisions about the way we work. And these days it takes spectacular, network & social media attention grabbing failures for folks to take notice...

ps. I still have the Thorton-Tomasetti and Whitt Associates reports from the Indiana State Fair roof collapse. There's a whole lotta blame to share.
 
Occasionally we will send out steel when we do really big calls. It is really “situational” in a sense that we always send out gakflex but sometimes steel slings are requested.
 
In the last 10 years, I think I've only put steel safeties on one truss. And that was as an additional basket from the motor, not as an additional tie off to the building. The gist I get is that this seems to be more the habit on big televised production, than it is for live event crowds. Of all the failures I've seen personally, the could only have been prevented by a separate safety off to the building, after the structure has been lifted. I don't believe I've ever seen a failure that could have been prevented by an additional safety around the truss to the motor.

That being said, "I've never seen a problem here" is a really bad basis for not putting a safety feature in to place. I recall reading something years ago about the dangers of shock load and a loose steel safety shearing through a truss, but I can't find it.
 
That being said, "I've never seen a problem here" is a really bad basis for not putting a safety feature in to place.

I think there's a valid argument to be considered here that adding safeties to rectify something that hasn't been an issue in practice has potential to create more problems than it solves. I'm thinking about what happens when someone thinks they removed all the safeties but forgets one and starts to lower the truss to the floor. Not exactly the same method of failure, but not unlike that video wall that fell recently in Vegas when it was being lowered while one of the motors wasn't responding. IIRC, eventually the brake on the motor failed and the resulting shock load caused the Verlock wire rope grips used for leveling the video wall to shear the wire rope dropping the wall to the floor.

The circumstances are also a little different if we're talking about 1- and 2-point loads as opposed to a 6-7 pt hang. Single point line array hangs? I prefer to see a safety, particularly in a long term install where the motors may move only a few times a year. In permanent installs we also encounter more variety of attachment and connection methods. The motor could be fine but the attachment of the chain to structure could fail.
 
Ok, let me pose this question to the readers. How often do properly installed hoists fail?
 
We probably cannot know since all are not reported. But some have. I recall a speaker fell on and killed a tech at the concert venue that use to be in Chicago south burbs. I've stuck a few others in my files - not sure I can find. A "super grid" at some venue in Jersey is one I recall because I knew of consultant. We have that video wall in Vegas.

For me, enough that loads should not be lifted, lowered, or even held over heads by a chain motor.
 
New Jersey - Boardwalk Hall, Justin Timberlake/Christina Aguilera?
 
Most of the rigging failures I have heard of were truss and structure failures, a few overloaded point failures, etc. Boardwalk hall was an overloaded point, not the motor itself. The only speaker killing someone in near Chicago that I am aware of, one rolled off of the stage onto a guard. Motors not running are usually a human error problem. In every one of those failures, a safety would have had no impact on the outcome. As for Bills distaste for truss and motors, what is the alternative? Counterweight fly systems? (because those are certainly not accident free either) For temporary installs, outdoor structures, and multipurpose spaces, chain hoists are the best option.
 
The Boardwalk hall collapse was a truss failure due to overloading. Not a hoist failure.

The Las Vegas LED wall collapse was operator error in not recognizing they didn’t have control of a hoist.

Electric chain hoists are extremely robust devices with a significant history of reliability. In 2011 and survey was done by PLASA to try and determine a failure rate of hoists in the entertainment industry. The issue discovered as a result of the survey was that a majority of the reported hoist failures were not due to sudden unexplained mechanical failure but do to human failure during operation, particularly overloaded hoists.

The point is there is very little actual data to support that belief that electric chain hoists fail often enough to require secondary static safeties.
I’ve attached the results page of the study.l for reference. Keep in mind over 80% of the “failures” reported were actually human error.
 

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