BillConnerFASTC
Well-Known Member
Any details?
Affixing screen to truss
- Thread starterfredthe
- Start date
@BillConnerFASTC I was one of the touring IA assistant electricians with "Buddy Holly The Musical" around the corner at The Shubert. Many of us were hanging around outside, prior to a matinee possibly, when smoke belched out of The Music Box's front doors followed moments later by fire engines racing past. Our Local One production electrician was also the production electrician for "Lettice and Lovage" in The Music Box. The New York Fire Department took exception to little things like CD80 96 x 2.4 Kw racks raining down on them from the grid. I believe this was the fire that outlawed nylon slings for such purposes and brought about the insistence upon GAC-flex fireproof flexible slings. "Lettice and Lovage" featuring the two Maggies Smith and Tyzack, was sold out to the walls. The fire department ventilated the building extensively, they hung work lights and kept right on running shows. My wife attended a performance only days later. As we shared the same Local One production electrician we were kept pretty much in the loop.
Toodleoo!
Ron Hebbard
Jay Ashworth
Well-Known Member
@Jay Ashworth Yes. It was the fully loaded CD80 96 x 2.4 Kw. racks raining down through the smoke from the grid that particularly annoyed the fire fighters. Our IA Local One production chief electrician was also their production electrician thus we were kept well in the loop. In the IA tradition, our Local One production electrician was Jimmy (Something beginning with an 'M') Junior. His father was Jimmy Senior. In addition to those two shows on Broadway, young Jimmy was also the production electrician for the North American tour of "Starlight Express" that was simultaneously touring Canada and the U.S. in 1990. I was able to catch the in, out and a follow spot call while Starlight played Kitchener / Waterloo's Centre In The Square when I returned from Broadway. Kitchener / Waterloo is in IA 357's jurisdiction. @derekleffew Was this the "Starlight" tour your mate was with when he went from "heels to wheels"?
Toodleoo!
Ron Hebbard
Ok, finally getting back around to the post. Below are 2 images of slides from my training presentation. The first is a temp/strength curve for aluminum 6061-T6 truss. The second shows the average temp of a building fire, and how steels strength is reduced by heat. Take a look, and continue reading below. Not noted is that the melting point of nylon is about 473 degrees Fahrenheit.
The first think to clarify is that I am a fan of redundancy, but it has to be done properly so if needed it will actually work.
Second clarification is to delineate between a building fire or a specific threat source like a fixture/pyro fx. There is no question that a flame fx or well focused Sharpy can melt a synthetic spanset. But let’s focus on the building fire side.
As the slide shows the average building fire is 1100 degrees farhrenheit. The 1/8” wire rope you hung your screen with now has a breaking strength of 680 pounds. And although this might be above the load of the screen, it’s possible the fire is a lot hotter that the 1100 F degree average. If it was at 2000 degrees F we now have a breaking strength of 200 pounds.
What about the aluminum truss itself. Aluminum has a melting point of between 1080-1205 degrees F. So is the truss still even there let alone holding the payload? How about the screen material? Or it’s aluminum frame? Is the electrical cable?
The truth is in a building fire, our equipment will likley burn with everything else. The truss will fail, the wire will burn, the steel wire rope will be so brittle it will fail.
From Harry Donovan’s Entertainment Rigging - “A theatre fire in Branson, MO lasted 15 minutes and melted the 1/8” GAC, and made the ¼” brittle and it broke.”
I have a bigger issue using climbing slings for rigging due to the difference in how they are designed and tested than because they might melt.
But that’s just me 2 cents worth.
Ethan
The first think to clarify is that I am a fan of redundancy, but it has to be done properly so if needed it will actually work.
Second clarification is to delineate between a building fire or a specific threat source like a fixture/pyro fx. There is no question that a flame fx or well focused Sharpy can melt a synthetic spanset. But let’s focus on the building fire side.
As the slide shows the average building fire is 1100 degrees farhrenheit. The 1/8” wire rope you hung your screen with now has a breaking strength of 680 pounds. And although this might be above the load of the screen, it’s possible the fire is a lot hotter that the 1100 F degree average. If it was at 2000 degrees F we now have a breaking strength of 200 pounds.
What about the aluminum truss itself. Aluminum has a melting point of between 1080-1205 degrees F. So is the truss still even there let alone holding the payload? How about the screen material? Or it’s aluminum frame? Is the electrical cable?
The truth is in a building fire, our equipment will likley burn with everything else. The truss will fail, the wire will burn, the steel wire rope will be so brittle it will fail.
From Harry Donovan’s Entertainment Rigging - “A theatre fire in Branson, MO lasted 15 minutes and melted the 1/8” GAC, and made the ¼” brittle and it broke.”
I have a bigger issue using climbing slings for rigging due to the difference in how they are designed and tested than because they might melt.
But that’s just me 2 cents worth.
Ethan
kicknargel
Well-Known Member
Well. . . sure, everything will fail eventually. But given this info it still seems that the nylon sling will fail first. At 1100 degrees, the nylon is long gone, while the steel is still within a 3:1 design factor (which is too low a factor anyway) and should remain unbroken. And at 475 the nylon has failed, but the aluminum is at half strength (hopefully within its design factor as well).
As a follow-up, we ended up doing a combination of the above. Two slings (one on each side) from the truss to the bottom of the screen frame (they happened to be the correct length) and then load-rated zip ties to fix the screen to the truss. Very secure and stable, and we had backup safety cables for the zip ties though the load on the ties was minimal.
Thank you all for your valuable suggestions and input!
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