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