Shock loading safeties

[Aaron S.]

Hey everyone. I was just sitting here wondering if there is any info or a video on the effects of different weights or lighting instruments shock loading safeties?

I have always been told that the less space there is for something to fall the less force is put on the safety. But, I constantly see 80#-100# ML’s with a 36” safety loosely connected around a pipe. No wraps to take up the slack. If that ML should fall would the safety be able to catch it?

 

[DaveySimps]

Chicago Flyhouse has some nice videos that relate to this. You are correct, generally the less distance an object can fall, the less force is applied when that object abruptly stops. To answer your question, it really depends. First of all, it is often difficult to find a WLL on a lighting safety cable, as very few ever come with that marked on them. Different size wire rope and clips are sometimes used, which change the rating. Also, how the cable is secured to the fixture and the pipe makes a difference. What sort of force and in what direction it is applied to the hardware all effect the rating of the safety.

The Chicago Flyhouse Inc

Chicago Flyhouse is a specialty rigging company primarily servicing the entertainment, multi-purpose venue, retail, church, and museum industries.

www.youtube.com

~Dave

 

[Aaron S.]

Chicago Flyhouse has some nice videos that relate to this. You are correct, generally the less distance an object can fall, the less force is applied when that object abruptly stops. To answer your question, it really depends. First of all, it is often difficult to find a WLL on a lighting safety cable, as very few ever come with that marked on them. Different size wire rope and clips are sometimes used, which change the rating. Also, how the cable is secured to the fixture and the pipe makes a difference. What sort of force and in what direction it is applied to the hardware all effect the rating of the safety.

The Chicago Flyhouse Inc

Chicago Flyhouse is a specialty rigging company primarily servicing the entertainment, multi-purpose venue, retail, church, and museum industries.

www.youtube.com

~Dave

Thanks Dave, I’ll check out their videos.

 

[Ancient Engineer]

I was taught long ago (back when I was Junior Engineer instead of Ancient Engineer...) that you should always consider a lighting safety to have a zero WLL.

Early on I was taught that once the rig was focused we'd lower it and adjust up the safties as much as could be resonably done.

The idea was that the old Colortran and Mole-Richardson instruments we used had a similar mass to an average household refrigerator.

F=ma holds true on this planet at least, and the opportunity to reduce the "drop" was good logic.

The whole zero WLL thing came to a head much later when a theater I had done some rigging at decided to hang some subwoofers from the first house electric...

Using safety cables...

Which eventually worked the cables through the ferrules (with some brown-note help from the subs).

Gravity, as if it were some kind of physical law, finished the job by lowering the potential energy of the sub to close to zero by relocating it to the floor, gratis.

Well I got called to the pad and interrogated. Fortunately I had taken a good set of "last day status" photos which showed that the subs were added after my departure...

 

[Aaron S.]

I was taught long ago (back when I was Junior Engineer instead of Ancient Engineer...) that you should always consider a lighting safety to have a zero WLL.

Thank you for the response. I guess my next question. And I am by no means an engineer that’s why I’m asking. If we assume a safety has a Zero WLL why use one at all?

 

[Ancient Engineer]

The idea being that it isn't meant for a "working" load.

That its function in life is as a one-shot shock load.

You should never suspend anything "working" with one.

They should also be PMed regularly to find defects.

I went in a theater once and as part of my mandate PMed the safeties and over 10% had DQs.

Spring bails that didn't close and kinked cabling being the major culprits. Frays and broken cabling being minor, but present.

 

[Aaron S.]

The idea being that it isn't meant for a "working" load.

That its function in life is as a one-shot shock load.

You should never suspend anything "working" with one.

That was my understanding. And I have never used a safety to hang something with. I guess I will have to take a look at some videos and do some math to answer my question. Just didn’t know if anyone had a link to some info. I will start with the Chicago flyhouse videos.

 

[Catherder]

Resident rigger @egilson1 posted this video a while ago. Might also be helpful.

Shock loads video

So I created a short video about shock loads. It’s only 10 minutes long and discusses what shock loads are, and how to calculate them.Enjoy

www.controlbooth.com