Security on a bridle

[premix]

Hello I'm still french so I want first to be clear with the words.

 

I call a security the sling we put near the hoist (in order to prevent a failure from this hoist or its sling) after the truss is in its final position.

 

If it's not clear please tell me

 

Now the question : for a bridle, how do you secure your hoist ? My idea is to put this security on the nearest beam to the hoist ?

 

Do you have any idea or suggestion ?

 

Thank you all for your answers.

 

If something is not clear, tell me and I will add some drawings.

[ontoprigger]

Usually the Safety is to bypass the hoist, if the hoist is not rated for suspending loads above people, if your hoist is a D8+ or BS7906 type A then unless specified in the rigging plan and/or the risk assessment then a safety is not required.

 

If you do not have a hoist that is suitable or its specified then the bypass can go from the point supporting the hoist to the truss.

 

one of the easiest ways to do this is with a device designed for the purpose that clips into the motor chain and an 'O' ring that the motor is also attached to.

 

 

The most important part is to make sure if the motor did fail there will be no movement in the suspended load and the only real way to achieve this is to remove the load from the hoist, so effectively dead hanging the load from the alternate point of suspension

[indyld]

I understand the question, although it does raise a bigger discussion about secondary suspension. Chris Higgs and the PLASA riggers advisory group have stuff worth reading on this.

 

The main thing is that the load should not move IF the primary suspension failed and the safety was to take the load. Therefore using only one beam on what was originally a bridle isn't the answer.

 

What is depends on why the safety is designed into the system and what it's supposed to be guarding against.

[premix]

Hello everybody and thanks for the answers.

 

Indeed I have to suspend square trusses with four hoists at least. So I think that if one hoist fails, the truss will not move with a safety (well taut) on one point.

So in this case (see the drawing ), do I have to also make a bridle for the safety ?

 

 

http://i613.photobucket.com/albums/tt216/premix6/forum%20rig_zps95l5z2ks.png

[Jivemaster]

Remembering that I'm NOT familiar with legistation in your country:

 

The Lift should be just that, for lifting. Then the load needs hanging from points at trim height. Then the bridles from the lift could be secured with wire rope or chain bypassing the chain hoist, as the safety.

 

I know of one company with one hoist. Things get lifted, then secured to fixed points, then the hoist removed and used at the next point.

[david.elsbury]

One hoist? That sounds like they have more time (and money to spend on labour) than sense!

[Jivemaster]

I was surprised, but it was true. It does serve as an extreme example that you can have lights "up there" on fixed support not on the hoists.

[premix]

Yes that's right I first have to look to the french legislation but it doesn't describe how to secure a bridle.

 

Jivemaster thanks for your answer, I understand your solution but for my show I have to rig seven square trusses with at least four hoists each and I have to do about 30 bridles so I have to find the simplest (more simple ?) solution

 

Thanks.

[ontoprigger]

Hello everybody and thanks for the answers.

 

Indeed I have to suspend square trusses with four hoists at least. So I think that if one hoist fails, the truss will not move with a safety (well taut) on one point.

So in this case (see the drawing ), do I have to also make a bridle for the safety ?

 

 

http://i613.photobucket.com/albums/tt216/premix6/forum%20rig_zps95l5z2ks.png

 

 

 

 

With this method the load would swing, so you would need to create a second bridle point as a safety, but as I said before, the idea of the safety is to bypass a hoist not rated for suspending loads over people. Most of the standards for suspending equipment do not take the entertainment industry into consideration and are meant for fixed installations or industrial uses where the load would not be left hanging on the hoist.

 

As you are in Europe you can adopt any of the member states standards or codes of practices as long as it is equivalent to or better than any in your member country.

 

So as France does not have anything on entertainment rigging and suspending loads above people you are able to use VLPT SR2.0 the German standard for entertainment rigging or BS7905 and BS7906 the British Standard and code of practice.

 

If you do opt to do this you need to follow it fully and all the equipment in the rigging point would need a 10:1 or 8:1 factor of safety depending on which of the standards you follow but as long as you use a D8+ or BS7906 Type A hoist then you will not require the safety.

 

If you do not have a suitably rated motor, a device like this can be used, its rigged from the same points as the motor and fixed to the truss, so when you are all done the suspended load is lowered onto and thus bypassing the motor.

 

http://2rent.se/webshop6-2/4-rigging-1069177837/accessories-302751169/2000035-detail

 

 

but remember, for loads suspended above people the factor of safety for all of the rigging equipment needs to be increased to either 8:1 or 10:1 depending on the standard you are following.

[Seano]

The Lift should be just that, for lifting. Then the load needs hanging from points at trim height. Then the bridles from the lift could be secured with wire rope or chain bypassing the chain hoist, as the safety.

 

This is a wee bit dogmatic and somewhat outdated. There are lots of hoists out there designed for lifting and subsequently suspending the load. Those built to BS7905 Category A for example, or to BGV D8+. And it can be perfectly acceptable to use others for the purpose subject to risk assessment.

 

Speaking of risk assessment - there is the downside to what you suggest. The operation of lifting the load, suspending it from a separate suspension, disconnecting the hoist and de-rigging it is all hazardous. When you risk assess an operation involving work at height the first and best control measure to make it safer is to eliminate it altogether. You could infer from that a clear legal duty not to undertake unnecessary work at height.

 

I know of one company with one hoist. Things get lifted, then secured to fixed points, then the hoist removed and used at the next point.

 

What things do they lift? Not a lot of long lighting trusses I hope? Or box trusses (as in the OP's case)? Or line-array PA systems?

 

 

 

 

 

Yes that's right I first have to look to the french legislation but it doesn't describe how to secure a bridle.

 

Really you need to be discussing this with a professional rigger familiar with the regulation that apply to your gig, and more importantly familiar with who interprets the regulations and enforces them. Venue policies. Local authorities. That kind of thing.

 

I have to rig seven square trusses with at least four hoists each and I have to do about 30 bridles so I have to find the simplest (more simple ?) solution.

 

The secondary in your drawing is something that we used to see a lot in the UK music industry. It was never good practice, but there was rarely time to do a better job and because policy varied so much from place to place the riggers doing the job didn't consider the secondary really necessary anyway so were not keen to put a lot of effort into making it really nice. Things are much more uniform across the country now, and we do not put as many secondaries on. When we do, we usually make a better effort to make them good.

 

Is it your decision whether to have a secondary or not to?

If so, for example you might decide that they are not necessary because you can use BGV D8+ hoists. Or because you can use enough hoists that one hoist failing would not cause the truss to be overloaded or to fall.

 

In UK English, this is what we mean when we say a hoist is "redundant". For example a line-array PA weighing 600kg hanging on two 1000kg hoists. If one hoist fails, the other can still hold the load and nothing is overloaded.

 

Are the hoists on your box trusses redundant? What happens to the truss etc., if you take one away? If the answer is 'nothing', then do you need a secondary?

 

Ok. Here is another suggestion for you... (Blurry napkin-cad sketch follows...)

 

http://www.deepsoup.f2s.com/BR/bridle_bypass.jpg

 

Do you have access to the truss at height? Do you need to visit anyway, perhaps to focus lights? A possibility that has not been suggested so far is to use an 'O' Ring (also called a 'master link' in English) at the apex of the bridle. And from there hang your secondary as well as the chain of your hoist. Sometimes you may see this done with a long steel which just gets wrapped round and round the truss to take up slack - this is not good practice. Obviously it is much nicer to have some adjustment, a clutch-chain probably, and a proper pick-up on the truss.

 

But at the risk of being really boring, I'll say this again: If you need help to make this decision, you need to get it from a professional rigger - ideally one who is familiar with the venue where your event will be, but at least familiar with your region.

 

Good luck.

 

 

Edit to add:

I just realised I have drawn you a sketch of the same suggestion 'ontoprigger' made just up ^ there.

If you do not have a suitably rated motor, a device like this can be used, its rigged from the same points as the motor and fixed to the truss, so when you are all done the suspended load is lowered onto and thus bypassing the motor.

 

http://2rent.se/webshop6-2/4-rigging-1069177837/accessories-302751169/2000035-detail

[indyld]

Seano is correct, we did used to do similar things with 'safeties' back in the day, including towing them from a single bridle leg point and wrapping the slack out around the truss, cable and the rest. This was, a suggested, because it was often the only way to put in a secondary with the kit on site and the time available. Safeties had become a de facto 'thing', following the even older days of leaving the truss on the motors (or the genie towers - remember that?). The safeties created more truss walking on the in AND the out, in an era when harnesses were still viewed as a personal choice by some. Trouble was, 'it must have a safety' was often just another of bit of dogma rather than something that the riggers really believed would ever be tested meaning that 'good enough' was just that. Someone said we have to put a secondary point in (steel all the way) and so we'll do that as best we can with the kit that arrives on site. If you consider how many motors or points you've witnessed actually fail and compare this to something like a chain spill, you can see why riggers might seem more obsessed with chain bags than with the secondary arrangement.

 

The reason I bother mentioning all this is for anyone reading the thread to be aware of current thinking on the topic AND how things change over time. As has been suggested in this thread, this is why the question of why things are requiring a secondary point, what is it actually doing or required to do? etc. And we are back to risk assessment again...

[Jivemaster]

The first question should be; are the hoists properly rated for supporting the load over people? If they are, then that offers a solution without safeties. If they are not then there IS a need for safeties.