Should a giant steel framed human aquarium be earth bonded?

[Deuce]

I have a large, portable steel framed tank. approx 6m x 2m x 2m. It is used for actors/models to perform in for a variety of productions.

For many years now, I have had conflicting advice about whether or not it should be earth bonded. The initial response is "it's a giant steel structure, bond it!!". But then invariably someone else comes along and points out that, should the tank itself become energised, the people in the water within the tank would become part of the return to earth - the current would flow through the tank and them. If it was not bonded, as it is by design insulated, they would be ok. At least until they tried to leave the tank.

To date our solution has been to be super cautious of anything that could even present the possibility of bringing current to the tank itself. But how do we make a once and for all decision on whether it should be bonded without any professional consensus of opinion?

 

[Deuce]

Surely bonding would create a path?

However it's connected to earth would create a path - the question is whether its safe to create a path through the tank.

 

[StephenRowley]

If the tank was bonded I doubt anyone in side it would see any current flow in fault condition as the current would find the path of least resistance to ground though the nice conducting water.

But really this needs someone who a expert in the field of swimming pool safety

 

[markythesparky]

The one constant is that wherever the tank goes, 30ma RCD is the standard.

The tank is always sat upon a butyl membrane, so it's isolated.

If it was TT'd, of course that is a sound path to discharge current. But if the clamp is at the base of the tank, and a live lamp collapses and hits the top of the tank, the current would flow down through the tank and the water and through the people inside it surely. In that scenario wouldn't it be better that it was left isolated?

The 30mA RCD is the key. It will disconnect the supply before the current gets to a dangerous level (50mA). If you didn't have the TT, then the tank would remain live and the RCD would not operate. That is until someone or something created the earth path.

Which do you think is safer?

 

[PEG]

Nice clean water is not a good conductor

I think the additional information,increases my belief that this needs a specialist,risk assessment.

Next,we will be told that these performers are lowered in this tank,using an electric crane,and i can think of half a dozen RA issues,on that fact,alone.

 

[Deuce]

Do you have some photos maybe?

 

[markythesparky]

If the tank was bonded I doubt anyone in side it would see any current flow in fault condition as the current would find the path of least resistance to ground though the nice conducting water.

But really this needs someone who a expert in the field of swimming pool safety

Don't run
Don't jump
Don't bomb
Don't spit
No petting
......

 

[PEG]

Don't run
Don't jump
Don't bomb
Don't spit
No petting
......

That's 5 out of 6 of my previous post's RA list

 

[Deuce]

The 30mA RCD is the key. It will disconnect the supply before the current gets to a dangerous level (50mA). If you didn't have the TT, then the tank would remain live and the RCD would not operate. That is until someone or something created the earth path.

Which do you think is safer?

You just opened up another sphere of debate we have had before. If isolated the performers remain safe, so long as they don't connect with the ground or some other earth point. So they will be ok if the fault is detected and power removed. However, if the tank is earthed they will definitely be subject to current until the RCD reacts, on the assumption that all RCD's are going to react - which isn't the case. It's a fact some have their breakdown moment after their most recent test.

 

[Marvo]

Don't run
Don't jump
Don't bomb
Don't spit
No petting
......

Just watched the video....Not sure we should rule out petting so quickly.....

 

[Deuce]

Nice clean water is not a good conductor

I think the additional information,increases my belief that this needs a specialist,risk assessment.

Next,we will be told that these performers are lowered in this tank,using an electric crane,and i can think of half a dozen RA issues,on that fact,alone.

To be honest all water is pretty crap as a conductor. "Clean" water isn't a conductor at all. The water in the tank is probably cleaner than your tap water, but will still conduct - albeit quite poorly.

 

[StephenRowley]

But the tank water I would hope have a chlorine or other water treatment in there. Which would massively increase its conductivity to better than that of human body.

What does the tank sit upon? It may all ready inadvertently have a path to ground though the ground it's self.

 

[Marvo]

I think the water conductivity is a moot point. This installation would be treated as a special location defined for bathrooms or swimming pools in the regs. I don't know the finer points of the UK regs but I'm inclined to agree with an earlier post suggesting a risk assessment and appropriate mitigation and management of risks be performed for every time it's used.

 

[Deuce]

But the tank water I would hope have a chlorine or other water treatment in there. Which would massively increase its conductivity to better than that of human body.

What does the tank sit upon? It may all ready inadvertently have a path to ground though the ground it's self.

It's dissolved solids, particularly minerals that increase conductivity. TBH I don't know to what extent chlorine does, but yes we use chlorine.

It sits on a 1mm rubber membrane.

It's not just about the water though. The performers could be in contact with the steel frame itself. Or the steel base of the tank.. Of course the steel is certainly a better conductor than us fleshy beings!! But adding the submersion in water of all parts does add an unusual angle to this problem.

 

[Strima]

Without seeing it set up and doing some testing we’re just stabbing in the dark.

 

[Deuce]

I suppose I should add, that clearly this is not a standard application or problem. It's a very unique thing - and the world is all the more richer for having such things.

My goal is to get to a point at which I'm confident that the best solution for safety is in place. As it stands, with the divide in opinion on this, that certainty isn't there. My personal view is that it should be earthed, as it minimises risk overall. Albeit, under certain unexpected conditions it could be said it would have been safer if it wasn't.