Lightining Protection on Scaffolds

[wtucker]

Our company has subbed out construction of a scaffold that runs from grade to the top of a 13-story hospital, on three sides of the building.

It seems to me that it should have lightning protection, but neither the scaffold erector nor our electrical engineer has ever heard of such a thing. I'm particularly concerned about the effect a lightning strike might have on life support equipment inside the hospital.

Thoughts or code references would be appreciated.

 

[bphgravity]

Review Section 4.19 of the NFPA 780 for some guidance...

 

[charlie tuna]

most lighning protection systems require all metallic materials to be bonded--consider what this would cost on a scaffold this size. i have been on jobs where lightning has hit the tower cranes -- only once did it damage the crane(blew out the feeder breaker) but never damaged the building. never forget that lightning is unpredictable --having a lightning protection system does not guarentee the building from lightning strikes. i have seen two buildings with fully certified lightning protection systems get hit and damaged....

 

[dereckbc]

There is a reason your errector or engineer has never heard of such a thing; No one will pay for it. Unless the scafold rises above the height of the building, chances are null it would ever be hit by lightning. You should be concerned with structure, not lightning.

 

[iwire]

I have bonded large scaffolds to building steel in the past not so much for lightning protection but in case the temporary wiring we installed on the scaffolding faulted to the scaffolding steel.

 

[wtucker]

It's for a helipad

It's for a helipad

It DOES go to the top of the building. We're repairing the helipad. The helicopter hangar roof will be the only thing higher--and not by much!

Anchorage for the scaffold has been increased by a factor of four.

I'm concerned about the effect a lightning strike to the scaffold might have on the various life support systems for patients inside the hospital, perhaps near windows. How expensive is a human life?

 

[iwire]

We here at Mike's are all interested in safety.

For example bphgravity spends a lot of his free time researching about lightning and lightning protection systems, he provided some references for you to consider.

That said I have a couple of questions.

Are you assuming the building is more likely to be struck by lighting due to the scaffolding?

Are you assuming that if the scaffolding / building is/are struck by lighting there will be more damage to the life support systems because of the scaffolding?

Let me suggest this, the building, wrapped in scaffolding is now more protected from a direct lightning strike as you have essential built a Faraday cage around the entire structure causing the lightning to run to ground on the exterior of the scaffolding.

By the way, this is a real photo from the Boston Museum of Science, that arc is essentially indoor lightning.

Faraday Cage

 

[wtucker]

I guess I'm thinking the scaffold would present a bigger target than the building.

Mostly, I'm wondering whether the giant Faraday cage we're wrapping around the building might have some electromagnetic or other effect on the electronic life support and monitoring systems inside.

And, lightning being unpredictable and fickle as it is, I'm wondering where it might travel once it hits the scaffold, with all its connections to the building.

 

[bphgravity]

Here is a reponse from a TRUE LIGHTNING EXPERT, Abdul M. Mousa, PhD, P. Eng, Fellow IEEE, BC Hydro, Burnaby BC Canada:

The scaffolding on one or more sides of a building does not materially increase the risk of lightning strikes to the building. This is because it includes many closely-spaced steel columns that rest on the ground and ence can safely carry the current to ground. Even if a side flash occurred from the scaffolding to the building, its impact should be mitigated by the surge protection of the equipment within the building.


Regarding the risk to workers on the scaffolding, safety rules require them to get off the scaffolding and take shelter indoors when a thunderstorm is expected.

Abdul Mousa

 

[boboelectric]

Lightning is it's own domain,man,Look at M.S.H.A.'s in their conclusive investigation of Sago Mine Explosion caused by a strike 2 Miles away.

 

[dereckbc]

Tucker as IWIRE staed we here are very concerned about safety. As Brian pointed out the way in which a scaffold is constructed offers its own protection by multiple closely spaced loops, multiple contact points with earth, and that any strike will be safely directed to earth

If there had ben any problems in the past you can darn well bet Insurance companies and OSHA would have a list of requirements. The only one is workers must vacate during a thunderstorm. That is why the errectors and engineers have never heard of such a thing.

 

[wtucker]

Thank you one and all for your advice.

Even scaffold erectors said they'd never heard of lightning protection on a scaffold but...

We're going with NFPA 780, Sect. 4.19 et seq.: "Metal bodies, located outside or inside a structure, that contribute to lightning hazards because they are grounded or assist in providing a path to ground for lightning currents shall be bonded to the lightning protection system in accordance with sections 4.19, 4.20 and 4.21."

4.19.1.1 says, "Bonding shall be required if there is likely to be a sideflash between the lightning protection system and another grounded metal body."

With all the extra fasteners we installed from the scaffold to the building, we thought a sideflash was certainly possible. We've decided to both bond the scaffold to the building's lightning protection system AND to ground the legs every 60 ft. Best to be conservative. The lightning protection installer told us he'd installed lightning protection on three other similar scaffolds.

Thanks again for the help.

 

[charlie tuna]

it's good you got direction from the lightning protection installer and maybe get it in writing??? years ago we did a sizable job for a large lightning protection contractor actually because he didn't have the manpower to do it!! he once told me that you can very easily make matters worst by guessing at what is the correct method of trying to outguess a unpredictable force of nature. electrical contractors do not have the training for this and "IF" something was to happen(unpredictable) the court officials would make you look stupid during the lawsuite.............

 

[jerrygioia]

Lightning info

Lightning info

I am going to say something that I think you all know, but I didn't read any refrence to it so here goes..
Number one, a building that has lightning rods every twenty feet on the parapit of roof is protected on all sides because from the tip of rod, by the way has a 22 1/2 degree angle, which is called the cone of protection. This cone is from the tip of the rod flaring out to 22 1/2 degrees all the way to the ground level and anything in the circumfrence of that cone is protected from Lightning.
That why you will see in certain areas an airconditioner in the middle of roof with a rod on it because the only way you can protect it is to put the rod 80 feet in the air to include it in the cone.... or more expensive use a Penzoid crystal...















t of his free time researching about lightning and lightning protection
That said I have a couple of questions.

Are you assuming the building is more likely to be struck by lighting due to the scaffolding?

Are you assuming that if the scaffolding / building is/are struck by lighting there will be more damage to the life support systems because of the scaffolding?

Let me suggest this, the building, wrapped in scaffolding is now more protected from a direct lightning strike as you have essential built a Faraday cage around the entire structure causing the lightning to run to ground on the exterior of the scaffolding.

By the way, this is a real photo from the Boston Museum of Science, that arc is essentially indoor lightning.

Faraday Cage[/QUOTE]