Lightning protection of chimney

[thorpe16]

We are upgrading boilers for an institutional ordinary structure and they mentioned they've had lightning stikes to the stack. We recommended a whole-building protection, but the client came back and said they wish for only the stack. NFPA 780-08 doesn't really define if only the stack can be protected without the rest of the building. Can we protect only the stack?

 

[LarryFine]

Can we protect only the stack?

I believe it depends on the height of the stack vs. the radius and height of the rest of the building. The 'cone of protection' will not cover anything above/beyond that cone.

Whether that coverage is required, I don't know. It's what we pro's call a "design issue."

 

[charlietuna]

Lightning protection requires some design to properly protect a structure. I have heard of installations drawing lightning due to improper engineering. Without a "UL Listed" label the installer risks a large liability.

 

[thorpe16]

lightning protection

lightning protection

Thanks for the info!

 

[bphgravity]

A complete lightning protection system is likely better than a partial lightning protection system, but some lighting protection is most definetely better than no lightning protection.

If the client only desires protection at the stacks, using methods outlined in Chapter 6 of the NFPA 780 and/or section 4.8.8, which ever is more applicable, would be your best bet.

 

[weressl]

We are upgrading boilers for an institutional ordinary structure and they mentioned they've had lightning stikes to the stack. We recommended a whole-building protection, but the client came back and said they wish for only the stack. NFPA 780-08 doesn't really define if only the stack can be protected without the rest of the building. Can we protect only the stack?

Yes you can and often only the stack is protected. As others mentioned a high mast lighting will protect a fairly large area underneath. (150' radius rolling inverted ball cone.)

Protection is a misleading term to use, because what the NFPA 780 lighting system design performs is actually attracting the lighting. Protection is the somewhat succesful result of trying to have the lighting travel on a predetermined path, eg. the 'lightning protective' conductors. Of course everyone knows that in case of a direct hit the induced currents in the adjacent electronics will fry those without sophisticated surge protection.

Even when surge protection provided you can still fry your gear. Since the magnitude is unpredictible, surge protection design relies on a statistical number to strike an economic balance between the cost of the equipment and what the customer is willing to pay for surge protection. (Hence the 'damage protection' monetary clause on the devices. Something along the lines: you are covered up to $50,000 against damage.)

 

[bphgravity]

Protection is a misleading term to use, because what the NFPA 780 lighting system design performs is actually attracting the lighting.

That is actually a little misleading. The presence of an LPS or lack thereof does not induce, prevent, or in anyway effect whether or not a strike is to occur. In the event a strike is to occur, the LPS provides an attachment point and intentional path to and/or from the earth.

While some are led to believe the creation of upwards streamers is increased by the installation of air terminals, it in no way precludes the attachment of storm leaders.

 

[weressl]

That is actually a little misleading. The presence of an LPS or lack thereof does not induce, prevent, or in anyway effect whether or not a strike is to occur. In the event a strike is to occur, the LPS provides an attachment point and intentional path to and/or from the earth.

Unfortunately you can't have it both ways. LPS is an oppurtunistic system. It presents and object that by the combination of its height and low impedance IS conducive to attract leaders that are continuously 'hunting' for a discharge or attachment point.

The generation of leaders occurs ipso facto.

 

[bphgravity]

If that were true, than only buildings and structures with an LPS would be struck. And, buildings with an LPS would would always have strike attachment on the LPS.

But that is not the case is it? It is a common occurance for a highrise building to be struck along the side of the structure, rather than at the top. Smaller buildings a frequently stuck in the vicinity of much taller structures and surrounding trees.

In short, lightning is going to happen no matter what the conditions or circumsances are occuring on the earth. If and when that strike occurs, providing a path for the surge currents to flow is better than not providing one. There is no "hunt", lightning doesn't and can't seek out its target. End of story.

 

[weressl]

If that were true, than only buildings and structures with an LPS would be struck. And, buildings with an LPS would would always have strike attachment on the LPS..

I did not say that. Under laboratory conditions two structures investigated with the same physical and material features. The one equipped with LPS received discharge at much lower voltage levels than the one without. Among multiple structures with and without LPS the one's with LPS are more often receive strikes.

But that is not the case is it? It is a common occurance for a highrise building to be struck along the side of the structure, rather than at the top. Smaller buildings a frequently stuck in the vicinity of much taller structures and surrounding trees..

WHEN they represent a lower impedance path.

In short, lightning is going to happen no matter what the conditions or circumsances are occuring on the earth. If and when that strike occurs, providing a path for the surge currents to flow is better than not providing one. There is no "hunt", lightning doesn't and can't seek out its target. End of story.

Quite the contrary. Downstream leaders have miriad of ionized branches and the eventual strike or discharge will occur on the ones with the lower impedance paths.