Tank Lightning Protection 1

[Schwatzernov]

I would like to know whether tank having thickness > 5 mm with platform and handrail around the top perimeter of tank needs air terminal for lightning protection or not ?

In case a tank alone without handrail, it is clear that the tank itself is self protection but with handrail around top perimeter of tank, is sepearate air terminal required or not since the thickness of handrail is normally less than 5 mm.

 

[dpc]

This will determined by local codes. Other variables you haven't told us include tank material, what is in the tank, and other location-specific factors.

In general, a steel tank does a pretty good job of handling lightning, if it is well grounded. It's the non-metallic structures and tanks that are more of a problem.

David Castor

http://www.cvoes.com

 

[Schwatzernov]

Thanks dpc,

The tank is the raw and service water storage tank made from carbon steel used in power plant.

From my experience, even though the tank has handrail above, still there is no separate air terminals above the top of tank and seems to be the correct design. However since NFPA780 and as well the IEC standard does not mention specifically whether the separate air terminals are needed or not when handrail presented around the top of tank perimeter, someone has opinion that the handrail has less thickness than that required by standard, 4.8 mm, so the additional air terminals are required to be installed at the specific interval along the handrail and one 6 m air terminal at the middle of top of tank. Is this necessary ?

 

[7anoter4]

According to NFPA-780 :
4.6.1.2 Metal parts of a structure that are exposed to direct lightning flashes and that have a metal thickness of 4.8 mm (3/16 in.) or greater shall require ONLY connection to the lightning protection system.
4.6.1.3 Such connections shall provide a minimum of two paths to ground.
This is recommended for all "ordinary buildings".

 

[7anoter4]

The building you have to protect it is the tank and it is protected.
You don't have to protect the handrail but you have to bond it to the main lightning protection grounding that means the tank. If it is welded to the tank roof you are o.k. See NFPA-780:
4.20.2* Roof-Level Potential Equalization. For structures exceeding 18 m (60 ft) in height, all grounded media in or ON the structure shall be interconnected within 3.6 m (12 ft) of the main roof level.
4.19.1.1 Bonding shall be required if there is likely to be a sideflash between the lightning protection
system and another grounded metal body.
4.19.1.4 Metal bodies located in a steel-framed structure that are inherently bonded through
construction shall not require further bonding.
The handrail could be damaged by strike but you could fix it easily, I think.

 

[Schwatzernov]

7anoter4

Thanks for your advice, it is very useful for me.