When to recommend lightning protection

[mshields]

I'm doing work in a 4 story building that is part of a hospital. My HVAC counterpart is adding all sorts of equipment on the roof and suggested that I lightning protect it. I reported back that there is no lightning protection system now and that if we were going to "lightning protect" his equipment, it would remiss of us not to advise the client to protect the entire building in accordance with NFPA 780.

What I'm unsure of is whether or not the facility needs it. I am aware that lightning protection is not something that is code required. I know that there are isochronous maps to help but what other criteria would you use to determine if it is required?

thanks,

Mike

 

[bphgravity]

My advise would be to perform a lightning risk assessment in accordance with Annex L of the NFPA 780. There are plenty of free online calculators that do all the math for you. This will tell you without doubt whether or not an LPS is recommended or not.

In any case, surge protection is an absolute must: www.nemasurge.org

 

[charlie b]

This will tell you without doubt whether or not an LPS is recommended or not.

I emphasize that word, because there is no code requirement for a LPS. The NFPA 780 process will tell you whether an LPS is warranted or not. The process looks at the probability that the building will be struck by lightning, taking into account the number of lightning strikes per year in that geographic area (which you look up on a map), the proximity of other buildings and trees, and the geometry of the building itself. The process then looks at the potential consequences of a lightning strike, taking into account the function that the building serves, the occupancy, the dollar value of the contents of the building, and other factors. This part is mostly an owner's call; I wouldn't complete this part of the analysis without speaking with the owner. The final result of the analysis compares these two concepts.

As an example, a building might be in an area with a low risk of a lighting strike, but the owner might decide that the value of the building's contents are worth spending the money on an LPS. I have included an LPS in the design of a military housing building, an admin building, and a weapons storage facility. By way of a counter example, a warehouse building for storing non-flammable materials and that includes a sprinkler system to protect the building itself might not warrant an LPS, even if it is in a high risk area and has no nearby tall buildings or trees that might otherwise shield it from lightning.

 

[mshields]

Great input as usual

Great input as usual

Tell me Charlie - In your opinion, in a hospital, typically consisting of a number of interconnected buildings, is it a given that if you're going to do one of those buildings you really need to do them all?

 

[charlie b]

I think you would. But the analysis that tells you whether an LPS is warranted deals with the structure as a whole. If you have several interconnected buildings, then for the purposes of the analysis it would be a single structure.

 

[bphgravity]

Coincidentally, it just happens to be lightning safety week:

http://www.esfi.org/resource/lightning-safety-safety-enlightenment-518

http://www.lightningsafety.noaa.gov/