NFPA 780 - protection method

[Paul-tecnico]

Hi,
i have a doubt about NFPA 780 article 4.8.2.4 Flat or gently sloping roofs
Flat or gently sloping roofs that exceed 15m(50 ft) in width or length shall have additional strike termination devices located at intervals not to exceed 15 m (50 ft) on the flat or gently sloping areas, as shown in Figure 4.8.2.4(a) and Figure 4.8.2.4(b), or such area can also be protected using taller air terminals that create zones of protection using the rolling sphere method so the sphere does not contact the flat or gently sloping roof area.
I ask you, could we use the rolling sphere method for design our LPS system for a flat roof including the perimeter of such structure or this article is mandatory only for the internal area?
Finally, If we apply "rolling sphere method" to define strike termination position, why do we have to install at 6m-distance - strike termination on the perimeter?

In case it is not possible, we must place our strike termination devices around the perimeter at intervals not exceeding 6-7.6m (20-25ft)?

Many thanks
Please urgent :-(

Paolo

 

[Paul-tecnico]

NFPA 780 - protection method

Dear,
we ask you a short question:

Use "rolling sphere method" instead "Roff types" rules is a choice on charge on designer. So he only can decide how to protect, perform and design LPS. Is it correct?

If any roof has a particular shape, the engineering designer could decide to use rolling sphere method cause this shape is not included in "Roof types" list.

is it correct for you?

Many thanks
Paolo

 

[Dennis Alwon]

I have no idea of the answer however for those who need more I am guessing this is what the op is talking about-- Click here

I moved the op's post from another thread that had more info