lightning protection

[Shavner]

I am currently working on a lightning protection scheme for ordnance facility, and are using mil handbook 1004/6 for guidence. Using these equations i find necessary to install 4-75' masts at the building corners, however whenever I do the clearence arc diagram I feel this is overkill and the building could be protected with two 75' masts and cantenary cable between them. If any one is familiar with theses standards or limitations any input would be appreciated.

thanx

 

[RonShap]

mil handbook 1004/6 seems to be very different than NFPA's document. Any reason?

 

[Shavner]

Main reason is the contents of the buildings. Ordnance facilities require more stringent requirements for direct strikes and possible side flash. Even a little spark could level the building and anything within a few hundred feet of the building.

 

[d23]

Shavner:

I can’t help with your design problem, but I would think that there is a considerable amount of liability attached to this. I would recommend that you keep your entire design info and resource list “in case of.”

Good luck!

 

[peebee]

Are you the system installer?

If not, I wouldn't waste too much time with the design and would instead pass the responsibility off onto the installer, or get them to mark up a drawing for you at this time. They will be taking the final responsibility for the design and installation anyway, and will install whatever they please regardless of your design.

If you are the system installer, well, you probably know more about this stuff than the rest of us out here in cyberspace anyway.

 

[Bob39]

I am looking at a similar situation attempting to protect the munitions unloading/loading area on an AF Base. References I have looked at are, AFMAN 91-201, AFI 32-1065, NFPA APPEND K, AFM 88-9 and ETL 90-6.
MIL-HDBK 1004/6 is not in my library.
You may want to follow-up with those making the request for the protection for this area. Those making the inspection often have there own idea of what is proper or acceptable. In the manuals I can find there is no requirement for a cantenary but the safety inspectors think it should have a cantenary. I don't know about your situation but in mine I have to make sure the protection is adequate and I also have to satisfy the inspectors after it is done.

 

[Shavner]

Yes since I first posted this thread I've learned a lot. from what I've seen there are three requirements for lightinig/side flash protection. first is the mast systm, It basically uses a strike radius of 100' which is a 200' round sphere rolled into the side of the building and down from above as long as the masts stop the sphere within 6-10' of the building it will be protected. the second is grounding of the service entrance and the interior grounds for the storage area, these need to be connected to the secondary protection counterpoise with connection from the primry to secondary counterpoises. the third is for static grounding of all the metalic parts of the building and equipment wuithin the zone of protection. This can get very intensive and as far as the Navy goes it dosent require complete static grounding. The best reference I found allong with Mil 1004/6 is NAVSEA OP 5 design guidelines but I will check the other manuals. The cantanary systems are being used in a case by case evaluation depending on cost, with a cantanery system the number of masts is reduced as well as thier height, however they need to be deflected and the conductor streched between them, again it is all dependant on construction cost.