Vapor Opening 1 : An opening through a tank shell or roof that is above the surface of the stored liquid and that is provided for tank breathing, tank gauging, fire fighting, or other operating purposes
NFPA 780 Standard for the Installation of Lightning Protection Systems, 2008 ed. http://www.uscg.mil/Petaluma/TPF/ET_SMS/Manuals/NF PA_780.pdf, (Std: Instll of Lightning Prot Sys - Amer) {347 NFC}