(Click here if drawing doesn't appear above.) 1 Personnel emergency exit hatch. 2 Penetration for VLF antenna (VLF = Very Low Frequency). 3 Equipment entry. 4 Personnel entry. 5 Entry tunnel. 6 High point of roof. 7 Air intake shaft. 8 Air exhaust shaft. 9 Concrete pad for electrical transformer. A Supports for cooling condenser units. B Roof plan. C Grade. D 4 / 1 slope. E Elastomeric roofing. F Section & entry tunnel. G 20% slope. H Non-compacted earth fill.