Thanks, I'm realy more interested in it as a mental exercise. And while I say bomb shelter, I'm realy more interested in being a gaurd against anouther Katrina, and a safe room while I'm overseas for a month at a time. That said, I've done a good bit of concrete work myself and trust me, I fully understand what 80 sacks are like. On the other hand in my job I have moved and emtied 6,000 pounds of 100 pound sacks of chemicles in a day. Not that I want to repeat it. Anouther concern is that personaly I think most of the quickcrete out there is on the weak side and I have to add portland to it. My slab is 5" thick at the thinest, which when you run the numbers means a 7' span with little to no safty factor. A max 6' span would work. Also as long as you stay 4-6' from the outside of the house the center is non load bearing.
Again, this is a curiosity and it's bugging me to learn more about what he did and how he did it. If I can get the time this summer I'm going to add on to the house with an above ground "bunker" and brick it to look like just anouther room on the house. Slightly more expensive, but probably way better in the long run, and definatly easier to build.