I'm wondering about the amount of pressure required for natural gas (the kind pumped into homes for heating systems) to produce an explosion when exposed to an ignition source. Is there a formula of some sort to calculate this? Specifically, if a town house (row home) were filled up with natural gas, say from a leak, about how much gas would need to leak into the home in order for the entire building to explode (not burn down, but explode), leaving no part of the structure intact? And how much pressure would this gas need to be under? Would the amount of pressure normally provided by the home (as in the amount that regular oxygen-rich atmospheric air is under while in the home) be enough to cause this, or would some sort of additional containment be required to allow the gas to accumulate to such a degree? I'm asking because this was an official story given for such an explosion that a friend of mine was affected by, but there were sketchy elements to the whole event, and I'm trying to figure some things out.