I too have worked a couple gasoline vapor explosions that caused significant damage. The damage was much as you described. Walls bowed and heaved as well as detached. The one thing that I can say is that both the events I worked yielded many positive gasoline samples and in fact one only needed to walk into the houses and the odor was overwhelming. To say that the damage you describe with a gasoline vapor event is rare is likely accurate. To say it can't happen is simply not true. It can. I do realize nobody has said it can't happen. The damage you describe would lead me to believe it was along the line of what us folks who do not know as much as Gerald would describe as low order for lack of a better term. I did not get the sense that you had shattering and splintering type damage in your description rather pushing/shoving/heaving type damage.

Dave