Here's my theory. >>3013401
To increase pressure within the pipes, you would have to increase the gas going into the pipes, or continue pumping gas into the lines at the same rate, and block the exits. Some homes exploding, some not, might be explained by knowing which homes were using gas, and which ones weren't at the time of the explosions. Perhaps, the ones not using gas, allowed pressure to build up in the pipes and explode since the gas had no exit? That would mean the homes that exploded were possibly unoccupied, thus explaining the lack of casualties. So, the source of the disaster would be the central location for the gas pumping, which would have an abnormal increase in gas being pumped into the pipes. You are looking for a central location sabotage or perhaps human error/neglect due to to union troubles causing under staffing or poorly trained newbies running the show.