I will talk to my Son-in-Law about this, he works for an engineering firm that does things like NG repairs, upgrades, etc.
Sure, until we have some official report (which could take days weeks, months?), it's all speculation. But reasoned speculation, presented as such makes for good discussion, IMO.
There was something like this in Chicago ~ 10 years ago. I'll see if I can find links, but IIRC, that was traced back to a regulator in the supply-line system that failed. The pressure was so high at the home regulators, that the pressure just blew right through them. It was sudden, not an on/off thing where gas had time to build up. People reported that their gas stove-tops had flames jump up like a jet engine (probably already on, I would think a pilot light would have been blown out?).
[edit/add] OK, found a source, longer ago than I though (time flies!) bold mine:
http://www.historyillinois.org/FindAMarker/MarkerDetails.aspx?MarkerID=44
... At 4 p.m. on January 17, 1992, a series of explosions and fires ravaged the River West Community. ... The disaster resulted in 4 fatalities and 18 buildings destroyed or damaged.
Initially the increase in pressure was attributed to a faulty regulator. However, after lengthy investigations, the Illinois Commerce Commission (ICC) and the National Transportation Safety Board (NTSB) determined that a Peoples Gas Company crew was responsible. While doing routine maintenance on gas pressure regulators valves in a vault at Erie and Green streets, the crew failed to monitor downstream pressure when the pressure regulators were off-line. Normal gas pressure of 1/4 PSI soared to at least 10 PSI -- 40 times the normal pressure.
The extreme pressure caused hissing noises in stoves, furnaces, and space heaters. Many individuals shut off their gas service, thereby saving lives and properties.
Based on recommendations by the ICC and the NTSB, regulator valves that once controlled entire neighborhoods were replaced by individual regulators at each building. Increased training for gas crews was also initiated.
So I take from that, that at the time there was not another regulator in each meter? So the crew was working on a regulator that affected the entire neighborhood, with no 'back up' down the line? Scary.
10 PSI doesn't sound like much, not enough to physically blow out a line or anything, but for something designed for 1/4PSI, as they say 40x - that's a lot of gas flame!
-ERD50