This article, dated today, indicates that there is still no "official" cause of the explosion...yet.
An investigation into the cause continues, the Minneapolis Fire Department said. The blast, around 8 a.m. on Jan. 1, tore apart a building that housed 10 apartments and a grocery on the street level.
I have almost zero knowledge of fire/explosion investigative techniques but common sense tells me that if there was a natural gas explosion it should be fairly quick and easy to come to that conclusion.
Natural gas is lighter than air. This I do know. If the explosion occurred on the second floor and there was a volume of gas sufficient to destroy the building then I would have to assume that someone (actually several someones) on the upper floor would have reported a very definite odor of gas prior to the explosion.
I would also have to assume that whatever source was leaking natural gas in a sufficient quantity to destroy the building was still leaking (or capable of leaking if gas service was restored) after the fire was extinguished. I would think that it would be a fairly easy matter to locate the source of the leak even after the building was destroyed. For instance, I would think that the gas main entering the building could be isolated and a compressed air line connected to the line leading into the demolished building. The compressed air leaking from the open connection would be pretty easy to find/pinpoint in the rubble. In other words, I don't think that the explosion, resulting fire, extinguishing agents and the collapse of the building would shut off the leak. The leaking pipe should still be there. One caveat: I suppose it is possible for an explosion of this size (and the resulting destruction of the building) to
cause a break in a gas line.
I would also assume the the gas company would not be so publicly forceful in
their denial that the building had zero issues with gas leaks if it were not demonstrably true or if there was any chance that such a statement could easily be proven false.
Becca Virden, a spokeswoman for CenterPoint Energy, said there were no natural gas leaks in the system and that the utility received no reports of a suspicious odor before the blast.
I am also under the impression that it is probably not routine protocol to have the FBI involved in the investigation of an apartment explosion/fire.
Greg Boosalis, supervisory special agent with the FBI in Minneapolis, said the investigation is continuing, but at this juncture there is no evidence of terrorist activity. Boosalis said the FBI has been assisting Minneapolis officials in a "support role."
It has now been the better part of a week since the explosion occurred and the authorities have yet to rule one way or another. It just seems to me that this would not be very difficult to rule on, one way or the other, within such a span of time.
Fire Chief John Fruetel said Thursday that investigators are focusing on a gas explosion as a possible cause due to the nature of the debris field and because some witnesses spoke of an odor. However, he added the exact cause may never be determined.
Please note the parsing of the words..."some witnesses (may or may not be occupants) spoke of an odor (may or may not have been a combustible gas odor which may or may not have been detected prior to the explosion)." What he did not say: "Building occupants smelled gas prior to the explosion." Also (and I ask this from total ignorance on the subject), how common is it to never determine the cause of a building explosion and under what circumstances does it become impossible to do so?
But, as I said earlier, I am not an authority on such matters so these are my opinions based solely on my own speculative judgement.
