[spokeshave2]

In its natural state, natural gas is actually odorless. That’s why utility companies inject a substance called mercaptan, which emits an odor that smells like sulfur or rotten eggs. If there’s a very strong smell, you could have a substantial natural gas leak. Leave the area, call 911 from a safe place, and call your utility company so they can send out a technician as well. It’s also important not to smoke or use matches or lighters, because natural gas is flammable.

If the fire rapidly spread to the entire floor, and there was a smell of sulpher.....could be a gas leak and explosion/fire.

Some years ago a "mega-mansion" was exploded, reduced to wood splinters by filling it with propane and touching off the propane/air mixture.

[100American]

That looks like something from pone of the Bourne movies when he offs the German guy and then turns on the gas and puts a magazine in the toaster....

Propane stinks, you would most def smell it!

[greeneyes]

Also I’ve heard it’s important not to turn on the light switch, if the house is full of gas.

[Swordmaker]

If the fire rapidly spread to the entire floor, and there was a smell of sulpher.....could be a gas leak and explosion/fire.

I’ve been thinking the same thing. . . add that the occupant of the apartment was said to have had a drug problem and had been scammed out of numerous valuable works of art for drugs, and given the blowout of the two windows and the complete involvement of his apartment in flames, I’m thinking possible suicide by gas with ignition from some spark source when the gas/air mixture reached ideal conditions. BOOM, the fire everywhere. Meets the description of witnesses.