approx 4 million btu per ton of tnt
approx 1000 btu per cu ft, so 4000 cu ft of NG per ton tnt
about 9-1/2 cu ft of air per cu ft NG, right?
so, 42,000 cu ft of house for a ton of TNT for NG blast (aka air-fuel bomb)
Say big house, 8 ft ceiling, 4000 sq ft house including basement, etc = 32/42 approx 3/4 Ton of TNT equivalent.
at 50 ft away, about 8 psi overpressure or wind speed like a Fujita F4 tornado ripping thru the neighborhood which is what the damage indicated.
To actually plan for the level of damage seen and to acheive the stochiometric mix at ignition would imply an intelligence way above what the perps obviously are lacking .. stupidity is no defense for murder, esp when evil intended.... concur with charging sentiments of previous posters