https://i.imgur.com/JH1lsGZ.jpg
Method 1: Fireball[]
Window height: 16 px or 1 m
I'm going to assume the fireball diametre to be the debris demolished in the middle, considering the fact that the fire continued to spread, and the ring of fire is the aftermath, not the initial fireball.
Fireball diametre: 199 px
Fireball radius: 99.5 px, or 6.22 m
Y^0.4 = 0.00622
Y = 3.051237138e-6 megatons, 3.051237138 tons
Non-nuclear explosion, divide by two, 1.53 tons, Building level+
Cable was in the epicentre or so, so he should scale.
Method 2: Destruction[]
The destruction completely demolished the building.
We can take the building to the left as reference.
Height of the roof: 33 px or 2.06 m
Height of one storey: 49 px or 3.06 m
Width of the building: 135 px or 8.44 m
We see from the debris that there are at least 2 storeys. Adding the height of the roof that's 8.18 m.
Assuming 80% hollowness, and 8 j/cc fragmentation
8.44*8.44*8.18*0.2*1e6*8 = 9.323053568e8 Joules, 0.22 tons, Small Building level+
Assuming 3 storeys cuz the one on the right has 3.
8.44*8.44*11.24*0.2*1e6*8 = 1.2810650624e9 Joules, 0.31 tons, Building level
My Opinion[]
I think the 0.31 ton-end is the best, since the debris looked a lot more than 2 storeys, while the fireball one is assumed radius.