Premise
Batman survives explosion. Guy in the middle is not him, as he has a weird belt dangling, so it's the vampire dude escaping the explosion, while Batman says the word detective inside the building as the bombs go boom.
Feat happens in Detective Comics #743. Full context here.
Heights
This doesn't use inverse square law since Batman takes the full brunt of the explosion and walks out of the building pretty okay.
I'll just assume the vampire dude shown in the middle of the explosion is the same height as Batman, 6ft 2inch or 1.88 m.
Calc
The weird vampire guy (Blue) stands 70px tall (2346-2416px).
The explosion (Green) is 1037px long (97-1134px).
1037/70= 14.814285714285714285714285714286x and 1.88*14.814285714285714285714285714286= 27.85086 m diameter. Halve to get 13.92543 m radius
(13.92543)^3*((27136*1.37895 + 8649)^(1/2)/13568 - 93/13568)^2= 0.2170258 tons of TNT (Small Building level+)
Yeah 8-C Post-Crisis DC is prolly not happening anytime soon.
Tallies
Batman ends up in the middle of a big explosion= 0.2170258 tons of TNT (Small Building level+)