You can use dimensional analysis to estimate the energy of a blast,

http://splashurl.com/nujc75s

(I hope this is a school homework right?)

Thank you Bernardo, but I am asking about shock wave parameters, i.e. peak overpressure, positive phase duration and impulse etc. My question is, as we know, if we have spherical blast parameters equations, then hemispherical blast wave paramters can be calculated, by multiplying an enhancement factor of 2 or 1.8 with equivalent TNT charge mass. But in case, we have hemispherical blast wave parameter equations (e.g. Kingery and Bulmash simplified equations), can we use them for the calculation of spherical blast wave paramters?

Hey Aleem! Did you get an answer for your question? I'm also facing the same problem of calculating blast parameters for free field (spherical) explosion.

Also, Could you please explain how you come up with the factors 1.8 or 2?