As we saw in Game of Thrones S08E05 the queen went on a rampage killing everyone, but is it really possible for a dragon to break the walls like piles of wood?
I am quite amazed, if they can do it so easily then they could have been better used against the White Walkers in S08E03.
My question is: is it really possible for dragons to destroy walls so easily?
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The simple answer is that we all saw it in the show, therefore it is 100% possible for dragon fire to easily destroy walls in the reality that exists within the show.
If you insist on having a real-world physics explanation for how a magical creature in a fictional land can destroy walls, I would suggest that the primary mechanism was the conversion of water to steam.
As a port city, King's Landing would tend to have more moisture in the air and a large amount of water trapped inside and between the brickwork and stonework of the city's walls and larger buildings. The high heat of dragon fire would instantly convert that water to steam, developing a significant amount of sudden pressure that would blast the masonry apart.
Unless, you are a 9/11 truther, you have a real world example of how intense concentrated fire can cause air to heat up and escape the space which contains it at high velocity.
If all the energy of the fire is transferred into the kinetic energy of the expending air and the air delivers that energy with an impact to the walls of a containing structure, the structure can shatter.
Given that the actual fire in a dragon's breath is magical, it's not clear how much energy it can deliver.
