DC's first volume of Firestorm was ended prematurely after only 5 solo issues. The young story was finished as a Flash backup.
I must tip my hat to Conway and Milgrom for creating one of DC's most powerful characters. Despite being under used and under appreciated Firestorm has been at the heart of big stories, most recently Forever Evil.
As Stein and Ronnie are fused as Firestorm, Ronnie has complete control over the body and Stein merely has a back seat. Stein is there primarily to aid in teaching Ronnie the science he needs to know to wield his awesome powers. Stein being a nuclear physicist, he knows a few things about science and manipulating subatomic particles.
Firestorm, somehow, causes nuclear changes in atoms to transmutate them from one element to another. Changing neutrons can cause an atoms nucleus to be unstable but it is the number of protons that give an atom its identity. Carbon has 6 protons in its nucleus, oxygen has 8 and uranium has 92. It is unclear of Firestorms method of causing transmutation. Is he causing nuclear decay? Is he, somehow, chaining subatomic particles at will? Both? Neither? It is unclear exactly how his powers work. In the real world you cannot simply turn a taxi into water, as shown below. A taxi is made of countless atoms that are mostly metal (remember this comic was written in the 70's) and to turn it into water the metal (mostly iron) has nearly triple the number of protons (26) as water (1 proton for each hydrogen and 8 for oxygen. 10 total). To be a superhero Firestorm must conceal the energy from radiating and harming the public, so he must use his powers carefully.
Join in more Firestorm fun later as I will dissect the science used in the first volume.