Like all other miracles of the Bible, one cannot appeal to natural processes to explain a non-natural event. We cannot appeal to physics or any of the scientific fields to explain a miracle. The explanation is simply not in the natural world. Apart from the power of God, there was no way to explain how these men survived such an experience.
Nebuchadnezzar immediately came to the correct conclusion. He attributed this to the reality, power, and presence of God. How could he possibly do otherwise? When Nebuchadnezzar saw the fourth man in the furnace, he made a rather interesting statement, “…and the form of the fourth is like the son of the gods.” NOT “like the Son of God,” as it is rendered in many translations.
I cannot help but wonder how Nebuchadnezzar knew what a son of the gods would look like. I think the idea is simply that Nebuchadnezzar saw an angelic figure, a being he immediately recognized as being different than the others in appearance. Whether or not this was an angel or a theophonic manifestation is unclear and a matter of some disagreement among scholars. What is clear from the language is that Nebuchadnezzar did not recognize this fourth figure as the third member of the Triadic Unity. It is suggested by Dr. Fuller that Nebuchadnezzar was identifying the fourth person as the son of the Babylonian fire god Iz-bar – dā-mêh lə-ḇar- ’ĕ-lā-hîn.
From the Pulpit Commentary, “The suggestion of Dr. Fuller [is], that here in bar we have not the word for "son," but rather a truncated form of [the Babylonian] god of fire, Iz-bar….”
While I find this an intriguing possibility, I think we must recognize the fact that when Shadrach, Meshach, and Abed-Nego are released from the furnace, Nebuchadnezzar did not thank his god Iz-bar for their deliverance. Rather, he thanks the God of Shadrach, Meshach, and Abed-Nego
“who sent His angel and delivered His servants who trusted in Him, and they have frustrated the king’s word, and yielded their bodies, that they should not serve nor worship any god except their own God! Therefore, I make a decree that any people, nation, or language which speaks anything amiss against the God of Shadrach, Meshach, and Abed-Nego shall be cut in pieces, and their houses shall be made an ash heap; because there is no other God who can deliver like this.’”