John Gill Commentary 1 Kings 16:18

"And it came to pass, when Zimri saw that the city was taken, that he went into the castle of the king`s house, and burnt the king`s house over him with fire, and died," — 1 Kings 16:18 (ASV)

And it came to pass, that when Zimri saw that the city was
taken
That Omri, and the army with him, had got into it, being a place not much fortified, and Zimri not having force enough to defend it against such an army:

that he went into the palace of the king's house ;
into the innermost and most splendid, as well as the strongest part of it:

and burnt the king's house over him with fire, and he died ;
that he might not fall into the hands of his rival, who he might fear would use him ill, and that he might not enjoy the royal palace; though Kimchi thinks that Omri set fire to the palace, and burnt it over the head of Zimri, in which he perished; and this sense the text will bear.