Jamieson, Fausset and Brown on 1 Kings 16:15-18

15-18. did Zimri reign seven days--The news of his conspiracy soon spread, and the army having proclaimed their general, Omri, king, that officer immediately raised the siege at Gibbethon and marched directly against the capital in which the usurper had established himself. Zimri soon saw that he was not in circumstances to hold out against all the forces of the kingdom; so, shutting himself up in the palace, he set it on fire, and, like Sardanapalus, chose to perish himself and reduce all to ruin, rather than that the palace and royal treasures should fall into the hands of his successful rival. The seven days' reign may refer either to the brief duration of his royal authority, or the period in which he enjoyed unmolested tranquillity in the palace.