A third mate (3/M) or third officer is a licensed member of the deck department of a merchant ship. The third mate is a watchstander and customarily the ship's safety officer and fourth-in-command (fifth on some ocean liners). The position is junior to a second mate. Other duties vary depending on the type of ship, its crewing, and other factors. Duties related to the role of safety officer focus on responsibility for items such as firefighting equipment, lifeboats, and various other emergency systems.