What does a third mate do?

On a merchant marine vessel, the third mate is part of the deck department and is typically the fourth in charge of the ship. Traditionally, as the third mate, you are the safety officer and your duties are to oversee the watch both at sea and when docked, ensure that the crew observes all safety protocols, and oversee safety inspections of things like fire extinguishers and lifeboats. Your responsibilities are to lead any emergency responses necessary on the ship, such as fighting fires.