An able seaman provides a variety of services on a merchant ship. They may be asked to act as helmsman and navigate the boat, use equipment during emergencies, perform maintenance and sanitation, enforce security measures, operate deck machinery, keep watch for obstructions, or handle cargo. Most companies use the definition of this role provided by the United States Coast Guard, which considers able seamen to be any position below the officers that is above ordinary seamen, while also holding a Merchant Mariner Credential (MMC). Able seamen typically work on the deck of a ship, assist other members of the crew as needed, and stop work if they notice unsafe conditions or practices.