The able bodied seafarer is a rank but it is also a key concept in maritime health and safety. For a ship to operate effectively crew members require the physical and mental capabilities to do their duties, both the routine and those required in an emergency. Illness in a seafarer while at sea poses increased risk for the individual as full medical care is not available. It will also put a strain on other crew members because of reduced manning and the need to care for the person who is ill. Illness at sea can cause both risks and operational problems if emergency evacuation is needed or the ship has to divert to the nearest port to land the ill person. Some infectious diseases and behavioural traits, such as impulsiveness or aggression can also pose a direct risk to other crew members.

 Assessments to identify any health related impairments that can interfere with capability to perform duties and to consider whether there is an increased risk of any serious health problem developing or recurring while at sea and thus reducing the reliability of a seafarer have been part of maritime medical practice for over one hundred years (1). Medical examination and certification is part of both national and international maritime regulation as well as often also being part of the employment practices of ship operators.

 Decisions on fitness can be contentious, as the benefits of reducing risks by prohibiting someone from working at sea have to be balanced against the loss of that person’s skills and their own loss of employment and income. For this reason, as well as because the evidence base on which fitness standards are based is far from perfect, the setting of standards and their application is an area where agreement between different interest groups can be difficult and where a person who is considered unfit has an expectation and a right of a careful review of their health before career-threatening decision is taken.

 This chapter reviews the aspects of work at sea that are important when setting and applying fitness standards, looks at the scope for risk reduction by the use of valid medical assessment techniques, considers the practicality of deciding who is most suitable for a job by reference to some of the commoner medical conditions on which decisions have to be made. It also gives an overview of nature of the national, international and other fitness assessment arrangements that are currently in place.