The knowledge base for seafarer medical examinations

The aims of statutory seafarer examinations are:

  • To reduce the risk that health related impairment in a seafarer will contribute to an accident at sea.
  • To reduce the risks of harm to the seafarer themselves, or to others, from their illness.


Medical examinations will not eliminate such risks but will help to reduce them based on a medical assessment that reviews:

  • Whether the seafarer has a current impairment or medical condition that reduces their capability to perform their duties safely and effectively.
  • Whether the seafarer has or has had a medical condition that is likely to recur or become more severe and that may lead to incapacitation or illness such that they would be unable to perform their duties safely and effectively or that may put their own health at risk, given the limitations to medical care at sea.
  • Whether they may put others at risk from a medical condition, for instance by transmission of an infection, while at sea.


Sources of information on risk

The best information about risk will come from well conducted studies on seafarers which investigate the consequences of health related impairment or illness while at sea. Such studies are rare and limited to a few conditions. As all serving seafarers will have been medically assessed prior to starting work at sea and periodically thereafter it is not possible to determine the overall utility of medical examinations using data from the current seafaring population. In addition the collection of valid information on illness in seafarers or on the consequences of health related impairment for safety and performance is difficult and has only been undertaken in limited settings. The knowledge base on seafarer health has been reviewed, as has the information relevant to impairment and safety critical duties at sea. [1]

Studies of seafarers can sometimes be used to support the development of criteria in a few areas, such as the risks of heart attack and other forms of acute arterial disease at sea, the prevention of dental emergencies and tuberculosis transmission. Even for these conditions there may have been changes in diagnosis and treatment, which mean that older studies may no longer be a valid basis for setting criteria, but they may be the only one that is available. In addition almost all the investigation of disease in seafarers has been done in Northern Europe and extrapolation to seafarers from other backgrounds may not be valid.

Given the limited published knowledge base on seafarers the two main sources of information used are individual or collective experience and extrapolation from information collected in other settings.[2] Experience-based sources usually suffer from selective recall, in particular events that have led to difficulties in management are remembered and used to form the basis for subsequent decisions while those that were simple to manage rarely are. Hence the frequency of such difficulties among the overall numbers of those with the same condition may not be properly taken into account. For instance emergencies from biliary and renal stones become apparent but silent stones are also common, hence introduction of an approach that requires imaging and then restriction of all those found to have stones may not be justified as large numbers of people will be restricted for every emergency prevented.

The simplest extrapolations may be from standards adopted in related sectors of work such as the military, for work in remote locations, or for road, rail or air transport.[3] In some of these areas there is better information on the risks of impairment or of illness than is available for seafarers and this can be used as the basis for setting maritime fitness criteria or as an aid to taking decisions about individuals.[4]

Criteria for safe performance of safety critical tasks, for instance vision standards should, if possible, be based on information that is specific to the actual conditions of work and should be used to identify a threshold of performance below which risks are unacceptably large. Such data are not commonly available and little recent research has been conducted to collect them, hence the standards used are inherently conservative and often based on limited studies performed a long while ago.

For many forms of illness there is reasonably good information from general population studies of prognosis.[5] This has formed the basis for setting standards in all forms of transport. However most onshore studies use end points such as death, recurrence or hospital re-admission and this will not necessarily provide useful information on, for instance, the risks of sudden incapacitation. Exceptions to this include studies on epilepsy where seizure recurrence rates are recorded or investigation on the frequency of impairing hypoglycaemia in those with diabetes who use insulin.[6]

As the knowledge base relevant to seafarers is limited and variable in quality many of the criteria adopted are based more on what is seen as a reasonable balance between limitations on employment and risks from impairment or disease, informed by practical or political judgements on the level of risk that can be accepted in those working at sea.

Age in itself is a major determinant of risk but is not readily considered in a formal way for decisions on fitness for work because of employment protection law. Several aspects of visual function decline at a pace that is closely related to age, while the risks of conditions such as arterial disease and most cancers increase progressively with age. The presence of multiple risk factors such as overweight, smoking, lack of physical activity or markers for arterial disease risk also cannot readily be accommodated in a statutory medical certification framework that is based on the presence of a defined medical condition or level of impairment.


The use of knowledge on risk

The prime users for the available knowledge on risk will be those who set fitness criteria nationally or internationally. If these criteria are very specific then those who apply them will have little need for similar information when taking decisions. For many conditions criteria are less specific or depend on the where a person lies on a gradient of risk. Here knowledge of the basis for decision taking can inform the process.

It is also important to be able to explain to a seafarer or to others with an interest in fitness decisions about the knowledge base from which criteria have been derived. Increasingly seafarers and others in the maritime sector want to know the basis on which individual decisions are taken and the validity of the information underlying them. The summaries of risk provided in this handbook can assist with this.


1. Carter T Mapping the knowledge base for maritime health: 3 illness and injury in seafarers. Int. Marit. Health. 2011; 62: 224-235. ...4 safety and performance at sea Int. Marit. Health. 2011; 62: 236-244.

2. Carter T Mapping the knowledge base for maritime health: 2 a framework for analysis. Int. Marit. Health. 2011; 62: 217-223.

3. a) A good new set of driving standards that quotes evidence can be found at

b) The US FAA guide for aviation medical examiners indicates the criteria to be used in aviation 

4. a) Charlton J et al. The influence of chronic illness on crash involvement of motor vehicle drivers (2nd Edition, 2010). Accident Research Centre Report 300, Monash University Australia. 
b) Carter T. Fitness to Drive: a guide for health professionals. Royal Society of Medicine Press, 2006.

5. Prognostic information on many conditions can be found in BMJ Clinical Evidence. British Medical Journal. Subscription service: details at 

6. See ref 4 a.