Introduction and risk assessment principles
Selected medical conditions will be used as examples of some of the practical aspects of setting fitness standards and then assessing individuals based on them. The aim is not to provide a comprehensive guide, but to identify how the potential risks of conditions are evaluated when fitness criteria are being developed, and how the complexities of the condition as it exists in an individual needs to be assessed against such criteria.
Health related impairment can directly have an adverse effect on the safe operation of a vessel:
- Because a seafarer has a stable impairment, such as limited vision, or is unable safely to enter confined spaces because of their size.
- Because they become incapacitated, for instance by a seizure or by an abnormality of heart function while they are doing a key task.
- Safety can also be compromised if they do not have the physical and psychological capabilities to perform emergency duties such as fire fighting effectively
Health related impairments can adversely affect other crew members
- When a person has an infection that can be transmitted under conditions of life at sea or
- Where a person has behavioural traits or mental health problems that put others in danger or impair team working. For TB and HIV see ch. 31.
Health related impairment can lead to increased risk to the individual
- Because there is no immediate access to medical care if there is a recurrence of a disabling condition, a complication arises from a pre-existing condition, or a condition progresses.
- In addition, the incapacity of the individual and any need for other crew members to care for them can adversely affect manning levels.
- Evacuation by helicopter or diversion for an unplanned port call to obtain medical advice can give rise to a range of risks to the vessel and to rescuers.
Even where the condition does not lead to a medical emergency on board,
- Treatment ashore in a foreign port and repatriation are both costly to the employer, who has a duty to pay for medical care while the seafarer is under contract, as well as being traumatic for the seafarer.
- Some conditions such as visual limitations require the seafarer to use corrective lenses to do their work safely
- Many other long term conditions require continuing use of medication and periodic surveillance of the disease and its treatment if risks are to be kept to an acceptable level
- Risk factors for future illness such as obesity, smoking or raised blood pressure may be identified and lifestyle modifications recommended reducing future risks. Their effectiveness needs to be monitored.
All these facets of a medical condition or disability need to be considered when specifying criteria for fitness and the severity and prognosis of that condition in the individual examined also needs to be reviewed before a decision is reached.
For stable conditions it is, in principle possible to assess them in an individual and make a judgement on whether the severity of the condition is such that it puts the individual or others at risk. There can be difficulties with devising test methods that reliably predict the risk at sea as well as concerns about using a trial period of work to see if the are any real problems. The ideal assessment is one such as the lantern tests used for colour vision assessment that actually mimic the task at sea, in this case correct identification of navigation lights in the dark.
For conditions that are episodic or where there are possible complications, then assessment of the individual is only one contributor to the process. Use of the results of studies about the probability of recurrence or complications is also essential. Such date only rarely comes from seafaring or even employed populations and it is often necessary to use the results of studies on the general population, for instance on the probability of a seizure happening at various time durations after the last one, both with and without anti epilepsy medications.
Risk of illness at sea cannot be avoided and the industry unconsciously lives with it. For instance any seafarer aged between 60 and 65 has an approximately one percent change of sudden collapse or of a fatal cardiac event in the next year. Estimates of the level of risk that is currently tolerated form a valid way of establishing the level of risk below which it is no longer worth restricting a person. Current standards in some countries for return to work after seizures and after cardiac events are broadly based on this approach. However, the data on many conditions is insufficient to make this sort of assessment and consensus views of experts may have to be used.
Recurrences of or complications from many medical conditions do not require immediate treatmen,t or the time to the start of treatment will have no adverse effect on risk to life or on the outcome of treatment, for instance dental pain or renal colic will cause distress for the individual, but they are not fatal and provided they receive care within the next day, this will be adequate. In these circumstances work limited to near coastal vessels may be an acceptable option.
For the conditions discussed below, national or other relevant fitness standards should always be consulted before assessing the condition in an individual and taking a decision on their fitness.
Acute infections, because of their short duration and rapid resolution, are generally handled in terms of immediate treatment needs or embarkation screening procedures rather than forming a part of periodic fitness assessments. Infections differ inherently from most other conditions because of their transmissibility by a range of routes, some of which like food or water transmission or droplet and surface contamination by respiratory infections can pose direct threats to others aboard. Other routes of infection such as via body fluids and sexual contact are less immediately relevant. Some chronic infections are included in the criteria used for periodic fitness assessment.
Pulmonary tuberculosis is important because of the risk of respiratory transmission and of progression leading to incapacitation(see ch.30). Chest X rays have been the major tool for detection, sometime linked to Mantoux testing. Now there are also immune assays that are rapid and specific. Judgements can be complex because of the difficulty of differentiating between current infection and the scars or Mantoux test responses from disease that is now inactive. The risk of tuberculosis varies widely between countries and so screening may be selectively directed at those from high-risk areas. Treatment is long term and deciding when a person is safe to return to sea can be a difficult decision.
HIV and hepatitis B both have risks of progression to disabling illnesses and the potential for transmission with body fluids or during sex. (cross ref STD chapter) Both infections can reliably be detected in blood samples, but at a stage when the risk of progression to a disabling condition is low. Those with the conditions can benefit by knowing their status so that treatment and lifestyle modifications are possible. They can, however, easily find they are discriminated against in employment at a stage of the infection when the risks of disability are low and the risk of infecting others in the course of living and working at sea are remote. Preventive measures against hepatitis B by immunisation can eliminate future risks in those without prior infection. Treatment for HIV can greatly delay the progress of the condition, but some medications themselves have side effects that can affect fitness or which require regular surveillance such that work at sea has to be limited to ensure regular access to surveillance. For both conditions fitness decisions depend on the likelihood of progression during the period of validity of the medical certificate.
Decision taking on the fitness to work at sea in a person with diabetes is complex. There is good evidence about the prognosis of both type 1 and type 2 diabetes. Both can in their late stages lead to visual loss, reduced kidney function or neuropathy. However, the increased risk of heart attacks and other forms of large vessel disease can also result in sudden incapacitation. For type 2, early stages are treatable with diet, later supplemented by medication. Type 1 from the start and type 2 when other treatments are no longer effective require insulin. Tight control of blood sugar with insulin slows the development of complications of the disease, but insulin itself causes major safety critical risks from hypoglycaemia when the balance between the dose, diet and exercise gets out of balance. Hypoglycaemia not only can result in collapse and incapacitation, but less severe reductions in blood glucose lead to cognitive impairment and at times to behaviour that includes impulsiveness and risk-taking. With all these complex interactions, how can a valid and fair approach to risk management be developed? Individuals using insulin have to manage their own control by adjusting the dose injected to their pattern of diet and exercise. For some this is an easy task as the dose is stable but for others, as well as in situations where meals may be missed or prolonged exercise undertaken, it can be difficult. Control depends on personal motivation and so is reliant on individual behavioural traits.
First, the presence of any of the long term disabling effects of diabetes needs to be excluded. The stability of the condition in the individual needs to be assessed, preferably from clinical markers such as sequential blood glucose levels and glycosated haemoglobin levels. If the person has already had a major vascular event such as a heart attack, their prognosis will be less good than that of someone who had such an event in the absence of diabetes.
For those with type 2 diabetes controlled by diet alone or by diet and tablets, continued work at sea is usually acceptable, provided the frequency of surveillance is increased, there are no impairing complications of the disease or from the medication used and given an active approach to the management of other risk factors for vascular disease such as weight, smoking and blood pressure. The increased risk of hyperglycaemia and its serious effects does need to be considered when individuals are ceasing to be controlled adequately by either diet of tablets. This risk is higher and may justify either restriction to near coastal work or a high frequency of surveillance.
The risks of hypoglycaemia for different groups using insulin have been established, for some, such as those with type 2 diabetes recently started on insulin, it is relatively low, while for those who have been on it for years, the frequency is higher and awareness of impending hypoglycaemia is reduced. Also the ease and motivation for control and the actual frequency of hypoglycaemia shows considerable inter-individual variation in any one group. For this reason those on insulin have usually been prohibited from all work at sea except non-safety critical tasks on vessels operating near to the coast. There is however increasing information indicating that some individuals can control their blood glucose levels to within close tolerances, and it is now possible to document this with self-recording self-administered testing of blood glucose levels. There is now scope for enabling this sub-set of those using insulin to undertake a wider range of duties and this is becoming incorporated into national standards.
Heart disease is far and away the commonest cause of sudden incapacity and death at sea, as it is on shore (17). Many incidents occur in those who have never had any previously recognised heart problems, but anyone who has had a previous episode of heart disease or has a continuing risk factor such as angina on exertion is at increased risk. There are well established risk factors that determine the likelihood of an initial episode of heart disease, some of these are also relevant to recurrences, but the nature and severity of an initial event also plays a big part in determining the subsequent prognosis.
Thus there are two situations where heart disease risk assessment and decision taking is needed during a seafarer medical examination:
- If there has been no prior event, what are the risks of having one?
- If there has been a prior event, how likely is a recurrence.?
In both cases the implications of an event while at sea for vessel safety, for the individual and for emergency responses need to be assessed. In addition, a previous event can limit physical capability and psychological readiness to undertake physical exertion in an emergency situation.
Within a statutory system of medical fitness decision taking it is rarely possible to exclude a person from employment based solely on an analysis of risk factors that indicate a high probability of future disease. Hence the ‘smoking grease ball’, who is a heart attack waiting to happen , creates a dilemma for medical examiners. It is usually possible to identify lifestyle modifications, such as smoking cessation, dietary control and exercise that can reduce risk and strong recommendations can be made. The scope for sanctions, such as restriction of employment or a period of temporary unfitness, until modifications have been made, may or may not be acceptable depending on the national social contract and legal system.
The position is more straightforward where an event has already taken place, or where a diagnosis of vascular disease has been made. Because large vessel arterial disease is usually widespread, there is considerable cross-over between past events and future risks of, for instance, myocardial infarction, stroke, angina and intermittent claudication.
After an acute incident and its immediate treatment the risk of recurrence of that particular event reduces over the next few weeks, but often against a continuing elevated background risk of vascular disease. It may be possible to predict the likelihood of recurrence from population data and there is now good evidence that, at least over the next one to two years, newer forms of intervention such as stenting or coronary artery bypass grafting greatly reduce recurrence risks. The risk estimates are less well validated for longer periods when more depends on the general progression of the disease process than on the presence of a particular blockage.
Several clinical test methods have been shown to have useful predictive value as means of estimating future risk. These include exercise ECG tests such as the Bruce protocol method – this also has good face value for the subject as they can see how they and their heart performs when they are put through a process of graded exertion. Other measures include left ventricular ejection fraction and ultrasound and isotope based tests of ventricular function.
Given that the industry implicitly accepts the risk of c 1% per year of incapacitation from heart disease in any person of 60-65 years of age, this can be taken as a useful benchmark in decisions on return to work at sea in those who have had a vascular event. Some administrations formally or informally use such a benchmark in decision taking. Thus accepting that if the estimated risk is less than say 1 or 2% per year, a seafarer can return to a full range of duties – provided they are doing their part by a adopting a lifestyle that keeps controllable risk factors under control. Administrations may also accept someone with a somewhat higher level of risks, for instance less than 5% per year, as capable of restricted duties, as a watch keeper where there is a second person at hand to take over in the event of an incident, or limited to coastal shipping where the consequences for the individual in the event of a recurrence can be expected to be less than in mid ocean where no medical care will be available for several days.
Overweight and obesity
An increasing proportion of seafarers have body-weights that are above those considered ideal and this poses difficult problems in relation to medical decision-taking about fitness for work at sea. Overweight is normally categorised by a raised body mass index (BMI), derived from the ratio of weight in kg to the square of the height in metres. However BMI does not accurately reflect the ratio of body fat to other tissue, indeed it can be high in short heavily muscled athletes with low total body fat. It is not a good predictor, except in terms of a broad categorisation between the overweight and the morbidly obese, of physical capability. Other measures such as waist girth have been shown to be better predictors or long-term risks from development of type 2 diabetes or heart disease. Nevertheless it does provide a simple initial way of addressing potential weight problems as they could affect both ability to perform physically demanding tasks and as they influence long term health risks.
Weight control is essentially a matter of balancing food intake against metabolic and physical activity energy expenditure and as such is mainly a behavioural issue, made complex by habituation to the satisfactions of food. This means that it is rarely an easy matter to address during an employment related medical and even more difficult to make decisions about when these determine future employment.
The rationale for fitness standards about weight is first that those who are severely overweight are likely to be incapable of meeting the physical demands of their job, especially those required in emergency situations, and second that this group has a considerably increased risk of sudden or disabling illness prior to retirement age that is likely to either lead to a medical emergency at sea or to mean that their career is terminated prematurely.
Present state physical capability needs to be assessed for each individual. This may be by means of clinical or gymnasium based methods, which usually look at cardio-respiratory reserve (Maximum oxygen uptake (V 02 max) or equivalent treadmill/ step test) plus observed capabilities in terms of strength, flexibility, stamina and co-ordination. Alternatively on-the-job assessment may be made based on abilities to move around the vessel, take part in emergency drills and wear protective equipment such as life jackets and breathing apparatus. Successful completion of demanding training courses in fire fighting or safety of life at sea may also provide evidence of ability.
Where a person cannot meet essential safety needs as established by such investigations they have to be considered unfit until their abilities have improved, usually by a mix of weight loss and improved physical fitness. Where their performance is borderline, frequent surveillance may be indicated. In such cases an increased BMI serves as an indicator of the need for further capability testing and not as the reason for failure.
Advice about the long-term risks from being significantly overweight and recommendations on how to reduce these risks by weight reduction and by other measures can readily form part of a seafarer medical. Frequent surveillance to check that recommendations are being complied with can usually also acceptably be required. However restricting a person or making them unfit is harder to justify if they are currently capable of performing their duties safely and effectively for the duration of the medical certificate being issued. Employers may try to impose arbitrary limits and statutory authorities have tried a range of approaches, but there is no wholly satisfactory approach.
Any rational approach to weight control among seafarers cannot simply rely on measurement and testing. The culture on board the vessel and the attitudes of the family during leave periods to food and to exercise all contribute. Unless employers are ready and able to supply a diet at sea which enables seafarers to eat satisfying meals that are low in calories, then the scope for effective approaches to weight control are severely limited.
Adequate vision is essential for virtually all maritime work. For those doing look out duties an ability to remain vigilant and to discriminate detail, often in adverse visibility has always been essential for vessel safety and navigation. The ability to view instruments, displays and colour coded items is of growing importance and while this may not call for the fine discrimination of a lookout, correct interpretation of form and colour are essential to safety. These tasks can all be undertaken using visual correction from spectacles or lenses. In an emergency at sea visual skills in poor conditions are important, but here visual correction aids may not be to hand or may become damaged or lost, hence some level of unaided vision is also essential.
For most visual tasks the eye works in close collaboration with the parts of the brain that control gaze and interprets the visual input from the eye. Vision assessment is normally limited to the ‘camera’ functions of the eye. This is mainly because there are no straightforward ways of assessing visual perceptual skills and they are also highly situation dependent. The same applies to the practical testing of visual function. This is based on the use of high contrast test type (Snellen etc.) that is viewed by the foveal area of the eye in good lighting conditions and on the use of colour testing that looks again at foveal vision and its ability to correctly discriminate colour patterns or lights.
Tests of peripheral vision either to look for visual field defects, beyond the poorly validated Donders confrontation test, or to look at directed visual responses to items in the peripheral fields are not used unless a suspect problem is detected. Similarly tests for vision under low contrast conditions, tests of dark adaptation or tests of glare and recovery from it are not routinely used. In all these cases it is the lack of simple, well validated tests that means that it is impracticable, but in addition there are no well-established data on the levels of performance that are needed to be a safe and effective seafarer.
The validity of the tests that are used has roots that are distant in history. The original criteria for Snellen-based criteria were derived from studies in the 1920s on the recognition of distant channel buoys. The colour vision tests had their origins in lanterns designed to simulate navigation lights seen at night over long distances, but it was then found that Ishihara type test cards were a simpler alternative that correlated well with lantern tests and could be backed up by them when there was any doubt.
In essence standards are arbitrary and limited in terms of their evaluation of relevant facets of visual function. Most administrations have quantitative standards derived from international recommendations and these provide a consistent basis for decision taking.
Unlike most other medical conditions the emphasis in the assessment of vision has been compliance with quantitative standards. The presence of two functioning eyes has been considered important, although it is difficult to identify any major incremental benefits from this under maritime conditions given the importance of distant rather than near stereoscopic sight. The second eye can be seen as a useful insurance against either short or long term incapacitation and it is common to insist of binocularity at the start of career but to allow continuing work at sea in the event of later loss of vision in one eye.
Most eye diseases are only slowly progressive and the some of the commoner forms only become frequent and disabling after retirement age. A few relatively rare conditions arising at a younger age can be important. Retinitis pigmentosa with its associated defects in night vision and visual fields is likely to make a career in seafaring impossible, while keratoconus can be expected to lead to an impairing decline in acuity ? over a decade.
Newer treatments and prostheses have to be taken into account when assessing vision. The adoption of continuously worn contact lenses can mean that even in an emergency the wearer will be able to function with the benefit of visual correction. Corneal refractive surgery can correct vision effectively but sometimes at the cost of loss of low light acuity and increased susceptibility to glare. The examiner also needs to be aware of the tinted contact lenses that can enhance colour vision test results without improving practical colour discrimination and the use of large hard contact lenses to splint the cornea and alter its curvature, giving transient improvements in acuity.
Adequate hearing is essential for communications while at sea. In addition prolonged exposure to the noise levels often found in engine spaces can lead to noise induced hearing loss. Hearing loss, if severe, will prevent comprehension of speech and even when less severe can impair radio or telephone conversations or introduce errors into them.
The normal way of testing hearing is by pure tone audiometry. This provides information on hearing loss at a stage well before communications are impaired and is the definitive way to assess noise induced hearing loss with its characteristic pattern of a dip at 4 KHz. Loss of more than 30dB averaged over the frequencies below 2 kHz is likely to indicate a probability of communication difficulties but it does not correlate very closely with speech recognition. There are a number of tests that specifically assess speech recognition and some of these are quicker and simpler to use than audiometry as well as providing evidence to the person tested about their limitations (18). The use of simple clinical assessments such as the whisper test is subjective but can be a first step in finding out if there is serious impairment in speech recognition.
The use of hearing aids has usually been a bar to employment at sea. Their technology and reliability have improved markedly and there are now small disposable digital aids that can be worn within the ear canal for their lifetime. Such aids have the potential to enable continued employment, provided spares are carried in case of failure. For other forms of hearing aid one of the key considerations if they are removed for sleep will be whether the seafarer is still able to be aroused by emergency alarms. If not they may need to be restricted to work on vessels that return to port each night.