Human Factors

The marine community has previously approached maritime safety in terms of technical solutions in ship and equipment design. Analyses of maritime casualties, however, indicate that human factors contributed to more than 80% of maritime casualties, and this prompted a shift from technical solutions and equipment design to an approach that recognises and addresses the role of human factors in maritime safety.

Failures of human actions are often viewed solely in terms of competence rather than incomplete psychological and physiological terms. The human factor is best understood in terms of human performance within the operating system, and a simple model of human performance looks at three elements, alertness or arousal, attentiveness, and competence. Alertness is affected by:

Competence is achieved after suitable education, training, and experience, and is enhanced by the ability of an individual to acquire skills to perform the necessary tasks. Persons who hold certificates of competency for services at sea are also required to have valid medical certificates attesting that they meet prescribed standards of fitness. Aptitude is the ability or fitness of a person to acquire a particular skill related to performing shipboard tasks and ability is the capacity or mental power to be able to perform such tasks.

Ship Routine and Organisation

Ships have traditionally been organised into watch systems based on at-sea routines. The most common system is the routine on 4 hours on watch and 8 hours off watch. In the case of officers, some work is often carried on in one of the eight-hour “off” periods. In the case of ratings, their agreement or overtime payment may also involve work in a period when they are not on watch.

In smaller ships with reduced crews, six hours on watch duty followed by six hours off is common. On some ships, particularly within the offshore sector, a watch system based on 12 hours on watch and 12 hours off watch is used.

In short sea trades, particularly ferry services, a variety of shift work patterns prevail. These can involve 12 hours on duty on the ship followed by 24 hours off duty at home, or 24 hours on duty on the ship followed by 48 hours off duty at home. In the former, the personnel is involved in continuous working; in the latter, work is more or less continuous with perhaps an hour or two not actually on duty. There may well be other shift systems that could be more demanding.

The safety of a ship and crew depends on the alertness and efficiency of persons on duty who usually work watches. Living at a place of work for long periods increases the risk of human error, and the efficiency of watchkeepers can be affected by mental fatigue and reduced alertness.

Mental fatigue is likely to increase in proportion to monotony as well as stress. Reduced alertness can be experienced during watches at night, particularly late at night and early in the morning.

Yerkes Dodson Model

Experimental psychologists working in 1908 showed the relationship between arousal (or performance) as measured against stress. This showed that performance could suffer from too little stress, where boredom sets in. Also, too much stress leads to poor performance and often an overload situation, with an overwhelming number of communications and tasks.

Fatigue

Sleep is a basic human need and lack of sleep causes fatigue. Fatigue may be defined as a reduction in physical and/or mental capability as a result of physical, mental, or emotional exertion which may impair nearly all physical abilities. People on shift work might not adjust well to the routine and suffer acute or chronic fatigue.

Acute Fatigue

Acute refers to the sudden onset of a complaint, and chronic refers to a complaint that is lingering or lasting. Acute fatigue can occur in a matter of hours and is usually the result of excessive mental or physical activity. It can usually be relieved by a period of rest or sleep.

Chronic Fatigue

Chronic fatigue occurs when normal periods of sleep are insufficient to restore an individual’s working performance to its usual level. It is insidious and usually happens over some time. Chronically fatigued persons perform below their personal best.

Shift workers who do not adjust to shifting work might suffer acute or chronic insomnia. Maladjustment to shift work could cause acute insomnia within a month, with increased errors or accidents at work.

Chronic effects might be felt after five years, and could include sleep disorders, disciplinary problems, absenteeism, and diseases. An understanding of fatigue may be helped by an understanding of circadian rhythm.

Circadian Rhythm

Our lives and bodies are governed by a variety of biological rhythms. The most obvious are our heartbeat, respiration, and digestion. The circadian rhythm, which is manifested by fluctuations in body temperature, is the natural activity program of the body. The name circadian rhythm comes from the Latin words circa (about) and die (day). It is a cycle of natural alertness over a day or 24 hours (actually nearer 25 hours).

The circadian rhythm accounts for the time we are most active and the natural inclination to sleep. When the body temperature drops in this natural cycle the body’s natural inclination is to slow down, close down, and sleep. Thus between 22:00 to about 06:00, it is natural to sleep.

There is also a brief period after midday when the body activities drop, the after-lunch nap or siesta period. The circadian rhythm is not adaptive to any different daily routine. Shift workers, whether watchkeepers at sea, airline pilots, or factory workers all experience temperature drops as illustrated above, no matter how long the person has been on a particular shift.

This also has important implications for rapid longitudinal or meridional travel – “jet lag”. Staff joining ships by plane and having travelled long distances east and west will take days to readjust to the light (daytime) and dark (night). The rate of adjustment is about one day per hour different from the origin.

Circadian Rhythm Disruption Manifests Itself In:

Fatigue and Casualties

Proving that, at the balance of probabilities, fatigue is a causal factor in a marine casualty can be difficult. Some attempts have been made to establish an index to indicate the probable presence of fatigue as a factor in an accident.

The Sleep Credit/Deficit System

This is a simple system of assessing an individual’s hours of sleep and wakefulness over the preceding days, preferably at least 72 hours (longer if possible). Over the days that data is available, credit two points for every hour asleep and debit one point for every hour awake. The chart to the right shows only a 50-hour analysis. This system does not account for physical or mental exertion and is an index of possible fatigue factors. The information can be captured on a proforma.

Fatigue Index Score

The Fatigue Index Score (FIS) has been devised by consultants to the US Coast Guard. The FIS is a formula that is based on mathematical analysis of accident and incident data, already contained in the Coast Guard database. The application of this formula is a value known as the “Fatigue Index Score”.

The purpose of this calculation is to give investigating officers a general tool by which to evaluate the presence of fatigue observed in persons associated with the incident. It is not (yet) considered an appropriate tool to estimate the magnitude of fatigue present, however, though someday this may be possible. The application of this formula has been tested and found reliable in correctly identifying fatigue as causal to the incident in about 80 per cent of the trials.

While this is not 100 per cent, and perhaps no measure of personal fatigue will ever be so, a tool that may be used to confirm or rule out the causal relationship of fatigue or other factors to the 80 per cent mark, is no less significant. Symptoms of fatigue are forgetfulness, difficulty operating equipment, being less motivated, and being distracted.  One can also have difficulties keeping eyes open, sore muscles, and a desire to sit or lie down. 

A simplified version of the Fatigue Index Score formula is as follows:

FIS = (WH x 6.1) – (SH x 4.5) + (S x 21.4).

• WH = The number of hours WORKED in the 24 hours before the casualty.
• SH = The number of hours SLEPT in the 24 hours before the casualty.
• S = The number of SYMPTOMS experienced by the individual while on duty before the casualty.

For example, a person who has worked 8 hours in the previous 24, slept 6 hours in the 24, and reported one of the seven symptoms would score:

FIS = (8 hrs work x 6.1) – (6 hrs sleep x 4.5) + (1 symptom x 21.4) = 43.2

Understanding the results of the FIS is however a bit more complex. If the FIS is > 50 there is an 80 per cent likelihood that fatigue was a cause of the incident. For a score < 50, there is similarly an 80 per cent likelihood that fatigue was not a cause.

While the FIS formula is useful, there are certain factors not considered. Such as the timing of work or sleep as compared to the body’s circadian cycle, quality of sleep, and other environmental factors such as heat and cold. The formula has a predictive value, particularly in highlighting areas of work-rest patterns.

Factors Affecting Alertness

Research has shown that nine internal or external factors and stimuli are relevant to the level of alertness in an individual. They are called “The nine switches of alertness" and are:

Time of Day

People working regular shift work where the periods of work are not changed can adapt to the different sleeping periods without too much ill effect, their biological clock adjusting to the changed conditions. Thus mariners can adjust their watch regime, the time of day switch being in the “on” position at the required times.

Sleep Bank Balance

As a general and approximate rule, sleep deprivation occurs and the alertness switch goes to the “off” position when an individual exceeds the total “sleep credits”. Sleep credits are considered to accumulate at a rate of two for every hour's sleep and to expand at the rate of one for every hour awake. Hence, after eight hours of sleep, an individual can be considered to have 16 credits, which are expended over the next sixteen hours.

Ingested Nutrients and Chemicals

After a watch, the ingestion of too many stimulants may prevent a person from sleeping although physically tired. Similarly, while alcohol and depressants can get people to sleep, they interfere with the sleep quality and a person may awake tired and unrefreshed.

Factors Affecting the Degree of Performance

The factors generally considered to affect the degree of human performance are those which include amongst others:

• Workload.
• Personality.
• Motivation.
• Experience.
• Tiredness.
• Health.
• Change.
• Technology.
• External factors (environmental and personal).

Unsafe acts or active failures are types of actions, by individuals, that are normally involved in breaching defences against accidents. Unsafe acts can be errors or violations, where errors are accidental failures or acts, or violations are deliberate failures or acts.  Violations can be routine, taking shortcuts, optimising for other reasons than safety, and exceptional one-off breaches of the rule. Errors can be broken down into:

• Slips or failures of attention resulting from intrusions or omissions.
• Lapses of memory failures such as omitting items that should be covered.
• Mistakes which can be rule-based (by applying a bad rule), or knowledge-based (a new situation for which training has not provided a rule-based solution).

Accidents and incidents require investigation to determine causes in terms of human factors. Analysis of causes overcome time might reveal similar patterns related to certain aspects of human performance. Safety recommendations could then be drawn up to prevent similar accidents in the future.

A study in 2020 looking into factors that effect performance in the workplace was completed. If you would like to read more on this topic please view the attached findings of the study (this was a shore based study).