The Fatigue Management Program for Airport Workers in New Zealand. An Evaluation

Table of contents

1. Executive summary

2. Purpose and objectives

3. Evaluation process

4. Conclusions and results
4.1 Learning
4.2 Behavior modification
4.3 Transfer
4.4 Reaction to the training experience
4.5 Conclusion

5. Recommendations

References

1. Executive summary

Airports, like hospitals, never close and, as such, healthcare providers and aviation professionals operate under a distinctive but shared set of circumstances (Feiner, 2017).

As a result, long and intensive shifts are common, sleep deprivation and fatigue are widespread.

Therefore, fatigue can be defined as the decreased capability to perform mental or physical work, produced as a function of inadequate sleep, circadian disruption, or time on task (Brown, 1994 as cited in Safety Institute of Australia, 2012).

Circadian disruption refers to wake and sleep that occur outside of the body's circadian rhythm. Circadian rhythms regulate different functions of the body to an average 24.2-hour cycle (Czeisler et al., 1999 as cited in Safety Institute of Australia, 2012). These rhythms are evident in functions such as sleep propensity (the ability to initiate and maintain sleep), body temperature, performance and mood (S. S. Campbell & Murphy, 2007; Clark, Watson, & Leeka, 1989; Kryger, Roth, & Carskadon, 1994; Lack & Lushington, 2003 as cited in Safety Institute of Australia, 2012).

In "figure 1", the circadian rhythm of sleep propensity is shown and demonstrates how the homeostatic drive for sleep and the circadian system interact to regulate the sleep/wake cycle.

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Figure 1: Borbély's model of sleep-wake regulation. Process S represents the homeostatic built-up of sleep pressure. Process C represents the circadian rhythm. When the distance between process S and process C is largest, sleep propensity will be highest (Borbély & Achermann, 1999 as cited in Moens, 2010).

The circadian rhythm has peaks and troughs. The circadian nadir - the low point of the circadian rhythm which typically occurs in the early hours of the morning also called the window of circadian low (WOCL).

During this time, core body temperature is at its lowest and sleep propensity is at its highest (Dijk & Czeisler, 1995 as cited in Safety Institute of Australia, 2012). Sleep during the circadian nadir is associated with greater restorative value and feelings of rest upon waking (Äkerstedt, Hume, Minors, & Waterhouse, 1997 as cited in Safety Institute of Australia, 2012).

If wake occurs during this time, the individual is likely to experience a depressed mood and is unlikely to perform at an optimum level (Äkerstedt, 2003; Frey, Badia, & Wright, 2004; T. H. Monk et al., 1997 as cited in Safety Institute of Australia, 2012).

In the hours following the circadian nadir, there is an increase in core body temperature and a decrease in sleep propensity, leading to waking. The peak of the circadian rhythm is when core body temperature is highest and sleep propensity is lowest, and typically occurs at approximately 17:00. This time of day is associated with high levels of function and alertness. Sleep occurring during the peak is likely to be restless and truncated (Äkerstedt, 2003 as cited in Safety Institute of Australia, 2012).

In summary, wake that occurs out of synchrony with the circadian drive for wakefulness is characterised by impaired functioning, excessive sleepiness and increased fatigue.

Also, sleep that occurs out of synchrony with the circadian rhythm is likely to be of reduced restorative value. Both of these circumstances are likely to result in increased fatigue ("figure 2”).

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Figure 2: Window of circadian low (WOCL). Points daily minimum body temperature; more sleepy and least able to perform mental/physical tasks (IATA Training, 2021).

Besides, fatigue should be treated as an impairment, similar to being under the influence of alcohol or drugs as demonstrated by Dawson and Reid (1997) in "figure 3”.

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Figure 3: Performance in the sustained wakefulness condition expressed as mean relative performance and the percentage blood alcohol concentration equivalent (Dawson & Reid, 1997).

Thus, comparing means relative performance and blood alcohol concentration equivalent against hours of wakefulness clearly indicate that the effects of moderate sleep loss on performance are similar to moderate alcohol intoxication.

For instance, after seventeen hours of sustained wakefulness cognitive psychomotor performance decreased to a level equivalent to the performance impairment observed at a blood alcohol concentration of 0.05%. This is the proscribed level of alcohol intoxication in many western industrialised countries.

However, the authors believe that the performance impairment associated with shift work could be even greater than reported in their study.

Indeed, as about fifty per cent of shift workers do not sleep on the day before the first night shift, levels of fatigue on subsequent night shifts can be even higher (Dawson & Reid, 1997).

In "figure 4", Folkard and Tucker (2003) show the correlation between incidents/accidents and morning, afternoon and night shift with the last one having the biggest increase in the risk of incidents/accidents.

Simultaneously, they indicate what is the performance efficiency at a different time of the day. As shown, it has a negative value from midnight until six in the morning (Folkard & Tucker, 2003 as cited in Gregory, 2020).

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Figure 4: Industrial performance efficiency over the twenty-four hours/day (Folkard & Tucker, 2003)

Furthermore, the authors prove that there is an increase of relative risk during the length of consecutive shifts. However, they are greater during successive night shifts ("Figure 5”).

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