Chapter 5: Level 1 Controls: Providing Sufficient Sleep Opportunity

Learning Outcomes

On completing this chapter, you will be able to:

  • Describe the characteristics of a schedule that would increase the likelihood of work-related fatigue.

  • Assess the scheduling practices of your organization with respect to mental fatigue.

Level 1 Controls: Providing Sufficient Sleep Opportunity

Hazard-Control Model for Fatigue Risk Management
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Hazard-Control Model for Fatigue Risk Management

In the past, fatigue has been largely managed through scheduling regimes, usually through rules governing hours of work imposed by regulators, organizations, or union bodies. In a fatigue-risk management system, however, there are five major levels of control: organizational, individual, behavioural, error, and incident level. A successful fatigue risk management system addresses each of these levels by organizing defence systems around these layers. This chapter addresses Level 1 of the hazard control model.

Level 1 controls are aimed at ensuring that the work schedule provides employees with sufficient sleep opportunity. To achieve this, the following factors should be considered:

  • length and timing of shifts

  • length and timing of breaks

  • number of shifts worked in a row

  • number of days off between shifts

Using factors such as these, an organization can predict, on average, how much sleep an employee will obtain. This chapter provides an overview of some strategies for assessing work schedules and their impact on sleep, alertness, and fatigue.

Assessing Schedules for Adequate Sleep Opportunity

The major reason for assessing work schedules, apart from ensuring that they comply with industry requirements and other rules, is to understand the likely impact that specific hours of work have on sleep opportunity. Sleep is the only cure for fatigue. In the context of an FRMS, the employer has the responsibility to ensure that adequate opportunity is provided for sleep between work shifts. It is the employee's responsibility to use the opportunities given to obtain recovery sleep.

Most people need between seven and nine hours sleep to maintain safe performance and alertness levels. Depending on the time of day that a break is provided, the amount of time off needed to get adequate sleep could be as little as 10 hours and as much as 20 or more. This reflects the fact that employees do not simply fall asleep as soon as they leave work and wake just before they return. People have many activities and responsibilities to manage between shifts such as commuting to and from work, eating, showering, socializing, relaxing, spending time with family and friends, etc. To ensure adequate rest, sleep opportunity needs to include time for employees for recovery sleep and other activities.

Work schedules may be assessed by examining specific aspects of the hours of work. The questions provided below can be used as a guide, but they should not be seen as a complete list for all circumstances. Sleep opportunity alone should not determine appropriate schedules, even though it is generally the most important factor. For example, early morning start times generally produce higher levels of fatigue, but a 5 a.m. start may be more appropriate than working under extremely hot and humid conditions in the afternoon. This reflects the risk-based approach of safety management systems (as discussed in Chapter 3).

The following are some questions that could be asked to assess sleep opportunity and potential fatigue:

  1. How many hours are worked per seven-day period? Not surprisingly, as total hours worked increase, sleep opportunity decreases.

  2. What is the maximum shift length? As the length of a given shift increases, the subsequent sleep opportunity decreases.

  3. What is the minimum length of time off between shifts? A short break is defined as a single sleep opportunity between subsequent work periods. It is typically a period of less than 32 hours. Not surprisingly, as the break between subsequent shifts decreases so does the sleep opportunity.

  4. How many hours are worked between 9 p.m. and 9 a.m.? This question considers late finishes, early starts and night work. All of these will reduce night sleep opportunity and result in a significant reduction in total sleep opportunity.

  5. How often do employees get a long break from work? A long break is defined as a period of two night sleeps with a non-working day in between. Long breaks typically provide a significant opportunity to recover from sleep loss accumulated over a series of shifts.

The table below provides an example of how questions like those above can be quantified into a rule system.

Fatigue Likelihood Scoring Matrix for Work Schedules
Score 0 1 2 4 8
a) Total hours per 7 days < 36 hours 36.1 – 43.9 44 – 47.9 48 – 54.9 55+
b) Maximum shift duration < 8 hours 8.1 – 9.9 10 – 11.9 12 – 13.9 14+
c) Minimum short break duration > 16 hours 15.9 – 13 12.9 – 10 9.9 – 8 < 8
d) Maximum night work per 7 days 0 hours 0.1 – 8 8.1 – 16 16.1 – 24 > 24
e) Long break frequency > 1 in
7 days
< 1 in
7 days
< 1 in
14 days
<1 in
21 days
< 1 in
28 days

In the table above, a 9 a.m. to 5 p.m. work week (5 days in a row) would produce a score of zero. On the other hand, a work schedule of seven 12-hour night shifts, followed by seven days off would produce a score of 21, which would be considered high. The figure below shows examples of schedules scored using this approach.

Fatigue Likelihood Score | Examples of different schedules scored using the Fatigue Likelihood Scoring Matrix
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Examples of different schedules scored using the Fatigue Likelihood Scoring Matrix

Calculating a score for a schedule allows companies to quantify what they deem to be acceptable or unacceptable. The cutoff score for an acceptable schedule will be determined by the specific characteristics of the organization. For example, an organization could choose to assign a lower cutoff score for highly complex or safety-critical work, or for a high-stress work environment (e.g., high humidity) than for less critical work in an air conditioned environment. In the beginning, cutoff scores will be best estimates. However, as an organization's understanding of its own fatigue hazard improves through collecting data on actual sleep (see Chapter 7) and fatigue-related errors, it should reassess scores that show signs of providing insufficient sleep opportunity.

Fatigue Modelling

Although fatigue cannot be measured like alcohol or drug impairment, there are ways it can be assessed. Work schedules can be used to predict fatigue based on the likely sleep loss caused by a specific shift pattern. Predictive software models can provide fatigue likelihood scores on the basis of a schedule.

Many models predict fatigue based on planned or actual hours of work. In doing so, they consider a number of factors known to be relevant for work-related fatigue. These factors include the timing and duration of all previous work shifts (with more weight given to the most recent shifts). Most models also allow comparison of the fatigue scores that various schedules may impose on an employee population. In addition, organizations can set different threshold values for fatigue likelihood scores, based on a risk assessment of tasks within their operation. In other words, a score may be designated acceptable for low-risk tasks, but unacceptable for tasks that involve a much higher potential safety risk. One limitation of such a system, however, is that it does not tailor predictions for every single employee.

As with any fatigue management tool, testing devices and models should form part of an integrated system, not replace it. Each organization should understand the likely impact of fatigue in the context of the work tasks that its employees perform.

Designing the Ideal Shift System

It is important to understand that there is no such thing as a “perfect” work schedule. There are always a multitude of factors to consider. For example, while managing fatigue and providing sufficient sleep opportunity is important, it is also important to ensure employees receive sufficient family and social time away from work. The ideal schedule would be from 9 a.m. to 5 p.m. However, in today's world of 24-hour demand and supply, companies often require employees to work outside these hours.

A fatigue-friendly schedule would ensure that all shifts are finished between nine and ten o’clock at night so employees could go home and easily get eight hours of sleep without having to wake up too early. However, such a schedule leaves little time for socializing or spending time with family, and could lead to feelings of social isolation and depression.

A social-friendly schedule, on the other hand, would have employees starting work in the early hours of the morning and finishing mid-afternoon to enable them to spend time with family and friends. However, since it is unlikely that an employee would go to bed before ten or eleven o'clock at night, this type of schedule significantly limits the opportunity for sleep before the next shift.

The ideal shift for one employee is not likely to satisfy all employees. For example, a schedule that suits an employee with two young children would be unlikely to suit another employee who likes to sleep in and stay up late. While sleep should be the primary concern, other factors (such as family and social life) should also be considered when designing new shift systems.

Considerations to Maximize Sleep Opportunity in Designing Work Schedules

As discussed in Chapter 1, prescriptive rules based solely on schedule design may be appropriate for ensuring recovery from physical exhaustion. However, they are of limited benefit in managing mental fatigue. More effective strategies for reducing physical and metal fatigue focus instead on the time available for sleep (or sleep opportunity) and actual sleep obtained (see next chapter).

Things to consider in designing work schedules include, but are not restricted to:

  • limiting night shifts

  • reducing shift length to 12 hours or less

  • limiting early morning starts

  • limiting extended duty hours/overtime

  • recording and controlling overtime

  • ensuring appropriate breaks during shifts (coffee, meals, etc.)

  • providing sufficient time off between shifts to allow for minimum sleep requirements

  • limiting long blocks of work (i.e., multiple days worked one after the other)

  • planning as much of the actual hours of work as possible

  • creating a napping policy and facilities, including a process for managing sleep inertia

- List some of the main characteristics of a work schedule that increases the likelihood of obtaining sufficient sleep between shifts.
- What score would your typical work schedule produce on the Fatigue Likelihood Scoring Matrix?
- Explain why you might choose a computer-based modelling tool over prescriptive hours-of-work rules.

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