Establishing a fatigue risk profile

Tuesday, November 18, 2014 by Chris Hocking

The most common health problem reported by an estimated 75% of shift workers is disturbed sleep. It only takes one week of poor quality or restricted sleep to induce performance impairment equivalent to having a blood alcohol concentration of 0.1, significantly increasing the risk of an accident. It is not surprising then; up to 30% of serious accidents are directly related to fatigue. The performance impairments attributable to fatigue not only make people less effective, but also very unsafe. Numerous studies have found a relationship between fatigue and work-related injuries. Excessively sleepy or fatigued workers are 70% more likely to be involved in industrial accidents than alert, well-rested individuals.

Conventional strategies to mitigate the effects of fatigue in shift-working occupational settings, particularly in the transport and mining industries, are primarily centred on regulatory and organisational approaches. These include limits to hours of duty, education, and training. Such approaches are essential and have positive effects on workplace alertness, safety, and productivity. However, there are numerous limitations to the effectiveness of these approaches, as fatigue is a common and unavoidable by-product of shift work. People don't adapt to shift work, particularly evening work, night work and rotating shift schedules. Without the ability to objectively measure fatigue, it is almost impossible to effectively manage the associated risks
.

Using technology to reduce fatigue-related risk

The use of objective data to quantify fatigue levels of specific groups of drivers/operators allows companies to mitigate their exposure to fatigue-related risk by tailoring working time arrangements to suit particular operational settings. Technology can provide companies with the necessary objective information to evaluate all aspects of their shift roster design by identifying areas of risk specific to the operational environment. Objective information then forms the basis upon which to make informed decisions tailored to the unique operational needs of the site.

Optalert's products use the only safety system in the world continuously providing real-time objective, scientifically-validated alertness information to both drivers (in cab) and supervisors (through Optalert's Individual Risk Indicator System (IRIS™). The continuous flow of information offers multiple layers of protection against the dangers of fatigue and allows all parties to monitor the associated risk and initiate proactive measures before it reaches dangerous levels.


The fatigue-risk profiles from 24-hour operations typically resemble the circadian rhythm of alertness. This is characterised by increased risk during night shift, particularly during the early hours of the morning. This time of day also aligns with the low-point in the circadian rhythm of core body temperature when the body is most in need of sleep. These circadian patterns are consistent with the known relative risk of truck fatalities for each hour of the day illustrated below.


Figure 1.
Relative risk of fatal truck accidents by time of day. The yellow line represents the circadian variation of core body temperature. Source: Viewpoint - Perspectives on Modern Mining, 2007, Issue 2, pg 29. Caterpillar Global Mining

The cumulative effects of fatigue
To illustrate how Optalert’s Fatigue Risk Profiler (FRP) data is being used by mine sites to develop a profile, consider the following graphs depicting alertness levels and frequency of fatigue warnings from 238 mine haulage vehicle operators working on a roster of 12-hour day and night shifts over several months. This involved more than 103,000 hours of objective data (Figure 2).


Figure 2. Average alertness levels (Left graph) recorded from 238 drivers during day shifts and night shifts (blue shaded region) for a total of 6.2 million fatigue scores. The frequency of in-cab Optalert warnings (medium and high risk) per hour of driving (right graph) issued to the same drivers.

The fatigue risk profile for this fleet of mine haulage drivers indicates the lowest levels of risk are observed at the beginning of day shift and night shift (7am, 7pm) with peak risk observed during the early hours of the morning (3am – 5am). While specific areas of risk are highly influenced by shift roster design, the overall patterns of these profiles often follow a strong circadian variation of alertness throughout the day. Keep in mind however, a company’s shift roster design can influence the times of the day when fatigue-related risk is greatest.

Evaluating shift roster design

With the generated fatigue risk profile, the data can be further analysed to evaluate all aspects of a company’s shift roster to identify areas of risk within the system specific to the operational environment and shift design in use. These can include evaluations of; shift duration, start and end times, scheduling of breaks, roster cycles, and scheduling over time.

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