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WORKPLACE FATIGUE AND DROWSINESS ROWSY DRIVING IS NOT SIMPLY A MATTER OF FATIGUE: CLARIFYING THE NATURE OF A PROBLEM AT MINE SITES Experimental evidence indicates that drowsiness and fatigue are not the same, writes Dr. Murray Johns. It has been estimated that 93 per cent of accidents and incidents involving haul trucks at mine sites are caused by human error. Of those, 60 to 70 per cent have been attributed to drivers being drowsy or fatigued at the time.1 Even minor crashes can be very costly, not only in terms of human health and safety, but also the continuity and cost of production. for heavy-vehicle drivers, the National Transport Commission assumed that fatigue included ‘feelings of drowsiness’3 , i.e. they assumed that drowsiness is part of fatigue. Alternatively, some prominent researchers have suggested that fatigue is a state resulting specifi cally from sleep deprivation, poor quality sleep, or sleep at times of circadian rhythm dysregulation.4 Others say that fatigue is simply the state of reduced ‘alertness’, whatever its cause. Others again imply that fatigue is that which causes impairment of performance over time, which seems to involve a circular argument. There has been very little discussion about these different defi nitions. This is not unique to Australia.5 unique to the mining industry. Nor is it Figure 1. A relatively minor crash in a haul truck can be very expensive in terms of repairs and loss of production, even if there is no personal injury. What is interesting in this and many other related reports is that drowsiness and fatigue are neither defi ned nor distinguished. Does this mean that there are two different states, drowsiness and fatigue, each of which is associated with increased crash risk for drivers? Alternatively, does it mean that the two words refer to the same thing? Or are we just confused about the nature of this problem and don’t know which word to use? If so, does it matter? Our aim here is to answer those questions. Background About a century ago, applied psychologists began to study fatigue as a cause of impaired performance in the workplace, mainly as a function of the “hours of work”. The idea that fatigue was a major cause of road traffi c accidents arose later, but nonetheless has a history going back several decades.2 Throughout those years there has been diffi culty in reaching a consensus about what fatigue is. When developing Australian guidelines and regulations After reviewing the published literature and having personal discussions with many researchers around the world, it appears to the present author that most of them assume they know what fatigue is and how it relates to impaired performance. However, they often seem to be talking about different things without recognising that other people do not share their ideas and assumptions, couched almost exclusively in terms of fatigue. Some have expressed the opinion that if we used an alternative word such as drowsiness, which may be more accurate and appropriate in relation to road safety, the general public would be unnecessarily confused. A cynic might conclude that the word fatigue belongs to the world of Alice in Wonderland, where words mean what we want them to mean. Does this matter? It would seem sensible to want to understand the nature of this problem and how to measure it if we are to manage its risks. Of course, such discussions have far wider implications than for the mining industry alone, including all industries in which impaired human performance can be of critical importance. This report highlights the confused state of thinking about this problem, especially as it relates to the risks of drowsy driving at mine sites. We shall try to clarify the nature of the problem by examining the different defi nitions of the terms used and the conceptual framework from which they emerged, and placing a new emphasis on the state of drowsiness rather than fatigue. Finally, a new method for detecting and measuring drowsiness in drivers is described briefl y. This is already helping to address the problem of drowsy driving at mine sites. Defi nitions of fatigue, tiredness, drowsiness and sleepiness A good starting point for us to clarify the nature of this problem is to consult English dictionaries, rather than individual researchers, about commonly accepted defi nitions of the relevant words. According to the Oxford English Dictionary (OED), the noun fatigue means “‘weariness resulting from bodily or mental exertion’. The adjective, tired, is a synonym for being ‘fatigued or weary’”. Another dictionary defi nes fatigue in one sense as, “temporary loss of strength and energy from hard physical or mental work, and in another sense (when used in conjunction with a modifi er) as ‘boredom resulting from overexposure to something,’” e.g. battle fatigue, in which there is reduced responsiveness to a stimulus or situation as a result of repeated or prolonged exposure. By contrast, the long-established meaning of the word drowsiness is quite different. The OED defi nes the adjective drowsy as, “inclined to sleep, heavy with sleepiness, half asleep.” Thus, drowsiness is the intermediate state between alert wakefulness and sleep. There is no ambiguity in the difference between the common English meanings of these words – fatigue (of which tiredness is a synonym) refers to a quite different state from that of drowsiness (of which sleepiness is a synonym). Consistent with the common usage of these words, people who run marathons say they feel fatigue as the race progresses and for some time afterwards. Yet there is no evidence that they are drowsy or fall asleep soon after they cross the fi nishing line. As we shall see, one can be very fatigued (in this case with muscular fatigue) without being drowsy. At other times, we may be drowsy without being fatigued and, at other times again, both fatigued and drowsy at the same time. AUSTRALASIAN MINE SAFETY JOURNAL 11