Keywords

1 Sleepiness in Industry

The utilization of time as expressed in 24-h work operations, together with the widespread use of automation, will continue to escalate in the next century, further increasing the risks of sleepiness-related accidents when more workers carry out vigilance-based activities at times other than traditional daytime work hours. Decreased alertness resulting from insufficient or poor quality sleep can have several safety-related consequences, including slowed response time, reduced vigilance, reduced decision-making ability, decreased attention to detail, impaired judgment, distraction during complex tasks, and loss of awareness in critical situations. This can affect productivity, safety, and overall health.

Advances in sleep science and circadian biology indicate that adequate sleep at the correct circadian time is important not just for workplace performance and safety, but also for overall physical and mental health. Impairments in physical health, cognition, alertness, work productivity, and daily activities caused by excessive sleepiness in industrial workers are well documented [1–4]. It has been observed that impairment of productivity caused by presenteeism resulting from excessive sleepiness (>30 %) is similar to impairment of presenteeism due to other chronic conditions, such as diabetes, depression, and arthritis [5]. In a recent study of 4,188 employees at four US corporations, workers with insomnia or insufficient sleep had worse productivity, performance, and safety outcomes. Fatigue-related losses in productivity cost an estimated $1,967 per employee each year [6].

The causes of an increased propensity to sleepiness in industrial employees can be roughly divided into two categories. The first, which is common to all production activities, includes shift and night work, work-related stress, physical and mental fatigue, and the use of illegal or legal drugs and alcohol. All these causes have been discussed in previous chapters. Some industrial activities may also expose workers to specific factors that may increase drowsiness. Effective prevention of the possible negative effects of drowsiness in industries must carefully consider these intrinsic causes of sleepiness.

This chapter will briefly examine the second cause of increased daytime sleepiness in industrial activities, considering separately the organizational and physical factors and the specific neurotoxic agents that may be present in the production cycle.

2 Organizational and Physical Factors

Probably the most important cause of sleepiness is shift work. For employers, shift work represents an opportunity to increase production and customer service without major increases in infrastructure. Nevertheless, sleep disturbances and fatigue involve significant costs related to lost productivity and arouse concern regarding the safety and well-being of workers. There is extensive scientific literature on the negative impact of sleep deprivation in a number of shift-working occupational groups, and also the deleterious health effects of extended shifts and overtime. For example, extended shifts, night shifts, and overtime work have been linked to an increased risk of fatigue, sleep disturbances, impaired mood, illnesses, negative cardiovascular outcomes, injuries, and impaired work performance [7–9].

One of the most important (but frequently overlooked) root causes of employee fatigue and sleepiness is an imbalance between workload and staffing levels. Staffing levels play a dominant role in determining the amount of overtime per employee, the length of shifts and time off between shifts, as well as the discrepancy between the published shift schedule and the actual shift schedule worked. This is because, in most 24/7 operations, there is a fixed number of positions to be filled on each shift. If the staffing level is lower than optimal, then the employees in that operation have to work additional hours or extra shifts to keep the positions filled. Understaffing increases the probability of shortened sleep and extended time on duty as well as increased overtime and unpredictability of the work-rest schedule, thus affecting both the quantity and the quality of sleep.

Besides working time arrangements, other characteristics of work organization may contribute considerably to daytime sleepiness. For example, psychosocial factors, such as changes in workload, job satisfaction, and depressive symptoms were associated with daytime sleepiness in a longitudinal study of pulp and chemical workers [10]. A recent review demonstrated that stress is closely related to impaired sleep in many cross-sectional studies, especially if high demands or effort are anticipated for the following day. Sleep recordings showed that stress is associated with shortened sleep, fragmentation, and possibly a reduction in sleep stages 3 and 4. Shortened or disturbed sleep causes increases in levels of traditional stress markers (e.g., cortisol) and may thus exacerbate the effects of stress [11].

Among the environmental factors affecting sleep, importance must be given to noise. Noise is considered to be a nonspecific stressor which generally causes physiological and psychological effects in an individual. Many occupations involve workers being subjected to loud noise levels without adequate protective measures. A retrospective cohort study showed that there is a strong association between occupational exposure to loud noise and poor sleep efficiency [12].

Other environmental risk factors are heat and lighting. Symptoms of drowsiness are common in workers exposed to moderate heat stress, even if their work activity is classified as light on the basis of energy expenditure [13]. Environmental conditions such as lighting and thermal comfort are influencing factors on sleep quality [14].

3 Neurotoxicant Exposure and Drowsiness

The nervous system is the major target of the toxic effect of many substances (Table 13.1). Central nervous system manifestations of neurotoxicity vary depending on the type and conditions of exposure to neurotoxicants; these include chemical concentrations and route of exposure. The most common syndrome following an exposure to high doses of neurotoxicants is probably an encephalopathy caused by diffuse dysfunction of cortical or subcortical structures. Acute exposure may lead to drowsiness, somnolence, or loss of consciousness resulting from neurodepression. In some cases, these symptoms are preceded by euphoria and signs of neurostimulation. Other toxicants may cause relatively selective injury in the vestibular system or the cerebellum, resulting in ataxia, or in basal ganglia, leading to an extrapyramidal syndrome. Nowadays, neurological diagnostics is directed toward early detection of symptoms and abortive forms, so cases of serious damage to the nervous system are no longer reported. However, the effect of industrial pollutants may have a synergic effect on other causes of increased sleepiness and may cause significant problems in the workplace.

Table 13.1 Neurotoxic substances: sources of exposure and clinical features
Full size table

4 Indoor Air Quality

Among the intrinsic causes of increased sleep propensity in industrial workers, attention should be given first of all to the effects on vigilance and sleep function of common indoor air pollutants such as carbon dioxide (CO2), carbon monoxide (CO), and nitrogen dioxide (NO2). At low doses, these pollutants are present in all workplaces, including offices. As with other industrial pollutants, the effects of exposure to high concentrations are well known, while the dose–response relationship at low doses needs further clarification.

Long-term exposure to elevated ambient CO2 levels is a common condition of living in a closed environment. Long-term intermittent exposure to high ambient CO2 has been shown to cause respiratory disturbances during sleep in submariners [15]. An experiment showed that sleep quantity and quality were reduced in volunteers living in a closed system under elevated ambient CO2 levels of 0.7 and 1.2 % [16]. Although we currently lack confirmation from field studies, poor air quality may induce neurobehavioral effects in all workers living in a closed environment, altering their ability to concentrate and increasing drowsiness.

Miners, tunnel workers, and subjects working in enclosed spaces where combustion occurs are exposed to significant concentrations of carbon monoxide. Inhaling low concentrations of carbon monoxide in the range of 0.01–0.02 % may cause headache and mild confusion. A higher concentration of 0.1–0.2 % often results in somnolence and stupor, and inhalation of more than 1 % for 30 min is usually fatal. The effects of long-term exposure to extremely low levels of carbon monoxide are unclear. A wide range of nonspecific symptoms, including drowsiness, have been attributed to low-dose exposure to CO, but the cause-effect has not been proved. Occupational exposure to low concentrations of carbon monoxide may possibly influence the synchronization of upper airway and lower respiratory muscles and thus induce sleep disordered breathing, but on-field studies have failed to demonstrate this hypothesis [17].

Mining operations conducted at high altitudes provide health challenges for workers, because exposure to carbon monoxide may be enhanced by low levels of oxygen. Hypoxia experimentally causes severe disruption of both rapid-eye-movement (REM) and non-REM sleep. Acute exposure of rats to 10.5 % O2 (corresponding to 5,030 m altitude) during daylight hours virtually abolished REM sleep and shifted the distribution of amplitudes of slow-wave sleep EEG toward awake values. Similar disruption of sleep occurred during inhalation of 0.05 % CO with steady-state carboxyhemoglobin of approximately 35 % [18]. A review of the literature shows that poor sleep quality and sleep-disordered breathing may contribute to daytime sleepiness and impaired cognitive performance that could potentially result in workplace injuries, particularly in miners who are already at increased risk of unintentional workplace injuries [19].

5 Specific Neurotoxic Substances

Many raw materials or chemicals used for industrial production may cause drowsiness. Among these, solvents constitute a very heterogeneous category. Because most organic solvents contain mixtures of ingredients, it is often difficult to attribute specific changes to a particular substance. Most organic solvents possess acute narcotizing properties. Brief exposure at high concentrations causes a reversible encephalopathy. Chronic exposure to moderate or high levels of solvent may cause a dementing syndrome, with mood and personality changes, and memory and sleep disturbances. A sensorimotor polyneuropathy may also be present. Some examples of solvents are given in Table 13.1.

Workers chronically exposed to mixtures of organic solvent (containing xylenes, ethyltoluenes, trimethylbenzenes, propylbenzene, ethylbenzene, toluene, aliphatic hydrocarbons, and the components of painter’s naphtha) in the manufacture of paints and lacquers, at concentrations within or slightly exceeding MAC values, reported sleep disorders, and sleepiness during the day [20]. Long-term exposure to solvents impaired vigilance in serigraphy workers [21]. There is therefore the possibility that industrial workers exposed to environmental solvent concentrations defined as “acceptable” by law, may experience increased sleepiness of a toxic nature.

Many other organic substances have a toxic effect on the central nervous system, possibly increasing drowsiness at low doses. Monohalomethanes, such as methyl iodide (CH3I) [22], methyl chloride (CH3Cl) [23], and methyl bromide (CH3Br) [24] are neurotoxic and can induce both acute intoxication with delayed neuropsychiatric sequelae and chronic neurotoxicity.

Acute exposure to organophosphate and carbamates causes drowsiness. The long-term sequelae of exposure to low doses of organophosphate compounds are ill defined, with various effects reported on a range of indices of central nervous system functions such as sleep, cognitive performance and electro-encephalogram. Above and beyond what has been observed in experimental studies [25], the real effect on humans still needs to be fully investigated.

Some metals, such as lead, exert a significant neurotoxic effect. Acute high-level lead exposure typically results in a syndrome of abdominal colic accompanied by neurologic symptoms, including lethargy. Effects of low-level lead and arsenic exposure on copper smelter workers have been shown to include sleep disturbances and other neurotoxic symptoms [26]. It is known and widely accepted that increased lead absorption is associated with “nonspecific” subjective symptoms, such as sleep disturbance [27].

Mercury intoxication can be induced by either organic or inorganic mercury. Like many other toxins, mercury poisoning causes a nonfocal encephalopathy. Laboratory studies showed that lead poisoning induces reversible changes in sleep-waking patterns [28]. Chronic exposure to organic mercury in humans can produce tremor, dysarthria, ataxia, and mental disturbances. Workers exposed to inorganic mercury fumes reported more sleep disturbances than controls [29].

Of the neurotoxic metals, manganese is especially well-known for its acute behavioral manifestations. Acute overexposure causes an initial phase of agitation, termed “manganese madness,” and heralds chronic poisoning. Ship and electrical industry workers chronically exposed to manganese within the range of <0.01–2.67 mg/m3 showed subclinical effects on the nervous system, consisting in increased emotional irritability, dysmnesia, concentration difficulties, sleepiness, and limb paresthesia [30]. Bridge welders working in a confined space with a mean time weighted average of Mn-air ranging from 0.11 to 0.46 mg/m3 manifested high prevalence of sleep disturbance (79.1 %) [31].

6 Conclusions

Nowadays, there is an increasing awareness that hours-of-service guidelines alone may fail to achieve their objective of maximizing alertness (and thus fitness for duty) among individuals performing safety-sensitive work in industries.

Employee alertness depends not only on the number of hours worked, but also on a variety of other factors that include the worker’s specific job, individual circadian rhythm, quality of life, use of alcohol and drugs, and the physical, chemical, and psychosocial characteristics of the work environment. Although several of these factors are under the control of an employer, others are not. Thus, it is essential to enlist the entire workforce as active partners in managing risks associated with sleepiness. Increasingly, industry is moving away from pure hours-of-service standards toward a comprehensive risk management system designed to promote alertness, minimize sleepiness, identify evidence of drowsiness, and mitigate either the sleepiness itself or its potential consequences.

Occupational medicine physicians, whether directly employed by or serving as a consultant to an organization, have an important role to play in the risk management of sleepiness. Where no program is currently in place, physicians can and should advise management of the opportunities to enhance health, safety, and productivity through the development of a specific risk management system.