Chernyuk, Vladimir Ivanovich
Institute for Occupational Health / 75 Saksagansky St. / Kiev 01033, Ukraine
380 44 2208030 / holia@mail.iptelecom.net.ua
Bobko, Natalia Andreyevna
Institute for Occupational Health / 75 Saksagansky St. / Kiev 01033, Ukraine
380 44 2204605 / natalia@ioh.freenet.kiev.ua
Tkachenko, Olga Mikhaylovna
Institute for Occupational Health / 75 Saksagansky St. / Kiev 01033, Ukraine
380 44 2204422 / holia@mail.iptelecom.net.ua
ABSTRACT
Valid legislation on ergonomic standardisation of workplace factors had been elaborated based mainly on investigations conducted during the daytime. However, many researches prove decreased adaptation body’s possibilities regarding environmental factors at night compared to day shifts while the same ergonomic standards have been applying for all shifts. Some steps have been undertaken to improve the acting legislation (EU Directive 1993, OSHA 1973). At the same time, known gap exists between standards and practice. In addition, specific pronounced effects of some time-of-day periods are shown. Developing countries manifest aggravated problems. Up-to-date evidences are sufficient to raise the question on the improvement of ergonomic standards considering circadian regularities in functioning of a human body that should be based on complex physiological and ergonomic studies taking into account as many effective factors as available.
Keywords
Shiftwork, ergonomic standardisation, workplace factors
INTRODUCTION
About 20% of working people, according to the statistical data, are being involved into night and shift work. In this, the requirements of the society in shiftwork as well as its spreading increase every year. However, morbidity and labour turnover is shiftworkers are higher compared to day workers. Every fifth worker is not able to tolerate working in a shift regime and has to leave it because of health and/or social/family problems. Complaints of sleep disorders, diseases of gastrointestinal tract (chronic gastritis, gastric and duodenal ulcers are recorded in them 2-8 times often than in day-time workers), neuropsychic disorders (chronic nervousness and depression), cardiovascular diseases (ischemic heart disease, hypertension) are proven to be predominant occupational health risks of shiftworkers [5,6,13].
MAIN PART
In accordance with Hygienic Labour Classification adopted in Ukraine shift work assuming work in 2 shifts (without night shift) is estimated as permissible; shift work including night work is estimated as harmful (1st degree tension (Class 3.1) or in the case of irregular work under shift rotation – as 2nd degree tension (Class 3.2). According to Labour Code night time is the time from 22 p.m. to 6 a.m. Night
work should be paid more. Taking into account that night work affects women, adolescents and elderly people in the most negative manner, the involvement of these categories into night works is restricted by the legislation.
Employees of operator’s professions often are working under unfavourable productive environment.
For example, increased levels of noise and temperature in the working zone (Class 3.1) are typical deviations from ergonomic norm as for control room workers at the heat power plants [14]. Deficient work experience is specific characteristic of this professional group: workers often leave this occupation after they reach 40 years old irrespectively the prestigious salary.
Workplace exposures of the operating personnel working at radio-technical equipment of surveying radio-location sets, systems of short-range navigation, radio-technical units of landing services are classified as harmful (Class 3.3) by the levels of electromagnetic fields and noise. Hypertension is recorded in almost 30% of such workers after they reach 40-49 years old. At the same time among air traffic controllers whose work conditions are classified as harmful (Class3.3) mainly due to high neuroemotional tension, hypertension is recorded in 9% cases. Effects of unfavourable workplace factors on air traffic controllers are considered to be regulated through strict occupational selection [17].
Valid legislation on ergonomic standardisation of workplace factors had been elaborated and formed based mainly on investigations conducted during the daytime. At the same time, today there are a lot of evidences for different character of the body’s reply to the same influences at different times of day or night.
Daily fluctuations in body susceptibility to different chemical substances, regularities in their metabolism and elimination are known. Under the same concentrations of acetone in the working zone air the acute symptoms of discomfort (dizziness, nausea), irritation (of mucous membrane of nose, mouth and throat) and difficulties in breathing at the end of night shifts are more pronounced than in the end of morning or evening shifts, in the end of evening shifts – also more pronounced as compared to the end of morning shifts [10]. Pharmacological substances, which are used for treatment of acute and chronic diseases, can effect the body differently depending on the time of their intake [5]. So, chronotoxic and chronopharmacological risks in shift workers are proven to be higher as compared to day workers.
Working under heating microclimate at the day shifts caused the increase in daily average body temperature when working zone air temperature was 37°C and higher, while for night shifts it became higher beginning with 29°C [11]. So, body’s adaptation resources regarding work environmental temperature fluctuations at night time are narrow as compared with that of the day time and unfavourable effects of increased temperature on shiftworkers at night is higher than that in the daytime, while the applied ergonomic standards are the same.
Night work cause increased excretion levels of potassium, urinary acid, glucose, cholesterol, total lipids in repair crew workers at railway station as compared to the day shift excretion, thus reflecting the catabolic body’s response at night shift [20]. As a result of significant increase in mental workload on air traffic controllers the excretion of catecholamines during morning and evening shifts increases, mainly due to adrenaline, at night time – due to noradrenaline, thus showing the change of metabolism from normal carbon type (at the day time) to unfavourable lipid type (at night) [8]. Fatigue accumulation in electricity distribution network controllers at the second consecutive 12-hour day shifts results in changes of blood circulation self-regulation towards a vascular type, at night shifts – into cardiac type, whereas the norm is the mixed type [3]. Systematic changes in basic regulatory mechanisms could cause shiftworkers’ health problems in time.
Fatigue at night shifts is higher compared to daytime [7,12]. The highest risk of accidents is observed at night and their consequences are the most difficult [7,16].
The largest accidents – at the Chernobyl nuclear power plant, at the chemical enterprise in Bhopal, at the Three-Miles Iceland nuclear unit and the oil tanker “Axon Valdez” – have happened at night or early morning hours. At 4 o’clock in the morning when many physiological functions are at the minimal activity level the relative risk of single vehicle accidents is 35 times higher than in the day time [9].
Different character of response to the same exposures at different times of day and night is the subject of circadian body clock activity that is “tuning” by fluctuations of geophysical factors and directed to provide active interaction of the body with the environment at the day time while at night – to adopt the information obtained during a day, to provide rest and self-recovery for the body. This is one of the basic body characteristics that is being underestimated in a systematic manner in ergonomic standardisation. Its significance in some sense could be compared to the workload in professions of high nervous-emotional tension: effects of time-of-day and workload in air traffic controllers make approximately the same inputs into fatigue development [18].
Some steps are being undertaken to correct acting legislation regarding ergonomics standardisation considering circadian fluctuations in body reactions to these or those exposures. Since 1993 the following Directive is in force in the European Union: “night workers whose work involves special hazards or heavy physical or mental strain do not work more than 8 hours in any period of 24 hours during which they perform night work”. In Ukraine socially attractive 12-hour shifts have been using in such occupational groups as well. At the same time their negative effects on cardiovascular system activity, efficiency and safety of work have been shown [1,15,19]. To improve shift schedules it is necessary to conduct physiological and ergonomic studies with due account of specific features of the working process, time and efforts needed for a way to and from work of each specific enterprise, employment of workers at extra works as well as social needs of workers (the need to visit children establishments, libraries, sport halls, etc.) and the life standards of the population in a particular area.
As regards work place factors of physical and chemical nature the time-of-day correction of ergonomic standardisation is not practically going on.
Another important characteristic of shiftwork is the use of non-standard duration of a working shift – more or less than 8 hours. Medical workers and security workers, for example, are on duty for 24 hours, dispatchers and controllers at transport and in power engineering are involved into 12-hour shifts whereas sailors of far navigation are keeping 4-hour watches.
By the Code of Labour the normal duration of a work time should not exceed 40 hours a week. The normal duration of a workday is 8 hours. Maximum permissible duration of a workday should not exceed 10 hours even in such branches of national economy where there are substantial differences in organisation of production and labour (timber industry and forestry, agriculture, etc.). In exceptional cases featured by work conditions the range of 12 hours is permitted as the maximum shift duration. However, while elaborating the shift schedules the problematicity of long working hours should be of a particular concern because of health problems for workers and production safety problems: after 8 hours of continuous work the number of mistakes increases [1] and physiological maintenance of professional activity becomes more difficult [2] having long-term negative effects on health and safety [15,19].
The involvement into overtime works requires the consent of a worker and, sometimes, of the trade union committee. Overtime work should be paid more: for first 2 hours of work – no less than one and a half of the salary; for successive hours – no less than double payment. Overtime works should not exceed 4 hours for a worker within 2 successive days and 120 hours a year.
Since 1979 the OSHA standards are being in force in the USA providing for decrease of exposure levels of chemical factors proportionally to the increase of duration of its exposure (again, no time-of-day effect is considered). The same
concerns factors of physical nature. Generally accepted standards in Ukraine have been estimated for standard 8-hour duration of a working shift. The problem of adequate correction of permissible exposure levels (PEL), threshold limit values (TLV), maximal allowable concentration (MAC) under changes in shift duration when keeping to or when increasing standard duration of a working week and working month for factors of different nature requires additional investigations, which should be based on the evaluation of actual effects of workplace factors on the body under corresponding risk assessment as applied to evening and night shifts. Factors of ionising and non-ionising radiation need a particular attention. There are no organs of sense in humans susceptible to electromagnetic and radioactive rays (except of their visible range), thus making these effects especially harmful.
In a number of occupations high work tension caused the necessity to shorten the intervals of continuous fulfilment of professional duties by workers within a working shift. In air traffic controllers at large airports the uninterrupted work related to air traffic movement should not exceed 2 hours with a 20-minute brake afterwards. In small airports, even in case of a very low air traffic intensity (e.g. one air craft per 2 hours), intervals of uninterrupted work should not exceed 4 hours. The exceeding of established intervals is followed by increased fatigue [18] and could cause increase in the probability of mistakes with all corresponding after-effects related to flight safety.
The time of beginning and ending of a shift is also of a great significance. The beginning of a shift at very earlier time is accompanied by high incidence of traumatism and accidents whereas it’s ending at very late time in the evening – by high fatigue. It is found that fatigue at 4-6 o’clock in the morning is expressed 1,7 times more than at 6.00-8.00 p.m. [18]. Thus, 4.00-6.00 a.m. should be considered as the most unfavourable time to start or finish a work shift and 6.00-8.00 p.m. – is the most favourable time for shift changing under round-the-clock industry.
Under workload increase the activity of systems of neurohumoral regulation and the general work capacity, including muscular one, raises. So, in the case of a sedentary mental work there occurs a problem of dissolution of developed metabolic changes. If not settled positively psychic and psychosomatic disorders could be developed in workers in time. So, it is very important to pay attention to rest intervals during the work and to physical exercises. However, for night shifts it is correct from physiological point of view to decrease all possible types of activity due to decrease in the level of functioning of the majority of systems and organs. So, deep at night it is not recommended to perform physical exercises, take food or have any other additional loads. Night works, to much extent, aggravate the problem of dissolution of metabolic changes occurring as a result of high workload.
Additional steps have to be undertaken to improve acting ergonomic standardisation regarding mentally tensive night and shift work.
In Ukraine the changes in the structure of agro-industrial complex, building new enterprises with various types of property such as private, cooperative, family-like, etc. resulted, first of all, in changes in work conditions and in agricultural workers’ health.
The work of employees in agrarian sector is one of the most complicated from the point of view of ergonomic standardisation because of its seasonal character for main occupations and due to the excess of permissible duration of a working day (10 hours). Under spring and summer works as well as during harvesting, workers are on duty not only during the light day, but at night as well that disorders normal sleep and rest.
Under developing economy the use of outdated technologies, equipment and agricultural machinery (when their moral and technical wear exceeds 80%) aggravates this problem. The high percent of manual work, significant domestic
loads against the background of low life standards contribute to additional risk of development of work-related and occupational diseases.
In recent years the process of development of country farming with participation of members of families and relatives is actively under way. However, hired workers are often being involved into spring-summer field works and harvesting and they are often the most unprotected social group.
Under transitional period of economy development the duration of a working day becomes a value of insufficient control due to poor work productivity as a whole - on the one part, and meeting wishes of an employer to produce more and a hired worker to earn more - on the other part.
The third important aspect among problems of ergonomic standardisation regarding shift works are individual differences in workers related, first of all, to their sexual and age characteristics. Thus, it is known, that women suffer more from shift work as the quality of sleep in them is worse (as compared with men) due to their menstrual cycle. Spontaneous abortions, premature delivery, low fetus weight, complications in menopause are recorded in them more often than in women working by ordinary schedule [6]. Social desynchronising factor in women is pronounced more vividly than in men because of everyday duties on domestic affairs and care of children and family members who live according to normal daily regime. On the other hand, with age, after 40 years old, the possibility to work at night worsens because of gradual decrease of melatonin production (a natural sleeping substance in the body) and, with this in due, the deficiency in sleep increases (the first complaint of shift workers) against the background of gradual age increase of general adaptation body reserves. Night and continuous works have very harmful effects on the body of adolescents (which have not yet been developed) as they hamper normal body growth and formation. So, its necessary to work out special favourable work and rest schedules considering circadian regularities in body activity for night and shift workers aged after 40 as well as for women and adolescents.
CONCLUSION
So, by present, there is available sufficient number of evidences to raise the question on the actuality to conduct studies in order to make the amendments into acting legislation concerning night and evening shifts. In economically developed countries the correction of duration of night shifts is used depending on work tension as well as the correction of the dose (level) of exposure to factors of physical and chemical nature depending on duration of their exposure (duration of a work shift, irrespectively time of day). However, further systematic studies on circadian changes in the effects of specific factors of physical or chemical nature, work tension in shift and night workers of various occupational groups (first of all in high reliability organisations (man-machine and man-man systems where the role human(-operator) is high (transport, energetics, large technological objects, service sector, urgent medicine, etc.)), in the case of the high labour turnover, deficiency of work experience in the occupation and the pronounced morbidity) are needed. The improvement of ergonomic standardisation aiming to decrease occupational risk in shiftworkers requires the correction of the acting legislation considering circadian regularities in body activity, which should be based on complex physiological and ergonomic studies with due account of as many effective factors as possible as well as workers’ individual differences, on sexual and age characteristics, first of all.
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