Modern agriculture is based on highly efficient equipment, especially high-speed, powerful tractors and agricultural machines. Tractors with mounted and trailed implements allow the mechanization of many agricultural operations.

Use of tractors allows farmers to accomplish the main tillage and care of plants in the optimum time without major manual labour. Permanent enlargement of farms, extension of land under cultivation and intensification of crop rotation promotes more efficient agriculture as well. Widespread use of high-speed assemblies is hampered by two factors: existing agricultural methods based mainly on machines and implements with passive tools; and difficulties in ensuring safe working conditions for the high-speed tractor assembly operator.

Mechanization can accomplish approximately 70% of planting and growing operations. It is used at all stages of crop cultivation and harvesting as well. Nevertheless, each stage of planting and growing has its own requisite set of machines, tools and environmental conditions, and this variability of the production and environmental factors has an influence upon the tractor driver.

Cultivation of the Land

Cultivation of the land (ploughing, harrowing, scuffing, disk harrowing, entire cultivation, rolling-down) is important and the most labour-intensive preliminary stage of crop production. These operations involve 30% of planting and growing operations.

As a rule, loosening of the soil results in the formation of dust. The nature of the dust in the air is variable, and depends on meteorological conditions, season, kind of work, type of soil and so on. Dust concentration in tractor cabs can vary from a few mg/m³ to hundreds of mg/m³, depending essentially on the cab enclosure. Approximately 60 to 65% of cases exceed the permissible total dust concentration level; permissible levels of respirable (less than or equal to 5 microns) dust are exceeded 60 to 80% of the time (see figure 1). Silica content in the dust varies from 0.5 to 20% (Kundiev 1983).

Figure 1. Tractor driver exposures to dust during land cultivation

Cultivation consists of power-consuming operations, especially during ploughing, and it demands a considerable mobilization of the power resources of machines, generating considerable levels of noise where tractor drivers sit. These noise levels amount to 86 to 90 dBA and higher, creating a considerable risk of hearing disorders for these workers.

As a rule, whole-body vibration levels where the tractor driver is seated can be very high, exceeding levels established by the International Organization for Standardization (ISO 1985) for fatigue-decreased proficiency boundary and frequently for exposure limit.

Ground preparation is conducted mainly in early spring and autumn, so the microclimate of cabs in temperate zones for machines without air conditioners is not a health problem except on occasional hot days.

Sowing and Growing

Ensuring that sowing attachments or ploughing implements move in a straight line and that tractors follow marker tracks or the middle of the row are characteristic features of the sowing and care of crops.

In general, these activities require the driver to work in uncomfortable positions and involve considerable nervous and emotional tension due to restricted working-zone visibility, resulting in rapid development of operator fatigue.

The layout of sowing machines and their preparation for use, as well as the necessity of manual auxiliary work, especially materials handling, may involve considerable physical loads.

A wide geographical distribution of grain varieties results in a diversity of meteorological conditions when sowing. Winter crop sowing for different climate zones can be performed, for example, when the outdoor temperature ranges from 3–10 °C to 30–35 °C. Spring crop sowings are performed when the outdoor temperature ranges from 0 °C to 15–20 °C. The temperatures in tractor cabs without air conditioners can be very high in regions where climate is mild and hot.

Microclimate conditions in tractor cabs are favourable as a rule during tilled crops sowing (sugar beet, maize, sunflower) in temperate zones. Cultivation of crops is performed when the outdoor temperature is high and solar radiation is intense. The air temperature in cabs without microclimate control can rise to 40 °C and more. Tractor drivers can work under uncomfortable conditions about 40 to 70% of the total time involved in the care of crops.

Working operations for tilled crops cultivation involve considerable moving of earth, causing formation of dust. Maximum ground dust concentrations in the breathing zone air do not exceed 10 to 20 mg/m³. The dust is 90% inorganic, containing a large amount of free silica. Noise and vibration levels where the driver sits are a little lower than those existing during cultivation.

During sowing and cultivation, workers can be exposed to manures, chemical fertilizers and pesticides. When safety regulations for handling these materials are not followed, and if machines are not working properly, the breathing zone concentration of hazardous materials can exceed permissible values.

Harvesting

As a rule, harvesting lasts from 25 to 40 days. Dust, microclimate conditions and noise can be hazards during harvesting.

Breathing zone dust concentrations depend chiefly on outside concentration and the airtightness of the harvesting machine’s cab. Older machines without cabs leave drivers exposed to the dust. Dust formation is most intensive during the harvesting of dry corn, when the dust concentration at non-enclosed combines’ cabs can be as much as 60 to 90 mg/m³. Dust consists mainly of plant scraps, pollen and mushroom spores, mostly in large, nonrespirable particles (larger than 10 microns). Free silica content is less than 5.5%.

Formation of dust during sugar beet harvesting is lower. Maximum dust concentration at the cab does not exceed 30 mg/m³.

Harvesting of grain is generally performed in the hottest season. Temperature in the cab can rise to 36 to 40 °C. The flux level of direct solar radiation is 500 W/m² and more when ordinary glass is used for cab windows. Tinted glass lowers the temperature of air in the cab by 1 to 1.6 °C. A mechanical forced ventilation system with a flow rate of 350 m³/h can create a temperature difference between inside and outside air of 5 to 7 °C. If the combine is equipped with adjustable louvers, this difference drops to 4 to 6 °C.

Tilled crops are harvested in the autumn months. As a rule conditions of the microclimate in cabs in this time are not a great health problem.

Experience in developed countries points to the fact that agriculture at small farms can be profitable with the use of small-scale mechanization (minitractors—motorized units with a capacity of up to 18 horsepower, with different kinds of auxiliary equipment).

Use of such equipment gives rise to a number of specific health problems. These problems include: intensification of workload in certain seasons, the use of child labour and the labour of elderly persons, absence of the means of protection against intensive noise, whole-body and local vibration, harmful meteorological conditions, dust, pesticides, and exhaust gases. The effort necessary to move the control levers of motorized units can amount to 60 to 80 N (newtons).

Some kinds of work are performed with the help of draught animals or done manually due to insufficient equipment or because of the impossibility of using machinery for some reason. Manual labour demands as a rule considerable physical effort. Power requirements during ploughing, horse-drawn sowing and manual mowing can amount to 5,000 to 6,000 cal/day and more.

Injuries are common during manual work, especially among inexperienced workers, and cases of plant burns, insect and reptile stings and dermatitis from the sap of some plants are frequent.

Prevention

One of the main trends in tractor construction is the improvement of working conditions of tractor operators. Side by side with perfection of the design of protective cabs is the search for ways of coordinating technical parameters of various tractor units with the functional abilities of operators. The aim of this research consists of ensuring the effectiveness of control and driving functions as well as necessary ergonomic parameters of the workplace environment.

Effectiveness of control and driving of tractor assemblies is ensured by good visibility of the working zone, by optimizing assemblies and control panel design and by proper ergonomic design of tractor seats.

Common ways of increasing visibility are increasing the viewing area of the cab using panoramic glass, improved layout of auxiliary equipment (e.g., fuel tank), rationalization of seat location, use of rear view mirrors and so on.

Optimization of construction control elements is connected with the construction of the control mechanism’s drive. Along with hydraulic and electric drives, a new improvement is suspended control pedals. This allows improved access and increased driving comfort. Functional coding (by means of form, colour and/or symbolic signs) plays an important part in recognition of the control elements.

Rational layout of instrumentation (which comprises 15 to 20 units in modern tractors) requires taking into account further increases in indicators due to remote control of technological process conditions, automation of the driving and operating of the technological equipment.

The operator’s seat is designed to guarantee a comfortable position and effective driving of the machine and tractor assembly. Design of modern tractor seats takes into account anthropometric data of the human body. Seats have adjustable back and arms and can be adjusted according to the operator’s size, in both horizontal and vertical dimensions (figure 2).

Figure 2. Angle parameters of optimal work posture of a tractor driver

Precautions against harmful working conditions for tractor drivers include means of protection against noise and vibration, microclimate normalization and airtight sealing of cabs.

Besides special engineering of the engine to reduce noise at its source, considerable effect is achieved by mounting the engine on vibration isolators, isolating the cab from the tractor body with the help of shock absorbers and a number of measures designed for absorption of noise in the cab. Flaky, sound-absorbing lagging with a decorative surface is applied for this purpose to cab wall panels, and rugs made of rubber and porolon are laid on the cab floor. Hard perforated panelling with an air gap of 30 to 50 mm is applied to the ceiling. These measures have reduced noise levels in cabs to 80–83 dBA.

The main means of damping low-frequency vibration in the cab is use of an effective seat suspension. Nevertheless, the effect of whole-body vibration damping achieved this way does not exceed 20 to 30%.

Agricultural ground levelling gives considerable opportunities for decreasing vibration.

Improvement of the microclimate conditions in tractor cabs is reached with the help of both standard equipment (e.g., fans with filter elements, thermo-insulating tinted glass, sun-proof cap peaks, adjustable louvers) and special devices (e.g., air conditioners). Modern tractor heating systems are designed as an autonomous assembly attached to the engine’s cooling system and using warmed water to heat the air. Combined air conditioners and air heaters are also available.

Complex solutions of the problem of noise, vibration and heat isolation and sealing of cabs can be reached with the help of sealed cab capsules designed with suspended control pedals and wire rope systems of drives.

Ease of access to tractor engines and assemblies for their maintenance and repairs, as well as obtaining timely information about technical condition of certain units of the assembly, are important indices of the level of tractor operator working conditions. Eliminating the cab bonnet, forward inclination of the cab, detachable panels of the engine’s bonnet and so on are available in certain types of tractors.

In the future, tractor cabs are likely to be equipped with automatic control units, with television screens for observation of implements that are out of the operator’s field of vision and with units for conditioning of microclimate. Cabs will be mounted on outside rotary rods so they can be moved to a required position.

Rational organization of work and rest is of great importance for the prevention of fatigue and diseases of agricultural workers. In the hot season, daily routine ought to provide for working mainly in the morning and evening hours, reserving the hottest time for rest. During exhausting work (moving, hoeing), short regular breaks are necessary. Special attention has to be devoted to the rational, balanced nourishment of workers with due regard for the energy requirements of the tasks. Drinking regularly during the heat is of great importance. As a rule, workers drink traditional beverages (tea, coffee, fruit juices, infusions, broths and so on) in addition to water. Availability of sufficient amounts of wholesome liquids of high quality is very important.

Availability of comfortable overalls and personal protection equipment (PPE) (respirators, hearing protectors), especially during contact with dust and chemicals, is very important as well.

Medical control of the agricultural workers’ health has to be oriented to prevention of common occupational diseases, such as infectious diseases, chemical exposures, injuries, ergonomic problems and so forth. Teaching safe working methods, information about matters of hygiene and sanitation are of great importance.

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Massive contamination of agricultural lands by radionuclides occurs, as a rule, due to large accidents at the enterprises of nuclear industry or nuclear power stations. Such accidents occurred at Windscale (England) and South Ural (Russia). The largest accident happened in April 1986 at the Chernobyl nuclear power station. The latter entailed intensive contamination of soils over several thousands of square kilometres.

The major factors contributing to radiation effects in agricultural areas are as follows:

• whether radiation is from a single or a long-term exposure

• total quantity of radioactive substances entering the environment

• ratio of radionuclides in the fallout

• distance from the source of radiation to agricultural lands and settlements

• hydrogeological and soil characteristics of agricultural lands and the purpose of their use

• peculiarities of work of the rural population; diet, water supply

• time since the radiological accident.

As a result of the Chernobyl accident more than 50 million Curies (Ci) of mostly volatile radionuclides entered the environment. At the first stage, which covered 2.5 months (the “iodine period”), iodine-131 produced the greatest biological hazard, with significant doses of high-energy gamma radiation.

Work on agricultural lands during the iodine period should be strictly regulated. Iodine-131 accumulates in the thyroid gland and damages it. After the Chernobyl accident, a zone of very high radiation intensity, where no one was permitted to live or work, was defined by a 30 km radius around the station.

Outside this prohibited zone, four zones with various rates of gamma radiation on the soils were distinguished according to which types of agricultural work could be performed; during the iodine period, the four zones had the following radiation levels measured in roentgen (R):

• zone 1—less than 0.1 mR/h

• zone 2—0.1 to 1 mR/h

• zone 3—1.0 to 5 mR/h

• zone 4—5 mR/h and more.

Actually, due to the “spot” contamination by radionuclides over the iodine period, agricultural work in these zones was performed at levels of gamma irradiation from 0.2 to 25 mR/h. Apart from uneven contamination, variation in gamma radiation levels was caused by different concentrations of radionuclides in different crops. Forage crops in particular are exposed to high levels of gamma emitters during harvesting, transportation, ensilage and when they are used as fodder.

After the decay of iodine-131, the major hazard for agricultural workers is presented by the long-lived nuclides caesium-137 and strontium-90. Caesium-137, a gamma emitter, is a chemical analogue of potassium; its intake by humans or animals results in uniform distribution throughout the body and it is relatively quickly excreted with urine and faeces. Thus, the manure in the contaminated areas is an additional source of radiation and it must be removed as quickly as possible from stock farms and stored in special sites.

Strontium-90, a beta emitter, is a chemical analogue of calcium; it is deposited in bone marrow in humans and animals. Strontium-90 and caesium-137 can enter the human body through contaminated milk, meat or vegetables.

The division of agricultural lands into zones after the decay of short-lived radionuclides is carried out according to a different principle. Here, it is not the level of gamma radiation, but the amount of soil contamination by caesium-137, strontium-90 and plutonium-239 that are taken into account.

In the case of particularly severe contamination, the population is evacuated from such areas and farm work is performed on a 2-week rotation schedule. The criteria for zone demarcation in the contaminated areas are given in table 1.

Table 1. Criteria for contamination zones

When people work on agricultural lands contaminated by radionuclides, the intake of radionuclides by the body through respiration and contact with soil and vegetable dusts may occur. Here, both beta emitters (strontium-90) and alpha emitters are extremely dangerous.

As a result of accidents at nuclear power stations, part of radioactive materials entering the environment are low-dispersed, highly active particles of the reactor fuel—“hot particles”.

Considerable amounts of dust containing hot particles are generated during agricultural work and in windy periods. This was confirmed by the results of investigations of tractor air filters taken from machines which were operated on the contaminated lands.

The assessment of dose loads on the lungs of agricultural workers exposed to hot particles revealed that outside the 30 km zone the doses amounted to several millisieverts (Loshchilov et al. 1993).

According to the data of Bruk et al. (1989) the total activity of caesium-137 and caesium-134 in the inspired dust in machine operators amounted to 0.005 to 1.5 nCi/m³. According to their calculations, over the total period of field work the effective dose to lungs ranged from 2 to
70 cSv.

The relation between the amount of soil contamination by caesium-137 and radioactivity of work zone air was established. According to the data of the Kiev Institute for Occupational Health it was found that when the soil contamination by caesium-137 amounted to 7.0 to 30.0 Ci/km² the radioactivity of the breathing zone air reached 13.0 Bq/m³. In the control area, where the density of contamination amounted to 0.23 to 0.61 Ci/km³, the radioactivity of work zone air ranged from 0.1 to 1.0 Bq/m³ (Krasnyuk, Chernyuk and Stezhka 1993).

The medical examinations of agricultural machine operators in the “clear” and contaminated zones revealed an increase in cardiovascular diseases in workers in the contaminated zones, in the form of ischaemic heart disease and neurocirculatory dystonia. Among other disorders dysplasia of the thyroid gland and an increased level of monocytes in the blood were registered more frequently.

Hygienic Requirements

Work schedules

After large accidents at nuclear power stations, temporary regulations for the population are usually adopted. After the Chernobyl accident temporary regulations for a period of one year were adopted, with the TLV of 10 cSv. It is assumed that workers receive 50% of their dose due to external radiation during work. Here, the threshold of intensity of radiation dose over the eight-hour work day should not exceed 2.1 mR/h.

During agricultural work, the radiation levels at workplaces can fluctuate significantly, depending on the concentrations of radioactive substances in soils and plants; they also fluctuate during technological processing (siloing, preparation of dry fodder and so on). In order to reduce dosages to workers, regulations of time limits for agricultural work are introduced. Figure 1 shows regulations which were introduced after the Chernobyl accident.

Figure 1. Time limits for agricultural work depending on intensity of gamma-ray  radiation at workplaces.

Agrotechnologies

When carrying out agricultural work in conditions of high contamination of soils and plants, it is necessary to strictly observe measures directed at prevention of dust contamination. The loading and unloading of dry and dusty substances should be mechanized; the neck of the conveyer tube should be covered with fabric. Measures directed at the decrease of dust release must be undertaken for all types of field work.

Work using agricultural machinery should be carried out taking due account of cabin pressurization and the choice of the proper direction of operation, with the wind at the side being preferable. If possible it is desirable to first water the areas being cultivated. The wide use of industrial technologies is recommended so as to eliminate manual work on the fields as much as possible.

It is appropriate to apply substances to the soils which can promote absorption and fixation of radionuclides, changing them into insoluble compounds and thus preventing the transfer of radionuclides into plants.

Agricultural machinery

One of the major hazards for the workers is agricultural machinery contaminated by radionuclides. The allowable work time on the machines depends on the intensity of gamma radiation emitted from the cabin surfaces. Not only is the thorough pressurization of cabins required, but due control over ventilation and air conditioning systems as well. After work, wet cleaning of cabins and replacement of filters should be carried out.

When maintaining and repairing the machines after decontamination procedures, the intensity of gamma radiation at the outer surfaces should not exceed 0.3 mR/h.

Buildings

Routine wet cleaning should be done inside and outside buildings. Buildings should be equipped with showers. When preparing fodder which contains dust components, it is necessary to adhere to procedures aimed at prevention of dust intake by the workers, as well as to keep the dust off the floor, equipment and so on.

Pressurization of the equipment should be under control. Workplaces should be equipped with effective general ventilation.

Use of pesticides and mineral fertilizers

The application of dust and granular pesticides and mineral fertilizers, as well as spraying from aeroplanes, should be restricted. Machine spraying and application of granular chemicals as well as liquid mixed fertilizers are preferable. The dust mineral fertilizers should be stored and transported only in tightly closed containers.

Loading and unloading work, preparation of pesticide solutions and other activities should be performed using maximum individual protective equipment (overalls, helmets, goggles, respirators, rubber gauntlets and boots).

Water supply and diet

There should be special closed premises or motor vans without draughts where workers can take their meals. Before taking meals workers should clean their clothes and thoroughly wash their hands and faces with soap and running water. During summer periods field workers should be supplied with drinking water. The water should be kept in closed containers. Dust must not enter containers when filling them with water.

Preventive medical examinations of workers

Periodic medical examinations should be carried out by a physician; laboratory analysis of blood, ECG and tests of respiratory function are compulsory. Where radiation levels do not exceed permissible limits, the frequency of medical examinations should be not less than once every 12 months. Where there are higher levels of ionizing radiation the examinations should be carried out more frequently (after sowing, harvesting and so on) with due account of radiation intensity at workplaces and the total absorbed dose.

Organization of Radiological Control over Agricultural Areas

The major indices characterizing the radiological situation after fallout are gamma radiation intensity in the area, contamination of agricultural lands by the selected radionuclides and content of radionuclides in agricultural products.

The determination of gamma radiation levels in the areas allows the drawing of the borders of severely contaminated areas, estimation of doses of external radiation to people engaged in agricultural work and the establishing of corresponding schedules providing for radiological safety.

The functions of radiological monitoring in agriculture are usually the responsibility of radiological laboratories of the sanitary service as well as veterinary and agrochemical radiological laboratories. The training and education of the personnel engaged in dosimetric control and consultations for the rural population are carried out by these laboratories.

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