ارزیابی های ارگونومیک و مقایسه سیستم های جمع آوری چوب در شمال غرب روسیه

A comparison of 14 currently applicable wood harvesting systems was assessed with respect to ergonomic point of view. For this purpose, the research method, based on the Hodges–Lehmann rule and the integrated work-severity rate of single machinery, was developed for ergonomic evaluation of cut-to-length, tree-length and full-tree harvesting systems. Altogether, about 130 different parameters of 36 units of equipment that impact on the ergonomics and work conditions were measured and estimated in interviews undertaken directly at forestry harvesting workplaces in 15 logging companies in the Republic of Karelia, Northwest Russia. Then the results were compared to the effective norms, and the degree of compliance with the stipulated values was determined. The estimates obtained for the degree of compliance were combined. This permits a direct comparison of the workload on forestry harvesting workers such as operators, lumberjacks and choker setters. In many respects, the current ergonomic standard is standard, except for the operators of cable skidders, chainsaws and choker settings. Visibility and work postures were considered to be the most critical features influencing the operator's performance. Problems still exist, despite the extensive development of cabs. The best working conditions in terms of harvesting systems were provided by “harvester + forwarder” in cut-to-length harvesting, and “feller–buncher + grapple skidder” in full-tree harvesting. The motor-manual tree-length harvesting performed with cable skidders showed the worst results in terms of ergonomics.

Full-tree (FT), tree-length (TL) and cut-to-length (CTL) methods, and associated harvesting systems usually are applied in wood harvesting. These methods differ in relation to the technology utilised. The FT method is globally the most common method. FT harvesting means that the trees are felled and the stem, intact with branches, is initially transported to the roadside landing using a skidder. Delimbing and, if necessary, bucking are performed at the roadside. In the TL method, trees are delimbed immediately after felling, and then the intact stems are skidded to the roadside landing. The tree-lengths, in both methods, are then transported by tree-length trucks or trains to the central processing yard or wood-processing mill, where they are bucked into timber assortments. If the bucking is performed at the roadside terminal, the assortments are directly transported by short-wood trucks to the wood-processing mill. The third method, cut-to-length, means that the trees are processed (delimbed and bucked) into timber assortments in conjunction with the felling operations. Then the assortments are extracted with forwarders to the roadside where they are piled to await secondary transport by short-wood trucks to the wood-processing mill. Each of the harvesting methods also has its specific features that depend on natural and production conditions, the technology used, and the share of manual operations in the overall process. Thus, depending on the level of mechanisation and the type of equipment used, all the identified harvesting systems can be divided into the following most typical groups in Russia (Gerasimov and Seliverstov, 2010): 1. Fully mechanised CTL harvesting: felling, processing (delimbing and bucking) with a harvester, and extraction with a forwarder: FM CTL (harvester + forwarder); 2. Motor-manual CTL harvesting: felling, processing with a chainsaw, and extraction with a forwarder: MM CTL (chainsaw + forwarder); 3. Motor-manual TL harvesting: felling with a chainsaw, delimbing with a chainsaw/axe, and extraction with a cable skidder: MM TL (chainsaw + skidder); 4. Fully mechanised FT harvesting: felling with a feller buncher, extraction with a grapple skidder, and processing with a processor: FM FT (feller buncher + skidder + delimber/processor); 5. Motor-manual FT harvesting: felling with a chainsaw, extraction with a cable skidder, and processing with a delimber: FT (chainsaw + skidder + delimber). The efficiency and functionality of a particular wood harvesting system depend on a number of characteristics. The economic benefits can be evaluated by such indicators as labour, productivity and cost. Environmental indicators can include soil damage (the rut depth or the degree of soil compaction), damage to undergrowth or remaining trees, etc. The wood quality indicators are determined by evaluating the quality of the timber in accordance with the quality specifications in the customer contracts, as well as other quality requirements. Undoubtedly, work safety and ergonomics cannot be ignored when comparing different technologies. Wood harvesting has been associated with high accident risk due to the low level of mechanisation, especially with a fatal outcome; the latter has been estimated at 1.4 deaths per 1 million m3 cut in Russia (Gerasimov and Karjalainen, 2008). Recently, special attention has been paid to comfortable and safe working conditions in forest operations (Hanse and Winkel, 2008; Smidt, 2011; Synwoldt and Gellerstedt, 2003). This will make harvesting work more attractive to the young, and employment in a logging company more desirable. Ergonomic indicators describing the work severity (noise and vibration levels, visibility, etc.) can be used to evaluate the safety and comfort of the work (Hansson, 1990; Harstella, 1990). Some studies in ergonomics of logging operations have been conducted in Russia during the Soviet time (Byzov, 1985; Oblivin et al., 1988; Vasekin et al., 1991) and are still conducting today in Russia at Voronezh Forest Engineering Academy (e.g., Kondrashova, 2010; Posharnikov et al., 2012), Petrozavodsk State University (e.g., Kukelev and Ustinov, 2005; Sokolov, 2008; Sokolov et al., 2008, 2012; Syunev et al., 2009; Gerasimov et al., 2008) and some others (e.g., Korenevsky et al., 2009). A positive result of the mechanisation of harvesting work is the drastic reduction in serious accidents and injuries (Axelsson, 1998; Lefort et al., 2003; Potočnik et al., 2009; Sokolov et al., 2008). However, increasing mechanisation is posing new problems. Operators of harvesting machinery are being afflicted by overload injuries to the neck, arms and cervical spine. The main causes of these injuries are probably excessive periods of sitting, excessive work intensity during work in fixed, ergonomically-inappropriate positions, and repetitive, short-cycle movement patterns. Moreover, the motor-manual harvesting systems, using chainsaws, choker settings and primitive cable skidders, still continue to be widely used in forest operations due to steep and wet terrains and the difficult social-economic conditions in many countries, such as Russia. Due to the ergonomic feasibility of harvesting operations being a critical element for the development of wood harvesting, using a number of different harvesting systems, such as MM FT, FM FT, MM CTL, FM CTL and MM TL, the main objective of the study was to evaluate and compare the most applicable currently used harvesting systems in terms of ergonomics.

Similar papers are published in the Nordic countries and Ireland for CTL harvesting (e.g., Synwoldt and Gellerstedt, 2003; Gellerstedt et al., 1999; Grevsten and Sjögren, 1996; Hanse and Winkel, 2008; Harstela, 1990; Sherwin et al., 2004; etc.), in New Zealand, Canada and the USA for FT harvesting (e.g., Bentley et al., 2002; Bentley et al., 2005; Golsse, 1994; Kirk and Sullman, 2001; Murphy and Oliver, 2011; Parker, 2010; Sirois and Smith, 1985; Smidt, 2011; Zerbe, 1979; etc.), also the EU-project ErgoWood (http://www.enfe.net/pberichte_e.htm) and its implementation project COMFOR (http://enfe.net/comforopen/comfor.htm). However, no scientific reports concerning the comparison of ergonomic performance for wood harvesting systems have been found neither in Russia, nor other countries. The research method examined based on the Hodges–Lehmann rule and the integrated work-severity rate of single machinery is perhaps the first attempt to evaluate and compare the ergonomic performance of different wood harvesting systems. Multi-criteria decision making with the Hodges–Lehmann rule was used in ergonomic evaluation of wood harvesting systems. The method combined qualitative and quantitative information about ergonomic indicators of individual machines. Each alternative in our multi-criteria decision making problem was described by a set of ergonomic indicators and criteria. They are qualitative and quantitative, having different units of measurement and different optimization direction. The normalization of criteria values is needed in this problem with an aim to obtain comparable scales of criteria values. The present research was focused on introducing this method for decision making normalization. The results show an efficiency of the method due to taking into account many different factors, a large number of measurements, as well as a combination of measuring methods with questionnaires. The use of the Hodges–Lehmann rule allows making a comparison of not only individual harvesting machines, but their systems too. The total work-severity rates for the machines and equipment studied were obtained in a field study and by interviews, and should be improved on in the future due to the study being conducted in only one region in Northwest Russia. Additional ergonomic factors have to be involved in severity rate estimations, such as temperature, humidity, ventilation, and carbon dioxide concentration. When this approach can be used in other climate conditions, for example, tropical forests. Other types and models of applicable machinery, such as chippers, energy wood harvesters, loaders, etc., need to be taken into account due to the number of applicable harvesting systems (over fourteen studied systems appear in this paper) especially with respect to wood-to-energy systems. The results of the measurements obtained at the forestry harvesting works may be helpful in the evaluation of the ergonomic performance of single machinery within the similar harvesting methods and systems in other countries. However, the national or ISO-standards should have to use instead of the Russian national ergonomic standards. The further method development might be the increasing number of the estimated ergonomic factors. For example, the method should include the full range of the micro-climate factors such as temperature and humidity in different areas of workplace, the content of various contaminants in inhaled air, etc. The measurement of these parameters in the forest is associated with challenges and requires more time and labour, and the special equipment. In addition, these factors are highly dependent on external conditions that cannot be the same in different harvesting areas located far away from each other. For these reasons, some factors were excluded from the method used, although, of course, it is not desirable. But in spite of all the above, the results might be useful for forestry companies to justify the selection of harvesting technology and systems of machines based not only on technical and economic factors, but also on the working conditions of personnel involved.