فرشته رحیمی بی تم

Chainsaws, which are widely used in tree felling operations, create vibrations. Long-term and intense exposure to vibration may lead to the development of vascular, neurosensory, and musculoskeletal disorders in the upper limbs of chainsaw workers, known as Hand-arm vibration syndrome. This study investigates the vibration levels during tree bucking operations on poplar trees with the MPTMGS5803 chainsaw model, one of the most widely used chainsaws in forest operations in the western part of Guilan province. Simultaneous vibration measurements in three directions (x, y and z) were carried out using the SVANTEK 106A vibration meter, aiming to determine the total amount of chainsaw vibration and the daily exposure period. The results show that the highest amount of vibration was measured in the x (1.61±0.62), (2.01±0.90) direction and the lowest in the y (1.48±0.17), (0.73±0.09) direction both in the rear handle and front handle of the chainsaw. The rear handle of the chainsaw had a higher overall vibration acceleration (3.05±0.54 m/s2) compared to the front handle (1.94±0.53 m/s2). In terms of the daily exposure period, the level of vibration exposure inflicted on the chainsaw operator during a  three-hour and 70 second working period amounted to 1.19 m/s2 in the front handle and 1.87 m/s2 in the rear handle, with both values falling within the permissible vibration range.

Nowadays, chainsaws remain the primary main tool for wood harvesting in the world due to their multifunctionality and the relatively low requirements in financial investment. Another reason is that chainsaws provide high workability, enhancing efficiency and productivity, at reduced felling costs. The felling of poplar stands in the west of Guilan Province is carried out semi-mechanically using chainsaws within a clear-cutting silviculture system. Productivity and cost are two main factors that affect the selection of wood harvesting systems, whose tree felling consists an element of paramount importance, most notably its duration. The purpose of this study was to assess the productivity and cost of clear-cutting operations in a poplar plantation located in the western part of the Guilan Province, using the MASHOUF PSI 9700, a short-bladed chainsaw model with a bar length of 50 cm.

The research was conducted in the Tanyan district, which is located in the western part of Guilan province. A work team, consisting of a chainsaw operator and a helper, was used during the study. The selected work team was chosen as representative of the average skill level of the workers in the region. The chainsaw selected for this research, the MASHOUF PSI 9700 model featuring a cylinder displacement of 54 cm3 a power output of 2.2 KW, and a weight of 5.1 kg excluding equipment, had been in operation for about 2000 hours, which is the average life span of a product of this category. Over the years, the research on consumption time has focused especially on establishing the relationship between work efficiency and productivity carried out considering various equipment and wood harvesting factors. Analysis of work time consumption and productivity in chainsaw operations is an important concern of sustainable harvest management. A time study was performed to calculate the hourly productivity rate. Felling time was classified into two categories, namely effective time and delay time. Effective time consisted of (a) Moving towards the tree, (b) Felling preparation, (c) Under cut, (d) Back cut and (e) Refueling. Moreover, the delay times fell into (a) Rest time or personal time, (b) Operational delays, and (c) Technical delays. The total fixed cost was obtained considering the chainsaw purchase value, the sum of the annual investment, the depreciation, the insurance and taxes. Variable costs were also calculated considering the hourly expenditure on fuel cost, maintenance as in the cases of chain and sprocket replacement, etc. The sum total of costs included fixed, variable and labor costs. The data was initially processed using Excel 2013 software and then analyzed using the SPSS statistical software version 18 to determine the distribution and ratio of work interruption time according to the factors affecting it. Regression analysis was conducted to explore the relationship between the factors affecting the total cut-off time.

A total of 133 trees were felled amounting to a volume of 109.06 m3. The total work time consumed for felling operations was 500.21 minutes. Of the total working time, 41.42% was allocated to main work tasks. Supplementary work, such as moving between trees and driving wedges, accounted for 8.84% of felling time, while preparatory tasks, including moving between workplaces and preparation activities, constituted 15.29%. Repair time accounted for 9.60% of the total time, while delays and downtime occupied 15.74%. Additionally, 9.09% of the time was spent on non-workplace activities. The majority, 71% of the delays were linked to personal delays, of which 80.7% were related to lunchtime breaks and 19.93% to other personal delays. Operational and technical delays accounted for 10% and 19% of total delays, respectively. Increases in the diameter of the felled trees, resulted in increases to both the net felling time and the net production of the felling team. Furthermore, an increase in the diameter decreased the production cost. The results showed that the average time consumed per tree for felling were 2.73 min of effective time vs 3.75 min of gross time, and net hourly productivity amounted to 17.28 m3 per hour vs 13.44 m3 per hour found for the gross hourly productivity, and the unit cost of net production was 0.25 USD vs 0.32 USD for the gross production, respectively. The statistical analysis exhibited a highly significant correlation between work element times (measured in minutes) and various factors, including the diameter of the tree at breast height, tree volume (measured in m3), and the distance between trees (measured in m).

By developing mathematical models of working time for various chainsaw models, chainsaws, the performance of the felling teams can be increased, and a more equitable remuneration of the forest workers is made possible. The results of the present study can support decision making regarding the work rates, work schedules, and cost estimation. The models and results presented in this study can generally assist forest managers to better understand the factors affecting productivity and cost during different work elements with the aim to reorganize and plan forest work to meet economic concerns.