ANALYSIS OF THE TIME OF EXPOSURE TO NOISE OF THE VIMEK 606 6WD FORWARDER OPERATOR IN SELECTED CONDITIONS OF PILE TIMBER FORWARDING

Piotr S. Mederski¹, Mariusz Bembenek¹, Leszek Hoffman^2
1 Department of Forest Utilisation, August Cieszkowski Agricultural University of Poznan, Poland
² Research and Development Centre of State Forests in Bedon, Poland

ABSTRACT

The performed analyses comprised the time of exposure to acoustic loads of the operator of the Vimek 606 6WD forwarder during the forwarding of pile timber harvested using two methods: with and without a midfield. Timber intended for forwarding was harvested with the Timberjack 770 harvester employing one of the following two technologies: 1/ with a midfield – the spacing of strip roads exceeds two times the range of the harvester crane; 2/ with strip roads (without the midfield) with distances between them not greater than twice the range of the harvester crane. The alternative method of timber harvest <footnote>, in which more raw material was gathered close to the skid road, allowed reducing the proportion of driving time needed by the harvester during timber forwarding. The stacked wood was forwarded with the Vimek 606 6WD forwarder. In each of the treatments, the time of exposure of the harvester operator to noise was investigated.

In the course of the performed experiments, using the Bruel & Kjaer 2231 audiometer, the noise intensity was measured in the closed cabin of the forwarder during the following two operations: timber loading (85.2 dB (A)) and driving to timber piles (90.2 dB (A)).

The performed analyses of the measurement data in the above-described variants of timber forwarding revealed variations in the exposure time of the forwarder operator to noise. In the treatment with the midfield, the authors recorded the shortest forwarding time needed to complete one timber loading (23.28 min.) and a shorter exposure of the operator to noise calculated per 1 m³ of forwarded timber. In the variant without the midfield, the skidding time amounted to 25.80 min. of which the driving time was 4.79 min. In addition, the time analysis of labour operations showed that the noise of the higher sound level (during driving) was shorter in the treatment with the midfield (3.10 min.).

Key words: noise, timber forwarding, forwarder.

INTRODUCTION

Timber harvesting and forwarding represent a dangerous area of forest works. The progress in mechanisation of these works diminish considerably the involvement of physical work and reduce health and life hazards of forest workers. This has become possible because workers can work now at a greater distance from the processed material controlling machines from the safety of the cabin. Many forest machines produced at the present time are characterised by good labour conditions. This is particularly true about harvesters and forwarders, as their modern constructions allow significant reductions of both noise and vibrations exasperating for both operators [1, 2, 3] and natural environment [4]. In addition, well-designed cabins have all their controls placed ergonomically. Nevertheless, there are still manufacturers who continue to produce new machines which do not present full advantage of the latest ergonomic achievements as exemplified by machines emitting acoustic pressures exceeding acceptable standards, e.g. chainsaws and some forwarders [5].

Noise is defined as all undesirable, unpleasant and uncomfortable or harmful vibrations of the elastic medium affecting, by means of the air, the hearing organ and other senses as well as other elements of the human organism [6]. The harmful effect of noise on the human hearing organ depends on the level of acoustic pressure, noise spectrum and duration of exposure. The negative impact of harmful sounds on the human ear occurs when the level of sound exceeds 75-80 dB(A). When the level of the acoustic pressure exceeds 130 dB(A), then even a short-time exposure to it can result in a hearing defect [7]. Longer exposure to noise can result in a reversible and later irreversible overload in the form of hearing defect (Tab. 1), disease of the nervous system, deterioration of work safety and efficiency as well as the overall work comfort and rest. Human hearing is especially exposed to the harmful effect of medium and high noise frequencies [7].

The equipment employed to harvest timber in Poland frequently emits noise which exceeds acceptable standards [5, 14, 15]. Recent progress in the design and corrective ergonomics improved considerably the safety and reduced the irksomeness of new machines [1, 2; 3]. However, this does not refer to all new machines and, that is why, it is important to continue investigations in the area of noise emissions.

The objective of this study was to determine the intensity of noise inside the operator’s cabin of the Vimek 606 6WD forwarder during work activities covering the work with the crane and driving and to determine the time structure of these activities.

RESEARCH SCOPE AND METHODS

Investigations were carried out in the Wierzchucino Forest Range, compartment 195a (Choczewo Forest District, Gdańsk Regional Directorate of State Forests) in a 44-year old pure pine stand of 5.98 ha area. The stand was characterised by full closure, 1.0 stocking and 1a stand quality with no shrub layer.

The studies were conducted in May 2003, in sunny weather during the day work shift. In the area of the above-mentioned forest range, a late thinning operation of 24 m³ ha^-1 intensity was performed using, for this purpose, a Timberjack 770 harvester <footnote 2> (in the midfield, outside the range of the crane of the harvester, thinning was also carried out using a Husqvarna 346 XP chainsaw <footnote 3>). Timber assortments 1.85 and 2.40 m long were cut and placed along the strip roads.

The thinning was carried out in two variants:

1. with a midfield (WMF) – where the distances between forwarding roads exceeded twice the range of the harvester crane (about 35 m), the machine moved along marked strip roads,

2. with strip roads (WSR) – where the distance of strip roads did not exceed twice the range of the harvester crane (about 20 m), the machine moved along marked strip roads.

The obtained timber was forwarded with a Vimek 606 6WD forwarder (manufactured in 1999) of approximately 3.0 m³ timber capacity (Fig. 1). The forwarder was equipped with a three-cylinder Kubota D722-E 20 hp engine of 14.6 kW power (at 3600 rpm), which had worked for 8314 mth. In addition, the machine was equipped with a crane, type 362, of 3.5 m range with a gripping device of 0.15 m² cross-section. During the crane operation, the engine worked at about 1200 rpm., whereas during driving – about 1400 rpm.

The cabin of the forwarder provided sufficient space for the operator to move about relatively freely on his rotating seat. The width of the cabin (from window to window on the level of shoulders) was 106 cm, its height (from the floor to the ceiling in front of the seat) – 155 cm and its length (from window to window on the level of elbows) – 132 cm. The cabin had large areas of glass side walls and a metal roof. The engine was situated in the front part of the machine and was separated from the cabin by a special wall.

The forwarder moved along strip roads. In the case of the WMF method, the harvested timber, which was placed close to strip roads, derived from trees cut with the chainsaw from the area of the midfield (MF) as well as from the area within the reach of the crane of the harvester. Trees cut with the chainsaw on the MF were next de-branched, cut and placed by the harvester.

Six full loads of timber were forwarded from individual test plots obtaining 17.25 m³ of wood from the MF plot and 17.75 m³ from the SR plot.

Throughout the duration of the forwarding work, a chronometer was used to record continuously the time of the following individual activities: loading and driving. During the above-mentioned activities, the level of noise in the operator's closed cabin was measured. In addition, the level of the background noise was determined which amounted to 40 dB(A). All the measurements and assessment of the levels of noise were conducted in accordance with the following standards: PN-81/N-01306 "Noise. Methods of measurement. General requirements" and PN-N-01307: 1994 "Noise. Acceptable values of noise at the workplace". Measurements were performed with the assistance of the Bruel & Kjaer integrating meter of the sound level, type 2231 with a microphone, type 4155 (a set characterised by the first class of accuracy). The employed set had the current certificate of legalisation issued by the President of the Main Office of Measures in Warsaw. The sound level was measured as equivalent values at 1.5 minutes time intervals and setting the meter at 'slow'. Throughout the measurement, the microphone of the sonometer was placed 0.1 meter from the ear of the operator (Fig. 2).

The analysis of the noise emissions in the operator's closed cabin was based on measurements carried out nine times for each activity. The obtained results were analysed statistically subjecting them to the normal distribution test and later to variance uniformity. Statistically significant differences were analysed employing the Tukey test [8].

RESULTS

The Vimek 606 6WD forwarder showed two levels of noise emission in the closed cabin of its operator. The mean level of noise during driving amounted to 90.2dB(A) and was considerably higher in comparison with the level of sound emitted during the crane work: 85.2 dB(A) (Tab. 2).

The performed statistical calculations revealed that the obtained values of the noise level were characterised by normal distribution and their variations were uniform. The performed analysis with the assistance of the Tukey test allowed determining significant differences in the noise level (during the work of the crane and driving) at the level of p <0.05 (Tab. 3).

Further statistical analysis failed to show significant differences in loading times (work only with the crane, without drive-ups). In the case of the WMF plot, the average of 20.18 minutes was used to prepare one full load, whereas on the WSR plot, 21.01 minutes were needed to do the same job.

In the case of the WMF plot, the mean time of drive-ups (from pile to pile) was by 35% shorter than the time needed to carry out the same operations on the WSR plot. These differences are statistically significant with p< 0.05 (Tab. 5).

Further analysis of timber forwarding showed differences in the number of drive-ups of the Vimek 606 6WD forwarder. In the case of the WMF area, fewer numbers of drive-ups were necessary to prepare the whole full load – on average 14 drive-ups, while on the plot with the strip road, it was necessary to make, on average, 20 drive-ups from pile to pile (Tab. 4). These differences turned out to be statistically significant with p<0.05 and confirmed by the Tukey test (Tab. 6).

The analysed elements of the timber forwarding time showed that the time necessary to carry out one complete load did not differ statistically significantly between the discussed variants. The elements which differentiated the analysed forwarding methods referred to the time of drive-ups – shorter in the variant with the midfield and the smaller number of drive-ups – also in the variant with midfields.

DISCUSSION

Investigations on timber harvesting and forwarding in the variant with the midfield are often compared with studies in which machine technology employing strip roads is used [11. 12. 13. 14]. The authors of those experiments analysed the timber harvesting efficiency and unit costs. The technological variant with the midfield proposed in German conditions yielded poor economical results, although higher efficiency was achieved, especially of timber forwarding. The ergonomic analysis of the process with the midfield was carried out, among others, by Giefing et al. and Grzywiński [14. 15]. The authors analysed harvesting processes as a whole without detailed analyses of the labour structure from the ergonomic standpoint. In general, they concluded that the variant with the midfield, due to the introduction of the chainsaw to cut trees on the midfield, resulted in the increase of loads with noise and vibrations.

In our studies, it was shown that the Vimek 606 6WD forwarder emitted levels of noise which can pose a threat to the hearing of the operator. These results are different from those found in the available literature. According to the Forest Research, the noise level in the cabin of the Vimek 606 6WD forwarder <footnote 4> is at the level of 76 dB, but this data does not indicate what type of engine work this value concerns [16]. In our investigations, we recorded higher values of the A sound in the cabin. On average, it reached 85 dB(A) during the work with crane and exceeded 90 dB(A), when the machine was moving. The level of noise exceeding 80 dB(A) should be considered as harmful to the hearing organ [6]. It is, therefore, recommended that the operator should wear ear protectors to prevent hearing defects.

The measurement of noise in the operator’s cabin of the harvester showed a considerable difference between the sound intensity during the work of the crane and during driving, which amounted to 5 dB.

The investigations of the forwarding of timber harvested according to two technologies: with the midfield (WMF) and with the strip road (WSR) showed that the drive-up time was shorter on the WMF plot. This means that, in this technology, the operator of the forwarder was exposed to a higher level of sound (90.2 dB(a)) for a shorter period of time (Fig. 3).

The authors of this study also noticed that the operators working in cabins do not use hearing protectors. In this situation, the operator working in the technology with the midfield was exposed to a more harmful effect of noise (of higher intensity 90.2 dB(A)) during the time by 35% shorter that in the technology with the strip road variant (comparing the times of drive-ups). The shorter time of drive-ups is the resultant of the technology with the midfield – as confirmed by two factors.

The density of strip roads on the WMF plot was by 46 % smaller in comparison with the technology WSR [10]. A thinner network of strip roads results in their smaller current length and shorter time of machine moving on the entire plot which are accompanied by a higher sound intensity (90.2 dB(A)). Another result of greater distances between routes is a considerable accumulation of timber raw material in individual piles which were formed from the timber derived from a greater area. This was the cause of yet another difference observed during forwarding on the WMF plot – the number of drive-ups (between timber piles) was by about 30% smaller.

Timber forwarding using the Vimek 606 6WD forwarder on the plot with the midfield loaded the operator of the machine with less noise. However, bearing in mind the level of noise during driving which exceeded 90 dB(A), it is essential to wear hearing protectors to prevent damage of the hearing.

CONCLUSIONS

1. The level of noise in the closed cabin of the Vimek 606 6WD forwarder on the test plot with the midfield reached 85.2 dB(A) during work with the crane and 90.2 dB(A) – during driving of the machine.

2. The forwarding of timber on the plot with the midfield loaded the operator of the examined machine with noise to a lesser degree. The time of drive-ups, which were accompanied by the highest sound intensity (90.2 dB(A)), was in this technology by 35% shorter. In addition, the number of drive-ups necessary to form one load on the trailer of the forwarder was by about 30% smaller on the plot with the midfield.

3. The time of work with the crane in the course of the load formation did not differ statistically significantly between the examined technologies.

4. The operator of the forwarder was exposed to the harmful influence of noise and should wear ear protectors.

ACKNOWLEDGEMENT

This research project was realised during 2003 – 2005 with the support of funds obtained from the State Committee for Scientific Research (Ministry of Science and Information Society Technologies).

Footnotes

< footnote 1>
In the technology with the midfield, when the strip roads were spaced at the distance of about 35 m, workers – when cutting trees with chainsaws on the area which was outside the reach of the crane (midfield) – fell them towards the strip road which is closer. The harvester acts as a processor for these trees (de-branching, cutting to lengths). This method allows increasing distances between strip roads and limits the penetration of the stand by the harvester and forwarder.

<footnote 2>
The Timberjack harvester 770 was equipped in a Cummins 4BTA 3,9-C110 engine of 82 kW power (2000 rpm.), a Timberjack 140 H crane of 9.2 m length, 732B head which allowed cutting trees up to 350 mm in diameter.

<footnote 3>
The Husqvarna 346 XP chainsaw of 2.5 kW power and the stroke capacity of 45 cm³.

<footnote 4>
The forwarder was equipped with the Kubota D722-E 19,6 hp engine.

REFERENCES

1. Sowa J. M., Leszczyński K. 1999. Akustyczne narażenie kierowcy cišgnika LKT 81 Turbo i operatora harwestera Timberjack 1270B [Acoustic risk of LKT 81 Turbo skidder operator and Timberjack 1270B harvester operator]. Zast. Erg. 2-3: 135-146 [in Polish with English abstract].

2. Sowa J. M., Leszczyński K. 2001. Ocena œrodowiska akustycznego harwestera Timberjack 1270B [Analysis of acoustic environment of harvester Timberjack 1270B]. Pr. Kom. Nauk Rol. PAU 3: 113-119 [in Polish with English abstract].

3. Sowa J. M., Leszczyński K. 2001. Obcišżenie akustyczne operatora nasiębiernego cišgnika zrywkowego firmy Timberjack typu 1010 [Noise risk of Timberjack 1010 forwarder operator]. In: Ergonomia i ochrona pracy w drzewnictwie, leœnictwie i produkcji rolniczej. AR, Poznań – Puszczykowo, 40 [in Polish].

4. Sowa J. M., Leszczyński K. 1999. Oddziaływanie fali akustycznej wytwarzanej przez maszyny stosowane w procesie pozyskania drewna na œrodowisko zewnętrzne. [Influence of acoustic wave caused by timber harvesting machines on the surrounding environment]. Zast. Erg. 2-3: 147-157 [in Polish with English abstract].

5. Mederski P. S. 2004. Ekonomiczne i ergonomiczne aspekty pozyskiwania sosny z zastosowaniem zmechanizowanych procesów technologicznych [Economic and ergonomic aspects of pine harvesting using mechanised timber harvesting operation]. Ph. D. Project, Department of Forest Utilisation, August Cieszkowski Agricultural University of Poznań, Poland [in Polish with English abstract].

6. Augustyńska D., Engel Z. 1997. Hałas [Noise]. In: D. Koradecka (ed.). Bezpieczeństwo pracy i ergonomia [Work safety and ergonomics], 373-401. CIOP, Warszawa [in Polish].

7. Roczniak M. 1996. Fizyka hałasu [Physics of noise]. Politechnika Œlšska, Gliwice [in Polish].

8. Stanisz A. 1998. Przystępny kurs statystyki [Accessible course of statistics]. StatSoft Polska, Kraków [in Polish].

9. ISO 1999: 1975 (first edition), 1990 (second edition) Acoustics – Determination of occupational noise exposure and estimation of noise – induced hearing impairment.

10. Mederski P.S. 2004. Selected economic aspects of mechanised pine harvesting and the density of skid roads in the forest environment. Abstract in: Transformation to Continuous Cover Forestry in a Changing Environment. University of Wales, Bangor, 53.

11. Bacher M. 2003. A mechanized harvesting system for large-sized wood in permanent stands. 2^nd Forest Engineering Conference, Vaxjo, Sweden:13-21.

12. Bort U., Mahler G., Pfeil Chr. 1993. Mechanisierte Holzernte. Wechselwirkungen von Ershließungsdichte, Pflegliechkeit und Betriebserfolg [Mechanised timber harvesting. Analysis in dependence on forest access, tending intervention and company ability]. Forsttech. Inf., 11: 121-124 [in German].

13. Forbrig A., Dummel K., Gehringer M. 1996. Die Verfahren der Fachexkursion bei der 12. KWF-Tagung 1996. Durchfostung mit Kranvollernter bei 40m Rückegassenabstand [Professional excursion during 12^th KWF Conference. Thinning with use of harvester on skid roads with distance 40 m between them]. AFZ-Der Wald, 8: 451-454 [in German].

14. Giefing D. F., Hołota R., Gackowski M., Karaszewski Z., Klentak I., Kosak J., Bembenek M., Siewert S., 2000. Badania zmierzajšce do opracowania optymalnych technologii pozyskiwania drewna w przedrębnych drzewostanach iglastych [Research in order to obtain best thinning operation for coniferous stands]. In: Dokumentacja – Generalna Dyrekcja Lasów Państwowych, Warszawa, pp. 141 [in Polish].

15. Grzywiński W. 2003. Wpływ zastosowanej techniki i technologii na poziom humanizacji pracy w leœnictwie [The influence of the applied technique and technology on the level of work humanisation in forestry]. Ph. D. Project, Department of Forest Utilisation, August Cieszkowski Agricultural University of Poznań, Poland [in Polish].

16. Forest Research. 2000. The Vimek 606D mini-forwarder. Information note ODW 7.12a. www.forestry.gov.uk.

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