The introduction of mechanized harvesting has been hindered by several factors, including steep terrain, ownership fragmentation and close-to-nature management [1
]. Motor-manual tree felling and processing using a chainsaw therefore remains the predominant harvesting method in many regions of the world (South East Europe, Asia, Africa) [2
]. Additionally, the low investment cost and the chainsaw’s versatility play a significant role when harvesting technology is chosen in private forests [5
]. The chainsaw’s simplicity and inherent reliability make it ideally suited for the harsh working conditions commonly encountered in forest operations.
Petrol chainsaws have recently witnessed a steady, but slow increase in cutting efficiency related to increases in engine power and speed, and improvements in the control of engine performance. Higher efficiency reduces the amount of time and energy required for the production of one unit of goods. Therefore, increased productivity reduces greenhouse gas emissions, which are considered to be the main cause of climate change [8
Unfortunately, motor-manual forest work is inherently dangerous [9
], physically demanding [11
] and involves physical environmental factors which have an extremely detrimental effect on worker health. Workers engaged in motor-manual cutting are exposed to excessive noise and vibration [13
] and to the effects of exhaust gases [16
], floating particles of mineral oil and airborne wood dust [17
Although the air in logging operations can be very polluted [20
], very few motor-manual workers are aware of the negative consequences of exposure to dust. The risk, however, is significant, and the International Agency for Research on Cancer has classified hardwood dust as a human carcinogen [21
]. It is estimated that in 25 member states of the European Union, 2% of the work force is occupationally exposed to inhalable wood dust [22
]. In the European Union the Directive 99/38/EC [18
], is setting the legal limit for the exposure to inhalable wood dust at 5 mg/m3
, as an average of an 8-h working day. In regard to the size of particles inhalable, thoracic and respirable particles are to be distinguished [23
]. In our study however, as a health risk indicator, the share of the inhalable wood dust in regard to the total amount of saw dust was used [24
Potential health effects from exposure to wood dust are numerous and well documented [25
] and include changes in pulmonary function and allergic respiratory response (asthma). The most serious problem arising from exposure to wood dust is the risk of developing cancer, particularly nose and sinus adenocarcinoma [26
The saw chain, as the main sawing part, influences the efficiency, safety and ergonomic suitability of the chainsaw. The main problem for the user is that only the technical data that are needed for compliance of the chain with the saw bar are available for any single chain. There is no, or insufficient, qualitative data needed for rational decision making. Producer information about quality, i.e., “chain with lower vibration,” is more a function of faith in a trademark than of rational thinking. The problem is exacerbated because of the lack of knowledge available about basic principles of how efficiency or health risk change depending on chain maintenance practices.
Practice and science agree that proper filing and maintenance of the saw chain is crucial for safe and efficient work [27
]. The word “proper” usually means that users have followed the producer’s directions. In practice, however, modification of filing direction and depth is common, with implications for chain durability and work efficiency.
Since the cutting chain is one of the most important parts of the chainsaw, its preparation and maintenance have a direct impact on work efficiency and health risk. The aim of the study was therefore to determine the factors affecting efficiency and the amount of inhalable wood dust produced during cross cutting with a chain saw. To achieve these goals, the experiment has been set up including two filing factors, two tree species and two saw chains from different producers. The effect of wood moisture was controlled, as it has been established that it affects particle size distribution [28
According to our experience and previous studies, it was expected that the chain setting recommended by the producer would yield the greatest efficiency and the lowest health impact, as the indicated values are presumably the result of in-depth analysis performed by the chain producer. The chains were chosen from two established producers, and tree species were chosen according to their predominance in Central Europe, although no specific hypotheses were proposed based on these factors.
2. Materials and Methods
The experiment was designed as a full factorial design (Table 1
) with two factors at two levels and two factors at three levels (22
). To eliminate the possible effect of wood structure and moisture, each combination was repeated five times (Scheme 1
). The positive effect of repetition of cross cutting on experimental design was confirmed with an insignificant difference in wood moisture between all factors involved in the experiment with the exception of tree species. The average wood moisture was 32.9% for fir (Abies alba
Mill.) and 50.6% for beech (Fagus sylvatica
L.). The total number of crosscuts with repetitions was 180 or 10 by each saw chain setup. For the purpose of wood dust analyses, additional crosscuts (11th and 12th crosscut, Scheme 1
) were done at all factorial levels but without repetitions (n = 36).
In the trial, air dried, two first class logs of fir and beech were used. The logs were standardized into a beam with length of 6 meters and sides of 32 × 32 cm, in compliance with ISO standards [29
]. The beams were cut into 6 shorter (about 2 m long) sections just before the trial (Scheme 1
A new Husqvarna 372 XP professional chain saw with a 45-cm-long Stihl Rollomatic E cutting bar was used in the experiment, and a skilled worker was employed as the chain saw operator. Eighteen 3/8′′ chisel chains with 72 drive links from two different producers were used and filed in accordance with the trial scheme (Table 1
). The top filing angles recommended by the chain producers differ for 5°. The top plate filing angle was done using a Stihl USG filing tool, while correct depth gauge height was achieved using hand filing and controlled with calipers.
Cross cutting took place in turns according to tree species and always in the same sequence (Scheme 1
). The sequence of used chain setups was randomly selected. To further guarantee comparable conditions, cutting chain tension was controlled and the weight of the saw was kept at the same level by assuring the same level of lubricant and gasoline in the saw. The saw was controlled only through the rear handle, assuring that the pressure applied to all sample logs was constant. Visible defects in the wood were avoided when cross cutting.
The whole trial was recorded using a camera (Sony HDR-XR200; Sony, Tokyo, Japan), while the time studies were performed in the office to ensure the highest precision of measurement. A total amount of saw dust was directly captured in a plastic bag using an adapter attached to the chain saw. Moisture content was determined with the gravimetric method, according to European standards [30
]. Fresh sample weight was determined immediately after sample collection with a portable scale to avoid the bias caused by moisture loss during storage and transport to the laboratory. Particle size distribution was determined with the oscillating screen method according to European standards [31
]. Entire samples were sieved, and from the mass of fractions the shares of particle size distributions were calculated. The share of fine particles from the particle size distribution analysis was used as an indicator value.
Parametric multivariate analysis of variance (MANOVA), univariate analysis of variance (ANOVA) and ordinary least squares regression were used for statistical data processing. Before analysis, dependent variables were checked for normality (Kolmogorov–Smirnov and Shapiro–Wilks tests) and homogeneity of variance (Levene’s test). In case of violation of data considerations, variables were transformed.
For the analysis of cross cutting duration, all samples were used (n = 180). To meet considerations for use of parametric tests (MANOVA, ANOVA), the dependent variable (time) was transformed with the inverse square root transformation.
Because of the interdependent nature of particle size distributions, basic approaches of compositional data analysis were used [28
]. Compositional data were transformed using Isometric Log Ratio transformation in the CoDaPac software (2.02.04, 2017, University of Girona, Girona, Spain) [32
]. The data were analyzed with IBM SPSS Statistics software (21.0, 2012, IBM, Armonk, NY, USA).
The results show that the work efficiency and health risk due to inhalable dust is influenced by all of the researched factors: chain filing, tree species and chain producer. Ignorance of the above factors can result in significant differences in work efficiency and increased health risk.
From the viewpoint of efficiency and dust particles, the best top plate filing angle was the angle recommended by the chain producer. With this angle the cross cutting time and the amount of inhalable dust particles reached a minimum. These results are in direct contradiction with research that found that the top plate filing angle recommended by the producer corresponded to the greatest exposure to hand-arm vibration [33
]. However, it was established that from the viewpoint of efficiency, it is better that the top plate filing angle is smaller than the angle recommended by producer rather than larger. The real-world implications of these findings are that mistakes made by less-experienced chain saw operators depend on the deviation from the recommended angle, and it is not as critical when the angle is smaller than that prescribed.
The depth gauge height has been found to deviate strongly in real-world operations, as only 15% of chains were found to have the proper gauge depths [34
]. The consequence of large depth gauge height is higher cutting efficiency, while no statistically significant effect has been found on the quantity of hazardous dust particles. Excessive depth gauge heights are not recommended, as they lead to higher levels of kickback forces [35
] and larger vibration loads [36
]. Higher depth gauge setting increases the chain saw power requirements, and the consequences are higher fuel consumption, higher weight, higher vibration exposure and potentially greater negative impact on the health of the environment and worker. The open question remains the optimal relation between depth gauge setting and all of the above factors.
The effect of different wood species is important because of different wood density, as it was established that wood density has a significant effect on hand-arm vibration exposure [15
]. The influence of the user on this factor is relatively small, as this factor depends on the worksite. However, a detailed analysis of interactions between factors has shown that the species influences cutting efficiency through the factors of top plate filing angle and saw chain producer. The dependency was confirmed by the experience of cutters, who often alter chain angles depending on whether the work is in hardwood or softwood forests. Another possible cause for differences in work efficiency and health risk is the wood moisture content, which is significant between tree species.
Few studies have examined exposure of forest operators to wood dust, but it was determined that exposure to dust was 1.5 mg/m3
for all operations except coppicing, where loads were greater [18
]. Most loads, however, were lower than the EU occupational exposure limit (OEL) of 5 mg/m3
. This level has been disputed, as some countries have lower allowed OEL levels, and the figures reported in the above study are above the allowed levels in some EU countries. In the article it has been shown that the amount of inhalable dust particles can be effectively lowered with the use of different filing angles. Also, salvage cuts of trees that have remained in the forest long enough for the wood to become dry should be avoided, as such trees are associated with a higher risk of accidents [10
] and the risk of high concentrations of inhalable dust particles [37
]. Additionally, the cutting chain preparation in the studies is usually not controlled, but it has been demonstrated that it is indeed a very important factor when conducting sawdust analysis, as it influences sawdust composition and therefore the amount of inhalable dust produced. The measured quantities of inhalable wood dust are to be considered as potential risk for health, since it is assumed that only part of inhalable saw dust enters the air and a part of that dust enters the worker’s body.
One of the main conclusions is that producers do not produce equivalent chains. The chain type therefore influences the cutting efficiency and the health risk for the chain saw operator. Furthermore, after a number of cuts the performance and risk for health [15
] may change because of different durability of chains. The results clearly demonstrate that a rational decision when purchasing a saw chain is crucial, and force producers into continued technological development.
It has to be acknowledged that in the study only two factors were taken into consideration from the pool of factors that influence the suitability of a saw chain for professional use. For instance, the viewpoint of safety at work in the sense of vibration exposure has not been included, and protection against kickback. It is assumed that the producer carefully weighs all of the above considerations when designing the product, and chooses the optimum accordingly. The results, however, show that it would be reasonable to provide not only one filing angle, but several, or to develop chains specifically intended for conifers or broadleaves.
From the lessons learned, the extension of scope in similar future studies is suggested, especially the inclusion of additional parameters, such as fuel and lubricant consumption, hand-arm vibration, different wood moisture levels, different lengths of cutters, direct measurements of airborne wood dust emissions and durability and life span of saw chain. Also, there are other, smaller chain saws, i.e., non-professional and electric chainsaws that use smaller chains and that could significantly alter the results. It has been found that the wood species also influences kickback forces [35
], and an important safety consideration is how the filing angle influences the kickback of the saw in relation to wood species. Certainly, it would have the highest value for practice by testing different chains, their lifespan and their properties in real-life conditions during forest operations.
Unfortunately, the safety improvements offered by high mechanization are unattainable for motor-manual work [38
]. It is therefore necessary to continually improve machines to make work as friendly to the worker as possible. Although all of the saw chain producers advertise safety features, and it is clear that it is necessary for producers to make complex decisions related to optimization in order to achieve these goals, more work should be done on the topic in order to provide more accessible and transparent information about saw chains.