1. Introduction
The introduction of fully mechanized wood harvesting is unfeasible in several countries, at least for now, due to steep terrain, fragmentation of ownership, and environmentally-friendly forest management practices (close-to-nature management). As a result, motor-manual harvesting remains the dominant method of wood harvesting for many countries (Southeastern Europe, Asia, Asia Africa) [
1,
2,
3,
4]. The advantages of chainsaw use include low investment cost and the flexibility of its use, as it is the only motorized tool allowed to be used within the forest [
5,
6,
7]. Additionally, gasoline-powered chainsaws have seen a slow but steady increase in their performance by increasing engine power and speed control [
8]. This means that higher performance contributes to a reduction in energy consumption for the production of one unit of goods. According to [
9], increased productivity reduces greenhouse gas emissions, which are the main cause of climate change.
However, chainsaw use has its drawbacks, including noise, vibrations, physical strain, exhaust gases, and airborne wood dust [
10]. Several researchers have examined the problems associated with noise [
11,
12,
13], vibrations [
14,
15,
16], physical strain [
17,
18,
19], as well as the determination of carbon monoxide [
20,
21], and exhaust emissions [
22,
23,
24].
Regarding the concentration of airborne wood dust in real working conditions during harvesting in a forest, fewer researchers have focused on this topic [
25,
26], while there is sufficient research on wood dust concentrations in enclosed spaces such as wood industries [
27,
28,
29]. However, several researchers emphasize that the occupational exposure limits are based on epidemiological studies from the furniture industry and may not reflect the specific conditions prevailing in outdoor workspaces.
Usually, chainsaw operators do not take into consideration the risk of exposure to airborne wood dust, as they are less aware of its negative health consequences [
30]. Nevertheless, the risk is significant, such as the changes it can induce in pulmonary function and allergic respiratory responses (asthma). Moreover, there is a scalable risk of developing cancer, particularly nasal and sinus adenocarcinoma [
31,
32]. For this reason, the International Agency for Research on Cancer has classified hardwood dust as carcinogenic [
33]. Therefore, there is a relevant directive [
34] for the countries of the European Union, which sets the legal exposure limit for inhalable wood dust at 5 mg/m
3 [
25]. Meanwhile, there is a continuous trend of reducing this limit. In 2017, with [
35], the occupational exposure limit (OEL) was reduced to 3 mg/m
3 until January 17, 2023, and later to 2 mg/m
3.
The chain is one of the essential parts of a chainsaw, and the correct selection of the chain affects important factors such as cutting efficiency, safety, and ergonomic suitability of the chainsaw [
8]. However, it is observed that while there is technical data available for the correct selection of a chainsaw chain in relation to the chainsaw, there is a lack of quality data for making rational decisions in choosing a chainsaw chain [
8]. A literature review revealed the need for a new comprehensive analysis of the risks associated with the use of internal combustion portable chainsaws [
36]. [
8] emphasize that assessing the effectiveness of the most relevant technical solutions used today in portable chainsaws to protect operators' health from inhaled dust during work is of great importance.
The objective of this study was to determine the factors that affect the performance and concentration of inhalable wood dust produced using chains of different pitches. In chainsaws, the chain pitch refers to the distance between three consecutive rivets divided by two (
Figure 1). It is a measurement that determines the compatibility between the chain and the guide bar on the chainsaw. The chain pitch represents the size of the chain, specifically the spacing between the drive links that engage with the sprocket and guide bar, and it is usually measured in inches. The correct chain pitch must match the corresponding sprocket and guide bar to ensure proper functioning and optimal cutting performance of the chainsaw. Chains with different pitches are not compatible with one another, as their drive links will not align or engage correctly with the sprocket and guide bar. A typical chainsaw chain has a pitch of 3/8" (9.5 mm) [
37]. Specifically, the study considered: (i) two types of chains with different pitches from the same producer, (ii) three tree species, and (iii) healthy standing and dead trees. It should be noted that this research effort is part three of a larger research project, with part two focusing on the operating conditions of chainsaws in terms of maintenance [
38], and part one on tree dimensions and tree species [
39].
4. Discussion
Exposure to wood dust poses respiratory and dermatological risks, including potential carcinogenic effects [
45]. Unfortunately, workers often lack awareness regarding the hazards of occupational wood dust exposure, potentially due to adaptation to working conditions and a lack of specific government standards [
46]. Current occupational exposure limits for wood dust are based on the wood processing industry and apply to an 8-hour workday without specifically addressing the forestry and logging sector. Furthermore, there is a lack of standardized procedures for measuring wood dust concentration from chainsaws [
10].
To address these issues, this study conducted measurements of inhalable wood dust during real harvesting operations within the breathing zone of chainsaw operators. The research aimed to assess the influence of chain pitch, tree species, and the presence of dead standing trees (caused by fire) on airborne wood dust concentrations in timberland. The results show a slight variation in wood dust generation influenced by chain pitch, with mean concentrations of 3.07 mg/m
3 for a 3/8" chain pitch and 2.82 mg/m
3 for a 0.325" chain pitch during a 6-hour work duration (
Table 4). Moreover, the sampling indicated a higher percentage (12.50%) of very high wood dust concentrations (>5 mg/m
3) associated with the 3/8" chain pitch.
Figure 4 also illustrates that, excluding beech, all other tree species exhibited higher wood dust concentrations with the 3/8" chain pitch. These findings correspond with the work conducted by [
47] highlighting risks and increased inhalable dust concentrations during salvage cut operations on dry wood left in the forest for an extended period.
Similar studies conducted by [
48,
49,
50] measured wood dust concentrations during the cutting and processing of dead standing trees. They found higher mean concentrations of total wood dust mass and inhalable fractions for oak wood, followed by fir and beech wood [
48,
49,
50]. Additionally, [
25] evaluated inhalable wood dust exposure in various forest operations, indicating higher mean wood dust concentrations in clear-cut coppice operations compared to silvicultural treatments, particularly focusing on hardwood species (
Quercus cerris L.,
Ostrya carpinifolia L.).
Table 5 demonstrates an association between wood dust concentration classes (>5 mg/m
3, (3,5] mg/m
3, and ≤ 3 mg/m
3) and mean breast height diameter, with smaller diameters (34.72 cm) corresponding to the very high concentration class. The diameter tends to increase as wood dust concentration decreases, reaching 38.34 cm for the high concentration class and 40.01 cm for the acceptable concentration class. These findings are consistent with previous research highlighting the inverse relationship between wood dust concentration and tree dimensions [
39].
Furthermore,
Table 2 and
Table 3 indicate that wood dust concentrations are not influenced by the chainsaw operator's work rate, as consistent work rates were maintained throughout the sampling period, ensuring reliable and accurate results.
5. Conclusions
The safety improvements offered by fully mechanized harvesting operations do not apply to motor-manual harvesting work [
51,
52]. Considering that in many countries (Southeastern Europe, Asia, Asia Africa) the chainsaw is the only logging machine used in the forest [
1,
2,
3,
4], it is necessary to continuously improve chainsaws to make the work as human-friendly as possible [
8]. Due to limited data on wood dust exposure and the lack of clear standards [
46] for protecting workers from wood dust exposure, there is significant uncertainty in assessing the risks faced by forest workers.
In this study, it was found that approximately 44% (42 out of 96 sampling filters) of the total sampling filters exceeded the occupational exposure limit that applies to wood dust in most European countries (3 mg/m
3). Furthermore, it was found that the chain pitch affects wood dust levels. Specifically, using a 0.325" chain pitch compared to a 3/8" chain pitch resulted in lower wood dust concentrations overall and for each tree species, except for beech, where there was a small difference that was not statistically significant. Increased wood dust concentrations were observed in tree species with thick bark, such as oak and pine, while the lowest wood dust concentration was observed in beech, which has a relatively high wood density but thin bark. These findings align with a previous study by [
26], which allows us to conclude that bark thickness primarily influences wood dust levels. Additionally, an additional conclusion from this research is that the highest wood dust concentrations were found in dead standing Pinus trees.
Taking into account the unique and specialized extracts found in each tree species, the toxicity of fresh wood differs. In this context, pine contains endotoxins and monoterpenes, which make the generated wood dust more hazardous [
53,
54]. Therefore, it is not only the quantitative characteristics but also the quality characteristics of fresh wood dust that make it dangerous for workers. In this regard, the existing occupational exposure limits for wood dust should be reconsidered, especially for the forestry sector.
Based on the conclusions of this study, and considering that the chain is one of the essential parts of a chainsaw, it is evident that the type of chain directly affects both work efficiency and the risk to workers' health. While chainsaw manufacturers typically advertise safety features, it is clear that producers need to make complex decisions to optimize chains so that safety goals can be achieved. Nevertheless, more research is needed on the quality characteristics of a chain, rather than just the technical characteristics, to facilitate better and more transparent information about the choice of a chain [
8].