Abstract
Given the well-known carcinogenicity of hardwood dust, occupational exposure to oak wood dust has been determined in a furniture factory on different wood processing machines during sanding, planing, and milling. Determination of the mass concentrations of respirable and inhalable oak wood dust from ambient air was performed using personal sampling pumps and two types of filter holders: the Higgins-Dewell respirable dust cyclone, manufactured by Casella (Bedford, UK), and the inhalable dust IOM sampler manufactured by SKC (Dorset, UK). Out of a total of 30 values of inhalable mass concentration, 7 (23%) exceeded the occupational exposure level (OEL). The highest exposure levels for inhalable and respirable wood dust from the belt sander were 1.569 to 3.710 mg/m3 and 0.243 to 1.342 mg/m3, respectively. Worker exposure may be below the level of increased risk of 2 mg/m3 if a machine such as a planer or router is connected to a suction system. The share of respirable particles in the inhalable fraction ranged between 12% and 31%, and for samples with an inhalable mass concentration exceeding 2 mg/m3, the share was lower than 16%, with a slightly decreasing tendency. Thus, the risk of lower respiratory tract diseases increases with higher exposure to inhalable particles, and the OEL is an indirect measure of protection against exposure to respirable particles.
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Occupational Exposure to Inhalable and Respirable Wood Dust of Pedunculate Oak (Quercus robur L.) in a Furniture Factory
Anka Ozana Čavlović,a Ivan Bešlić,b Stjepan Pervan,a Nikolina Barlović,a Mislav Mikšik,a Miljenko Klarić,a and Silvana Prekrat a
Given the well-known carcinogenicity of hardwood dust, occupational exposure to oak wood dust has been determined in a furniture factory on different wood processing machines during sanding, planing, and milling. Determination of the mass concentrations of respirable and inhalable oak wood dust from ambient air was performed using personal sampling pumps and two types of filter holders: the Higgins-Dewell respirable dust cyclone, manufactured by Casella (Bedford, UK), and the inhalable dust IOM sampler manufactured by SKC (Dorset, UK). Out of a total of 30 values of inhalable mass concentration, 7 (23%) exceeded the occupational exposure level (OEL). The highest exposure levels for inhalable and respirable wood dust from the belt sander were 1.569 to 3.710 mg/m3 and 0.243 to 1.342 mg/m3, respectively. Worker exposure may be below the level of increased risk of 2 mg/m3 if a machine such as a planer or router is connected to a suction system. The share of respirable particles in the inhalable fraction ranged between 12% and 31%, and for samples with an inhalable mass concentration exceeding 2 mg/m3, the share was lower than 16%, with a slightly decreasing tendency. Thus, the risk of lower respiratory tract diseases increases with higher exposure to inhalable particles, and the OEL is an indirect measure of protection against exposure to respirable particles.
DOI: 10.15376/biores.17.4.5831-5847
Keywords: Hardwood dust; Carcinogenicity; Personal sampling method; Inhalable fraction; Respirable particles; Sanding; Milling; Planing
Contact information: a: Faculty of Forestry University of Zagreb, Wood Technology Department, P.O. Box 422, 10002 Zagreb, Croatia; b: Institute for Medical Research and Occupational Health Zagreb, P.O. Box 291, 10001 Zagreb, Croatia; *Corresponding author: sprekrat@unizg.sumfak.hr
INTRODUCTION
In 1994 the IARC (International Agency for Research of Cancer) classified wood dust into the first group of carcinogenic substances, whereas workers in furniture production exposed to a higher risk of nose and nose cavity cancer were placed into the first risk group. Cancer is the first cause of work related deaths in the EU, and 53% of all occupational deaths are attributed to cancer. An average 2% of workers from over 179 million in the EU25 Member States are exposed to inhalable wood dust, amounting to 3.6 million workers (Kauppinen et al. 2006). European Directive 2017/2398 on the protection of workers from the risks related to exposure to carcinogens or mutagens at work prescribes an OEL of 2 mg/m3 (3 mg/m3 until 17 January 2023), which refers to a mass concentration of increased risk.
One of the first reports of occupational risk associated with hardwood dust exposure came from England in 1967, indicating an excessive risk of nasal cavity and sinus adenocarcinoma among woodworkers in the furniture industry (Acheson et al. 1968). A study of the impact of exposure to wood dust on occupational health and its implications on the occupational limit value showed that workers exposed to inhalation dust at levels of 2 mg/m3 and above have no adverse effects on the lungs (Holm and Festa 2019). In an industry-based case control study in the German woodworking industries, the authors found an elevated risk of adenocarcinoma of the nasal cavity and paranasal sinuses due to exposure to inhalable wood dust above 3.5 mg/m3. The rareness of the disease does not allow the exclusion of risk below that concentration (Pesch et al. 2008). However, the current occupational exposure limit for inhalable wood dust, based on mass, cannot detect a high exposure to ultra-fine particles (UFP), and particles <10 µm that are easily deposited in the smallest parts of the respiratory system (Gu et al. 2018). Woodworkers are estimated to have a 500-fold higher risk of developing sinonasal adenocarcinomas compared to the male population and up to 900 times higher than the general population (Llorente et al. 2009). In addition to the importance of hardwoods, especially beech and oak wood, both hardwood and softwood dusts can influence the development of the inflammatory process in the airways, by modulating the expression of macrophage derived cytokines and chemokines. Although there are some differences in the magnitude of responses to different wood dust species, they have quite similar effects on the cytokine and chemokine expression in the cell line (Määttä et al. 2005, 2006; Bornholdt et al. 2007). Cumulative exposure to even softwood-dominated mixed wood dust is strongly associated with an increased risk of nasal adenocarcinoma, but not with other types of nose or nasopharyngeal cancer (Siew et al. 2017). Intestinal-type sinonasal adenocarcinoma represents from 8% to 25% of all malignant sinonasal cancers and is etiologically related to occupational exposure to wood dust. Some genetic and chromosomal analyses of wood dust exposure have been found to be causative factors in mutagenesis with a specific transient mutation in non-smokers or smokers only (Llorente et al. 2009; Pérez-Escuredo et al. 2012). The estimated relative risk of developing sinonasal epithelial cancer after 35 years of exposure to wood dust is about 300, compared to non-exposed people for whom the relative risk is equal to 1 (Soćko 2021).
The results of the random effects model meta-analysis showed that there was a direct relationship between occupational exposure to a high concentration of wood dust and nasopharyngeal cancer (Beigzadeh et al. 2019; Meng et al. 2020). A strong impact on the risk of laryngeal cancer has been observed for high exposure to hardwood and softwood dust (Ramroth et al. 2008). High exposure to hard-wood and softwood dust contributes to the evidence that wood dust, especially hardwood dust, is an independent risk factor for laryngeal cancer, in addition to the influencing factors of smoking, alcohol, and education levels (Ramroth et al. 2008).
In addition to the fact that wood dust is a known carcinogen that can cause cancer, mainly in the upper respiratory tract, in recent times, exposure to wood dust has been associated with a significantly increased risk of lung cancer and an increased risk of squamous cells, small cells and lung adenocarcinoma, especially in persons who are regularly exposed to wood dust for a long time (Scarabelli et al. 2021). A different study has found that there is no significant association between lung cancer and exposure to wood dust. The risk of lung cancer was slightly increased in those who were professionally exposed to wood dust for more than 10 years, and for whom it was over 40 years since the first exposure (Matrat et al. 2019). Quantitative assessments can prevent diseases associated with exposure to wood dust such as sinonasal and lung cancers (Sauvé et al. 2019).
Occupational exposure to wood dust presents a risk factor for non-malignant respiratory diseases consistent with both an allergic and a non-allergic origin (Schlünssen et al. 2018). Work in the furniture and wood processing sector was associated with a significantly increased risk of respiratory symptoms and asthma (Wiggans et al. 2016). In a longitudinal study of the association between exposure to wood dust and emerging chronic obstructive pulmonary disease (COPD) and changes in lung function, the results suggests that female carpenters may be more sensitive to exposure to wood dust than male woodworkers (Bolund et al. 2018). A Scandinavian study shows that exposure to wood dust in a previous year increases the risk of re-admission to the hospital for people with asthma, but not for those with COPD (Vested et al. 2021). Exposure to wood dust in the workplace is associated with the onset of chronic rhino-sinusitis (Clarhed et al. 2020). The presence of asthma and rhinitis was detected in furniture workers exposed to wood dust, and the most useful tests for diagnosing these occupational diseases were determined (Paraskevaidou et al. 2021).
Exhaust ventilation in joinery and furniture manufacturing has been shown to reduce dust concentrations, while specific tasks and work processes including sanding, use of compressed air for cleaning, use of hand tools or fully automated machines, dry wiping and cleaning, and the reduced size of a workshop may increase wood dust exposure (Kos et al. 2002, 2004a,b; Schlünssen et al. 2018). A study of the long term changes in worker exposure to wood dust in the UK found decreasing trends (Galea et al. 2009). Workers using conventional sanding systems could use self-generated vacuum sanding system technology to potentially reduce particle exposure and mitigate adverse health effects (Liverseed et al. 2013). Sanding, especially hand sanding, nearly always resulted in inhalable exposures above 5 mg/m3 (Scheeper et al. 1995). Wood processing with high levels of inhalable dust can emit a large number of UFPs and particles <10 µm (Gu et al. 2018). Former studies have suggested that sanding with a hand sander is one of the processes that can cause the highest exposure to wood dust. Softwood generated more dust than hardwood due to the difference in abrasion durability of the wood. A coarse sand paper produced more dust than a fine sand paper. When the specimens were sanded with a fine sand paper, the mass median aerodynamic diameters of beech wood dust and cypress wood dust were 9.0 μm and 9.8 μm, respectively. Respirable wood dust is able to be controlled by general ventilation with an air flow rate of over 0.7 to 4.2 m3/min (Ojima 2016). The mass concentration of the smallest dust particles has a negative linear relation to the total air flow rate of the exhaust system during sawing with a circular saw (Palubicki et al. 2020). Woodworking by computer numerical control router (CNC) is often the cause of increased dust in the surrounding air, due to the geometry of the tool, as well as the conditions of its operation. There is no possibility of effective removal of dust particles dispersed in the air during CNC machining, especially as the tool often moves considerably long distances in many directions (Rogoziński et al. 2015). The aim of the present research was to contribute to determining the occupational exposure of workers to oak wood dust in furniture production plants at different wood processing machines. New measurement results of respirable and inhalable mass concentration were obtained. By reviewing the share of respirable dust present within inhalable dust, based on mass concentration, indications were obtained of the influence of oak wood processing on worker’s exposure in the observed conditions.
EXPERIMENTAL
Materials
Determination of wood dust mass concentration by the gravimetric method was carried out at different wood machining places in the furniture factory, during the processing of the dry hardwood species of the pedunculate oak (Quercus robur L.). The workspaces observed, selected as a cross section of specific machines in the furniture factory, were near two types of CNC machines, types PRO (Homag, Schopfloch, Germany) and Double Jet (Paulino Bacci, Cascina, Italy), two types of hand sanders, a random orbital sander (Atlas Copo, Nacka, Sweden) and a belt sander (Makita, Aichi, Japan), and near a four-side planer (Weinig, Tauberbischofsheim, Germany). The working parameters of the machines are presented in Table 1. The belt sander (HS II) has a suction bag attached, but the orbital sander (HS I) does not. The sanding work of HS I is done on a downdraft table connected to the central suction system.
The new type of CNC machine is located separately in a newer production plant, and the other machines observed are located in a production plant with older technology.
Table 1. Working Parameters of Woodworking Machines in the Furniture Factory
Methods
Determination of wood dust mass concentration
Determination of the mass concentrations of respirable and inhalable wood dust from ambient air was performed using personal sampling pumps and two types of filter holders: the Higgins-Dewell respirable dust cyclone manufactured by Casella (Bedford, UK) alongside an inhalable dust IOM sampler, manufactured by SKC (Dorset, UK). Recommendations for wood dust sampling include the convention for measuring airborne particles as specified in EN 481:1993 and CEN /TR 15230:2005. When a mixture of particles of all sizes is inhaled, larger particles settle in the upper part of the respiratory system (inhalable fraction) and smaller particles penetrate deeper into the respiratory tract, through the tracheobronchial zone to the alveoli (respirable fraction). The inhalable fraction is the mass fraction of total floating particles inhaled through the nose and mouth. The respirable or alveolar fraction is the mass fraction of inhaled particles that penetrate into the alveoli.
Ten Casella Apex personal sampling pumps per day were used, set at a suction flow rate of 2 L/min, in determining the mass concentration using an inhalable dust IOM sampler, or set at 2.2 L/min using a respirable dust cyclone sampler. The measuring equipment, a personal sampling pump and filter holder, were worn by the worker over a work-suit. The filter holders are fixed in the worker’s breathing zone. Each equipment pair was used to collect respirable and inhalable wood dust fraction simultaneously during 8 h of work in a full-time shift.
Whatman 25-mm quartz filters (QM-A) were conditioned in the desiccator at 20 ± 1 °C and 47.5 ± 2.5% relative humidity for 48 h before weighing, and before and after the sampling. After the first weighing, the conditioning was repeated under the same conditions for a period of 24 h and the filters are weighed again. Each filter was electrostatically discharged prior to weighing using a Mettler Toledo U-electrode. The weighing was performed using a micro-scale Mettler-Toledo MX-5 (Mettler-Toledo International Inc., Greifensee, Switzerland) with 10-6 g scale sensitivity. Whatman 25-mm quartz filters were used for all measurements. The mass concentration of dust was determined using the gravimetric method in accordance with the standard ZH 1/120.41:1989.
In accordance with CEN/TR 15230, the mass limit of detection (LOD) was calculated as three times the standard deviation of field blanks. The amounts were 0.008 and 0.134 mg for samples collected in the newer production plant, and 0.053 and 0.447 mg for samples collected in the older plant, for the respirable and inhalable mass determination respectively. All sample masses of respirable fraction and inhalable samples collected in the new plant were higher than LOD, but three samples of inhalable dust from the old production plant were below LOD, and they were removed from the calculation.
Statistical differences between the compared results were tested using the Studentˈs test. The Mann-Whitney u-test was used when the condition of homogeneity of variance was not fulfilled. All statistical analyses and graphs were made using STATISTICA 14.0.0.15 (StatSoft Inc., Tulsa, OK, USA).
RESULTS AND DISCUSSION
The geometric mean and range of inhalable mass concentration obtained at different workspaces are presented in Table 2. The geometric mean, as a better indicator of dust emission, was also chosen to show the average value of the mass concentration of wood dust for all groups of samples. All measured values are compared with the European OEL, in accordance with the prescribed value of 2 mg/m3 and transitional limit value of 3 mg/m3 (until 17 January 2023).
Table 2. Wood Dust Mass Concentration of Inhalable Dust and Samples Exceeding OEL (n) in the Total Number of Samples (N)
The highest inhalable mass concentration was measured around belt sander HS II, where 4 samples out of 6 had a higher mass concentration than the limit value 2 mg/m3. Exposure levels for the inhalable fraction of oak wood dust around HS II were 1.569 to 3.710 mg/m3.
Significant exceeding of the limit values for inhalable wood dust was recorded at workspaces at the CNC II (without suction) 4 samples out of the 7 having a higher mass concentration than the limit value of 2 mg/m3. Exposure levels for the inhalable fraction of the oak wood dust around the CNC II were 1.075 to 2.569 mg/m3.
During milling and planing (CNC and 4SP) measured exposures were below the transitional limit value of 3 mg/m3.
The measured values of inhalable and respirable dust mass concentration are shown by a distribution diagram of mean values in Figs. 1a and 1b, respectively. The distribution diagram in Fig. 1a presents two groups of inhalable mass concentration data for woodworking machines, one group with a lower mass concentration (CNC I and 4SP), and the other group with a higher mass concentration and greater data dissipation (CNC II and both types of hand sanders – HS I and HS II). According to the mean values of the respirable mass concentration from the diagram in Fig. 1b, the highest mass concentration and data dissipation was observed for woodworking machine HS II, whilst the other machines are in a group of lower, similar mass concentration levels.
Fig. 1. Distribution diagram of mean values and data dissipation of wood dust mass concentration for wood processing machines (a) inhalable and (b) respirable particles (SD- standard deviation; SE- standard error of mean)
The results of statistical testing of inhalable mass concentration from different woodworking machines showed that not only was there a significant difference between these two groups of samples, but also between the two woodworking machines (CNC I and 4SP), in the group with lower mass concentration (Table 3). The lowest mass concentration of inhalable dust measured near CNC I was lower than the mass concentration measured near the four-side planer (p = 0.004). There was no significant difference between the inhalable mass concentration for workspaces in the group with a higher mass concentration (CNC II, HS I and HS II). The mass concentration of respirable fraction measured near all observed machines did not significantly differ, except for HS II in correlation with CNC I and 4SP, from the above-mentioned group with a lower mass concentration (Table 4).
The geometric means and ranges of respirable mass concentration obtained at different workspaces are presented in Table 5. The highest exposure level for respirable oak wood dust was measured around belt sander HS II, and ranged from 0.243 to 1.342 mg/m3. The share of respirable particles in the inhalable fraction ranged between 12% and 31%, which is approximately 19% of the inhalation fraction on average. The highest share of respirable particles in the inhalable mass concentration were recorded at the woodworking places, with the lowest concentration of inhalable dust near CNC I.
Table 3. Probability Values From Statistical Testing of Inhalable Wood Dust Mass Concentration
Table 4. Probability Values From Statistical Testing of Respirable Wood Dust Mass Concentration
Table 5. Wood Dust Mass Concentration of Respirable Dust and Cr / Cinh Ratio
Fig. 2. Correlation diagram of respirable and inhalable mass concentration in the furniture factory
The distribution of respirable mass concentration had a very strong correlation (R = 0.78) with the inhalable dust mass concentration for all workspaces in the furniture factory, and is presented in Fig. 2. In a strong linear relationship, the mass concentration of respirable fraction increased with the increase of the mass concentration of inhalable fraction. During sampling of inhalable wood dust fractions in a low-risk working atmosphere, with mass concentration below 2 mg/m3, the respirable mass concentration was below 0.4 mg/m3.
A medium strong correlation (R = 0.51) was found between the share of respirable in inhalable mass concentration and inhalable mass concentration measured in the furniture factory (Fig. 3.) The share of respirable mass concentration in inhalable dust mass concentration decreased with the increase of inhalable dust mass concentration. The share of respirable in inhalable mass concentration for samples with inhalable mass concentration exceeding 2 mg/m3 is lower than 16% with a slightly decreasing tendency.
Fig. 3. Correlation between the share of respirable in inhalable wood dust mass concentration and absolute value of inhalable mass concentration in the furniture factory
Exceeding the OEL Exposure
From the results obtained, it is evident that workers at the workspaces of machines without an exhaust are exposed to higher mass concentrations of hardwood dust than 2 mg/m3, which represents exposure to an increased risk. Out of a total of 30 samples collected at 5 workspaces, 7 (23%) exceed the OEL. In the EU25 Member States, an increased risk of worker exposure to inhalable wood dust refers to 41% of workers being exposed to mass concentrations of up to 2 mg/m3. About 280,000 workers (32%) in the European manufacture of furniture were exposed to a level of increased risk, above 2 mg/m3 mass concentration of inhalable wood dust. The probability of exceeding the OEL, when comparing the estimated concentrations against the Dutch OEL of 2 mg/m3, was 75%. For the current OEL of 1 mg/m3 this probability was 95% (Spee et al. 2006). In the Italian wood industry, which uses active IOM during the sanding process, 85% of inhalable samples exceeded 2 mg/m3, and in planing and shaping, 16% of samples exceeded 5 mg/m3 (Campopiano et al. 2016).
In furniture factories in New Zealand, the occupational exposure limit of 1 mg/m3, recommended by the American Conference of Governmental Industrial Hygienists, was exceeded in 19% of measurements, which represent an average lower inhalable dust exposure of 0.6 mg/m3. Personal exposure to inhalable softwood dust for 7% of workers exceeded the New Zealand workplace exposure limit of 2 mg/m3 (Douwes et al. 2017). In the Croatian furniture factory there were 16% of cases with higher mass concentration than the limit value of 1 mg/m3 for respirable hardwood dust, and 19% of cases higher than the limit value of 3 mg/m3 for total hardwood dust (Kos et al. 2004). During the processing of dry oak wood and beech wood in the factory and in the carpentry near the four-side planer, drum sander and circular saw, the mass concentrations of the inhalable fraction for 48 samples, of a total 119 inhalable samples (40%), exceeded the limit value of 2 mg/m3 (Čavlović et al. 2021).
Exposure level to respirable particles and its influence on health effects
Most studies assessing the risk of upper or lower respiratory tract disease due to exposure to wood dust, in odds ratios (OR) calculation, have taken into account the influencing factors (intensity, frequency and duration of exposure to various occupational sources of wood dust, job category, company size, activity sector, geographical location and many others) including tobacco smoking. In risk estimation on the basis of occupational history data collected by hospitals in Italy, with no quantitative assessment of exposure to wood dust, Soćko (2021) found a relationship between the duration of occupational exposure to wood dust and the relative risk of developing cancer in all sinonasal epithelial cancer cases. The most important calculation found here was that, with the increasing duration of exposure, even in the short term, the risk of exposure to wood dust also increases. He found a higher risk for sinonasal adenocarcinoma (OR = 3.49) for a person who works 7.75 years than for sinonasal epithelial cancer (OR = 2.42). The risk calculated is important for discussion because younger workers with a shorter duration of exposure to wood dust, of between 5 and 10 years, participated in our research. A US 12 case-control study found a doubled risk, statistically significant for sinonasal cancer in men employed in any wood-related job (OR = 2.0, 95% CI: 1.6 to 2.5) in comparison to men who had never worked in a wood-related job. The relative risks associated with exposure to wood dust and wood-related jobs indicate a significant risk of developing sinonasal cancer in men employed in any furniture factory (OR = 13.5, 95% CI: 9.0 to 20.0). The exposure categories, zero and low, medium and high exposure, were created in the range from 0 to 5 mg/m3, and OR for risk assessments were calculated to be 0.6, 3.1 and 45.5, respectively (Demers et al. 1995). The results from another US based case-control study show that the case of individuals reporting 20 or more years of “regular” wood dust exposure was associated with a statistically significantly increased risk of 32% for all upper aero-digestive and respiratory cancers, and 69% for lung cancer alone (Jayaprakash et al. 2008). An industry-based case-control study was conducted in the German woodworking industries and showed that average exposure to inhalable wood dust ⩾ 5 mg/m3 was associated with a high risk (OR 48.47, 95% CI: 13.30 to 176.63) for sinonasal adenocarcinoma, compared to levels below 3.5 mg/m3. Exposure between 3.5 and 5 mg/m3 was also found to pose a risk (OR 10.54, 95% CI: 3.34 to 33.27) (Pesch et al. 2008).
In this regard, it could not be concluded from the research in a Croatian furniture factory, based on two of the 30 exposures higher than 3.5 mg/m3, that workers working with sanders have a 10.54 times higher risk of sinonasal adenocarcinoma than those who are not exposed to wood dust at all. However, experts on this type of risk warn that the rarity of the disease does not exclude the risk of exposure even below these concentrations.
In four Nordic countries, by univariate analysis, a strongly increasing risk with increasing cumulative exposure (CE) to wood dust was observed for nasal adenocarcinoma, with a 29-fold increased risk in the highest CE category (28.82 mg/m3-years). In this study, the exposure to wood dust was generally low, below 5 mg/m3. Twenty-five years ago, some authors suggested that dust-related nasal adenocarcinoma could be eliminated in Europe and the United States if exposure to wood dust did not exceed 5 mg/m3 on average, because they assumed that this permissible level was safe, without taking into account cumulative exposure (Siew et al. 2017). However, the lack of this assumption is manifested in the fact that today’s regulations reduce the lower risk limit to 2 mg/m3.
In a case control study conducted in Germany a strong effect on laryngeal cancer risk was observed for high exposure of hardwood dust (OR = 2.6, 95% CI: 1.1 to 4.2) (Ramroth et al. 2008).
Inconsistent findings are often the reason for the conclusion of the IARC as to the lack of connection between occupational exposure to wood dust and the development of lung cancer (Bhatti et al. 2011). Some other research results support the hypothesis that wood dust exposure is a potential risk factor for lung cancer (Wiggans et al. 2016; Matrat et al. 2019; Scarabelli et al. 2021). Bhatti et al. (2011) observed an increased risk of lung cancer associated with working in a sawmill (OR = 1.5, 95% CI: 1.1 to 2.1), and found no evidence of increased risks with other occupations, working with wood as a hobby, or with an estimated cumulative exposure to wood dust for the highest compared to the lowest quartile of exposure (OR = 0.9, 95% CI: 0.6, 1.3). The adjusted OR for the combined wood dust related occupations and industries associated with the risk of lung cancer was 3.15 (95% CI, 1.45 to 6.86), and for the overall cumulative exposure measure it was 1.60 (95% CI: 1.19 to 2.14) (Barcenas et al. 2005). A health study in the USA woodworking industry estimates the effect of mixed wood dust exposure on annual changes in lung function. The only significant effect found was an obstructive effect of the respirable particles in the milling plant (mean exposure of 0.147 mg/m3), and the restrictive effect on annual changes in a worker’s lung function in the sawmill-planing plant from plywood (mean exposure of 0.255 mg/m3) (Glindmeyer et al. 2008). A number of respiratory symptoms suggestive of airway reactivity were significantly more common among the workers in a plant producing oriented strand board (OSB), where measurements of respirable dust ranged from 0.05 to 0.5 mg/m3 (Herbert et al. 1995).
The published level of exposure to respirable wood particles is common to most furniture manufacturing jobs, so harmful health effects to the respiratory system can be expected regardless of the level of exposure to inhalable hardwood dust (Vinzents et al. 2001). In this regard, the results of this study show that there is a very low, but present, occupational health risk when working on the two observed machines, CNC I and 4SP, with measured low mass concentrations of respirable particles, where the geometric mean amounts to 0.069 mg/m3 and 0.105 mg/m3. Additionally, occupational exposure to wood dust has a significant impact on allergies due to extractive volatiles and microbial components from certain wood species (Teschke et al. 1999; Sabolić Pipinić et al. 2010; Ljubičić Čalušić et al. 2013; Straumfors et al. 2018). The health effects of occupational asthma, pulmonary dysfunction, and elevated respiratory symptom levels have been reported in sawmill workers, despite an average inhalation concentration of pine and spruce dust of 1.35 mg/m3 (range, 0.1 to 2.2 mg/m3), with levels below the current occupational standard (Hessel et al. 1995).
The share of respirable in inhalable wood dust mass concentration
In the USA wood processing industry, overall geometric mean exposure levels were found to be 1.44 and 0.18 mg/m3, for the inhalable and respirable fractions respectively. On average, for all samples, the respirable fraction accounted for 16.7% of the mass of inhalable dust. Processing of hardwood and mixed woods generally were associated with higher exposures than were softwood and plywood (Kalliny et al. 2008). In the Polish furniture industry, the mass concentrations of inhalable dust were from 1.34 to 22.13 mg/m3, and the respirable fractions from 0.38 to 4.04 mg/m3, which is approx. 25% of the inhalable fraction on average (Szewczyńska and Pośniak 2017).
In other research, the share of respirable mass concentration in the total mass concentration is the highest, being over 50% for samples of total mass concentration lower than 1 mg/m3 and rapidly decreasing with the increase of total mass concentration. The share of respirable particles in total wood dust, for samples with a total mass concentration exceeding 2 mg/m3, is lower than 40%, with a slightly decreasing tendency. The highest share of respirable particles in wood dust are recorded at workspaces with a low concentration of total wood dust, and in the vicinity of machines whose cutting parameters result in lowest thickness of wood chips, such as when cutting boards with a circular saw (Kos et al. 2004). Some authors confirmed that coarse sand paper produced more dust than fine sand paper (Galea et al. 2009). A comparison in this article of these two types of hand sanders, and an orbital and belt sander, shows that less dust is produced when HS I sanded with finer sand paper (120, 150 and 180) than HS II with coarse sand paper (80). The proportion of respirable particles in the inhalable dust produced by the orbital sander is lower (14%) than for the belt sander (20%) (Table 5).
The influence of wood processing parameters on dustiness
The highest concentrations occurred in sanding and the lowest occurred during milling processes of materials used in the manufacture of furniture (Kos et al. 2004; Ljubičić Čalušić et al. 2013). The concentration of respirable dust was affected only by the sanding pressure, and it increased linearly with increasing sanding pressure, while the granulation and sanding direction were not affected (Zhao et al. 1999). Dust-generation is higher when sanding low density wood at a high wood removal rate using fine abrasive grits. In the furniture factory, the exposure to hardwood dust during orbital hand sanding was 26 mg/m3, and during manual sanding 19 mg/m3 (Ratnasingam et al. 2011). In a typical cabinet-making workshop, slightly higher exposure levels for the inhalable fraction near the hand sander operator were 6.9 to 76 mg/m3 for MDF and 2.5 to 45 mg/m3 for softwood. The respirable fraction levels were 1.3 to 6.4 mg/m3 for MDF and 1.2 to 2.9 mg/m3 for softwood (Hursthouse et al. 2004). In previous research, higher concentrations of hardwood dust were generated by sanding than have been observed in this research. Vacuum extraction on hand tools, combined with a downdraft table, reduced exposures by 42.5% for routing and 85.5% for orbital sanding (Spee et al. 2006). The orbital sander experiments showed a small reduction in inhalable dust exposure of 8.3% when using the downdraft table (Douwes et al. 2017).
In carpentry, the use of hand tools, orbital and band sanding, showed 3.0 to 3.4 times higher exposure to inhalable dust compared to gluing (which was selected as the reference category) (Douwes et al. 2017). Higher exposure to dust was also found for CNC work, averaging 2.4 mg/m3 (ranging from 1.5 to 4.0 mg/m3). The use of hand tools and conventional cleaning methods (dry wiping and sweeping) significantly contributed to high exposures in joinery workers, whilst use of vacuum extraction on hand tools and alternative cleaning methods were shown to have the potential to significantly reduce dust exposures (Kos et al. 1999; Douwes et al. 2017). Local exhaust ventilation on a hand sander reduces the exposure to wood dust by a factor of 3 to 10. Use of a flat sander instead of a belt sander yields a reduction of exposure by a factor of 5 to 10 (Spee et al. 2006). This research provides guidelines for future research that will focus only on certain influencing factors such as the type of sand paper or downdraft table in the sanding process.
CONCLUSIONS
- The use of new generation woodworking machines with suction ensures a lower risk of occupational exposure to wood dust, especially the hardwood of oak that is classified as a cancerous substance. Exceeding the occupational exposure limit (OEL) value of 2 mg/m3 for the mass concentration of hardwood dust, occupational safety poses a health risk from a number of respiratory diseases. The results of this research confirmed that the least dust is produced by milling and planing. Worker exposure may be below the level of increased risk if a machine such as a planer or computer numerical control (CNC) router is connected to a quality central suction system. Therefore, there is the least dust in the new production plant with a CNC machine of newer technology connected to a central exhaust. In contrast, a similar older suction-free CNC machine has 57% of samples above the increased risk limit.
- To reduce the risk of harmful effects of wood dust from sanding with hand sanders, the best solution to reduce the dust is to use a combination of a suction filter bag and a downdraft table. Protecting workers from the risk of exposure to wood dust would be helped by changing the workspace so that an individual worker does not work for more than 10 years at a workspace with a higher risk, especially a worker with poor general health and with a predisposition to disease.
- Due to the higher risk of upper respiratory tract disease, the protection measures prescribed by OEL apply only to the inhalable fraction of wood dust. The risk of lower respiratory tract diseases also increases with higher exposure to inhalable particles, because it increases the exposure to respirable particles proportionally, so OEL is also an indirect measure of protection against exposure to respirable particles.
ACKNOWLEDGMENTS
This research was co-funded by the European Fund for Regional Development, grant number KK.01.2.1.02.0031. The article was published as part of the project “Development of innovative products from modified Slavonian oak” by Spin Valis d.d. and partner University of Zagreb Faculty of Forestry and Wood Technology. The total value of the project is HRK 55,064,343.84, while the amount co-financed by the EU is HRK 23,941,527.32. The project was co-financed by the European Union from the Operational Program Competitiveness and Cohesion 2014-2020, European Fund for Regional Development.
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Article submitted: April 15, 2022; Peer review completed: July 11, 2022; Revisions accepted: August 17, 2022; Published: August 24, 2022.
DOI: 10.15376/biores.17.4.5831-5847