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Energy & Fuels
Risks threatening human health and safety during work in the process of production and storage of forest biomass can also be divided according to individual production phases: establishment and cultivation of plantations of fast-growing trees and intensive stands; production of forest chips from various forms of forest biomass; transport of biomass; and storage of forest biomass for energy purposes.
- forest biomass
- biomass storage
- fungi
1. Production of Forest Biomass as a Renewable Energy Source
Forest biomass has long been among the promising and renewable sources of energy. It is actually used as a source for the production of heat, electricity, biogas, and biofuels [1,2,3,4]. Biomass (including the biodegradable part of waste) is undoubtedly one of the most important renewable energy sources in the European Union. It makes up 63.3% of the total production of energy from renewable sources. Agriculture and forestry are therefore extremely important from the point of view of energy production from renewable sources [5,6,7,8,9,10].
With increasing demands on the quality and quantity of produced biomass, the main element of the knowledge-based economy is the person and the issue of safety and health protection at work. With the development of technology and automation, working conditions improve, but at the same time, the demands placed on workers increase. This is also why the number of occupational accidents in forestry and agriculture does not decrease fundamentally [11,12,13,14,15,16,17].
Potential sources for the production of biomass and forest chips from it are mainly harvesting slash, purpose-grown plantations of fast-growing trees, or energy stands, Smallwood from cuttings and thinnings, or the crown parts of harvested trees, unsuitable for the production of higher-quality raw-wood assortments [18,19,20,21]. Obtaining wood chips from trees grown for energy purposes, but also from harvesting slash, is a complex technological process and requires certain technical equipment. Work is influenced by various factors and brings many health and safety risks for workers [22,23]. Wood biomass is an important renewable energy source. Its share in energy production increases every year. The share of production of raw wood assortments, which are the primary source for the production of wood-based energy sources, is also increasing. According to FAO data, the share of produced wood-based energy sources in the total volume of produced wood products is approximately 11%. In the Slovak Republic, fuelwood assortments make up approximately 8% of all harvested wood assortments. The estimated biomass production in the world is more than 100 billion metric tons per year. Biomass production and its potential to produce renewable bioenergy varies among countries and world regions, and with availability of resources, biodiversity, technology, and economical factors [1,22].
2. Risks in the Process of Production and Storage of Forest Biomass for Energy Purposes
The general risks that are always present at every stage of biomass production for energy purposes include the risks of work accidents, occupational diseases, property damage, and general danger. All these risks have a common denominator, which is the human factor and the approach of workers to the implementation of individual work activities. In general, it can be stated that occupational accidents are a common risk to human health in every production phase. The human factor is an important variable that fundamentally affects the quality of the work performed and the safety during it. However, work accidents often occur as a result of unforeseen circumstances and therefore their occurrence cannot be completely eliminated. The greatest risk of a work accident directly depends on the specific phase and the work activities performed in it. In general, the highest risk of a work accident in forestry is during the harvesting process. Analyses and statistics of the incidence of occupational accidents in forestry were processed in several works [28,29,30,31,32,33,34]. These works confirm that almost a third of all work accidents in forestry occur in the process of harvesting, with the most risky days of the week being Monday and Friday. The most frequently injured parts of the body are hands and feet. The second most risky work operation is wood skidding. In other words, the initial stages of the production of wood and biomass for energy purposes are the most risky from the point of view of work accidents. Statistics and analyses of the work accident rate are constantly supplemented and thus enable the formulation and adoption of effective measures for improvement in this area. In most cases of domestic and foreign small and medium-sized enterprises in the field of forestry, employers do not pay enough attention to the safety and health of employees, and regular health examinations of persons working in dangerous working conditions are not carried out [33,35,36,37,38,39,40,41].
The predominant cause of most forest harvesting accidents is the use of unsafe practices and non-compliance with established prohibited work practices. The majority of serious work accidents while working in the forest were caused by non-observance of safe working or technological procedures. In order to ensure safe working conditions, it is necessary to study and analyze real cases of accidents and work injuries, and then create a system of measures and requirements to prevent the occurrence of these phenomena. Due to the large number of fatal and serious work accidents in the processes of harvesting and skidding of wood, the importance of systematic education of workers who perform work in this industry is increasing.
2.1. Risks in the Establishment, Cultivation, and Protection of Fast-Growing Tree Stands
In the establishment, cultivation, and protection of cultures of fast-growing trees, in addition to the group of work accidents, chemical harmful factors and biological harmful factors can also be characterized as health risks. Chemical agents are used quite often in the cultivation of fast-growing trees. Pesticides and insecticides are used to kill pests and insects. Herbicides, in turn, fight against weeds (Figure 1). Herbicides used contain phenoxy, glyphosate or triazines [42]. With the long-term use of areas for plantations of fast-growing trees, with repeated application of glyphosate, the survival of the planted individuals improves, but there is a gradual decrease in production [43]. All the chemical agents used to fight weeds have a demonstrably negative effect on human health. Glyphosate-based herbicides have a significant negative impact on human health, and their carcinogenic effect has also been proven, or has been listed as probable human carcinogens by the International Agency for Research on Cancer [44,45,46,47,48].
Figure 1. Weeding of the plantation area using pesticides.
The toxicity of glyphosate on human cells has been confirmed by several studies, some studies state that the safety of the use of herbicide preparations based on glyphosate cannot be unequivocally confirmed from the point of view of epidemiological studies [49]. A harmful effect on the eyes was also confirmed in 70% of workers who used Roundup herbicide [50]. A direct effect on the incidence of prostate cancer among workers who regularly worked with herbicides was also confirmed. The paper [51] examined the incidence of prostate cancer in a sample of 55,332 men who used 45 types of pesticides, identifying a normalized ratio of prostate cancer incidence of 1.14 (95% confidence interval 1.05, 1.24).
It is clear from the above that the use of pesticides represents a wide spectrum of health risks for people. In addition, they have demonstrably adverse effects on the environment, ecology, and biodiversity in forest and agricultural ecosystems (e.g., [59,60]).
Biological factors in the establishment of plantations include the risk of being bitten by the common tick (Ixodes ricinus), which can cause severe disease [61,62]. Among the most serious diseases that can be caused by a tick bite are Lyme disease (borreliosis) and tick-borne encephalitis. The diagnosis of borreliosis is always established on the basis of the clinical picture and microbiological diagnosis [63]. Tick-borne encephalitis is an acute febrile disease affecting the central nervous system (meningitis and encephalitis), for which there are vaccines. The incidence of this disease in Europe has increased by more than 400% since 1974 [64]. Global climate changes also have an influence on this fact. Data show that the winter activity of ticks is increasing [65], their life cycle is accelerating [66,67], they are found at higher and higher altitudes [68,69] and are increasingly found in more northern regions of Europe [70].
.2. Risks in the Production of Biomass for Energy Purposes and Wood Chips
The production process of energy wood and forest chips can be divided according to the production location and also according to the chosen technological procedure and technologies. This also results in potential risks in this technological process. In addition to work accidents, which are a standard risk for all activities, there are also described biological risks resulting from tick bites when working in the field and the forest. Other factors in this phase include mechanical risk factors, stress due to cold and heat, exposure to wood dust and dirt, long-term excessive unilateral loading of the limbs, and psychosocial risks [71,72].
Regarding the mechanical risk factors in this production phase, our advice is mainly related to noise and vibrations, which affect the operators operating the machines for the production of biomass. Despite the legislative obligation of workers to use personal protective work equipment, often workers do not use this equipment or do not change them at the prescribed intervals. This is also why occupational diseases constantly occur. As a result of long-term exposure to vibrations, vasoneurosis, vascular problems, chronic pain and limited limb mobility occur [73]. Long-term exposure to noise is mainly associated with partial or complete hearing loss, sleep disorders, psychological problems, and headaches [74,75,76,77]. Professional traumatic angiopathy (vibration white finger) or vessel damage syndrome occurs as the first signal damage to the body by vibrating instruments [78].
According to Slovak legislation, noise-induced hearing loss is classified as hearing loss according to “Fowler” in victims under 30 years of age of at least 40%. For aggrieved persons older than 30 years, this is every two years + 1%, until the aggrieved person reaches 50 years of age when the hearing loss must already exceed 50%.
With multi-operation machines, machine operators are exposed to two types of vibrations: vibrations transmitted from the steering wheel to the hands and vibrations transmitted from the machine seat to the whole body [79]. In most of the works, none exceeding the permitted limits established by the legislation was found for modern machines [80]. According to the current Slovak legislation (Government Regulation No. 416/2005 on minimum health and safety requirements for the protection of employees from risks related to exposure to vibrations), the limit value of the normalized acceleration of vibrations transmitted to the whole body in the direction of the axis with maximum transmission is at the level of 1.15 m·s−2. The limit value of the resulting normalized acceleration of vibrations transmitted to the hands ahv,8h,L is 5 m·s−2. Exceeding these values was not confirmed for the analyzed chippers [80]. This long-term (several years) effect of such vibrations on a person and the effect on his health is problematically evaluated. When chipping with chippers, the technological parameters of the machine itself have the greatest impact on exposure to whole-body vibrations, while the wear of cutting tools did not show a statistically significant increase in these vibrations [74].
The layout and impact of vibration acceleration on the hands depends on the layout of the control elements of the individual mowers, as well as on the work operation that is being performed. An increase in vibrations can occur, e.g., when the material gets stuck in the feeder, but also when chipping very thick pieces that need to be adjusted with a hydromanipulator [80]. The risk of increased vibrations acting on the hands must also be approached individually depending on the technological process during chipping (machine parameters, chipped material, and weather conditions).
As with vibrations and noise, workers with a chainsaw operator profession, workers with a physical age of 56–60 years, and workers with a working period of 26–30 years are among the most at risk [77]. The work [74] evaluated the noise on drum chippers Pezzolato PTH 1200/820 and PTH 800/820, which were placed on the construction of a truck and on a separate trailer behind the tractor, respectively. They found that higher noise was produced by chippers that were placed on a separate trailer. At the same time, it was confirmed that with chippers that have a closed cabin, and the operator is “isolated”, the action and limit values for noise exposure were not exceeded. Fundamental differences in the acoustic noise level were not detected depending on whether whole tree trunks were chipped or only harvesting slash and coarse material. Most modern machines with closed cabins already offer modern ergonomic solutions that significantly limit the negative impact of noise. The problem arises with mowers where the operator stands or sits outside the cab and operates the mower directly.
The risk of inhaling wood dust by the mower operator is also associated with outdoor chipping work (Figure 2). A level of 5.0 mg·m−3 of air is considered a hygienic technical reference value for the concentration of wood dust.
Figure 2. Swirling of wood dust in the wood chipping process.
The impact of wood dust on human health depends on many factors such as the type of wood, its chemical composition, and other factors. In addition to the effect of dust on the respiratory system, it also has a negative effect on the mucous membranes of the eyes, nose, mouth, and larynx [83,84]. The result of the great impact of small dust particles on the mucous membranes is their drying; on the other hand, dusts with higher humidity create conditions for fermentation, the formation of chemical reactions of dust particles with biological particles that are contained in the dust and also create a danger of developing allergies in the human body [85]. Wood dust can further cause [86,87] the following:
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Dermatoses—caused by mechanical irritation, chemical irritation, and allergic effects of some wood components;
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Respiratory problems—affected by particle size and type of wood (inflammation of mucous membranes and airways);
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Allergic respiratory problems—allergies to components of wood dust (asthma, bronchitis), allergies to molds and fungi in wood;
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Carcinogenic action of some types of wood.
The greatest danger for the respiratory organs is represented by the respirable (alveolar) component with a particle size below 10 µm, which reaches the lungs (lung tissue) through the respiratory tract and acts as a mechanical or chemical irritant.
During the production of wood chips, wood dust often swirls in cloud concentrations, which, especially in combination with fuel vapors and engine heat, can create a dangerous explosive mixture that can endanger the life and health of workers, as well as cause damage to property and equipment [90,91].
Another health threat to workers in the chip production process is disease from long-term, excessive, and one-sided loading of limbs (Carpal tunnel syndrome). The disease arises in connection with the long-term physical exertion of workers and mainly affects the structures of the movement system of the limbs’ bones, joints, tendons, muscles, nerves, and blood vessels [92,93].
Operators of multi-operational machines are primarily exposed to excessive neuropsychological stress. They are forced to perform short work cycles, perceive, and evaluate a large amount of information, and make a large number of quick decisions. In work [95], they investigated the influence of external factors on the pulse frequency of harvester and forwarder operators. They found that operators’ physical parameters, machine types, controller parameters, workplace lighting intensity, equivalent noise, and whole-body vibration affected approximately 72% of the sample with an elevated pulse rate. The issue of assessing psychosocial factors affecting workers in forestry is very difficult and requires the participation of several experts. However, with the current level of mechanization and technologies used, assessing the neuropsychic load is a necessity. It is necessary to implement this type of risk in occupational risk assessment systems and, based on the results, propose measures for their elimination, or complete removal [22]. The second important factor that can cause stress and subsequent neuropsychological disorders is workplace relationships.
2.3. Risks in the Process of Storing Biomass for Energy Purposes
With the increase in the number of operations using wood chips as an energy source, issues of health and safety risks during their storage are becoming more and more common. From this point of view, the risks associated with the activity of fungi and molds in piles of wood chips (Figure 3) and the inhalation of wood dust when handling wood chips are evaluated as the most risky factors for human health [97,98,99,100,101].
Figure 3. Mycelia and fruiting bodies of fungi on a stored pile of wood chips.
Examples of smaller piles of wood species are Beech (Fagus sylvatica), Poplar (Populus tremula), and Spruce (Picea abies). In total, 12 genera or species of fungi and molds were identified in these piles. Statistical analyses did not confirm a significant dependence on the occurrence of fungi on the wood or the level in the pile. The most represented species of fungi and molds in the experimental piles were mainly Mucor sp., Penicillium sp., Trichoderma sp., and Aspergillus fumigatus [98].
This poses a risk even if the chip storage is located in an urban area near houses or apartment buildings, which is quite common in the case of urban-type heating plants. Since fungal and mold spores can spread in dangerous concentrations up to a distance of 300 m from the pile, these residents are potentially at risk of this health risk without knowing and being informed about it [102].
The immediate use and consumption of produced forest chips is often not possible for various reasons. Technologies that demand a particular quality of wood chips are often installed in heating plants. These heat producers are increasingly demanding continuous supplies of high-quality wood chips. They mainly focus on the moisture content and calorific value of the fuel, which also limits its final price.
It was found that the amount of spores in the air drops below 1000 CFU·m−3 (Colony Forming Unit·m−3-colony forming unit (CFU) per cubic meter) up to a distance of 300 m from the pile. It is therefore possible to consider this space as a threatened zone, with a potential health risk [102].
Most of the fungi identified in the chip storage process pose a potential hazard to human health when inhaled by humans. Inhalation occurs quite often when handling wood chips (loading, unloading, dispensing into a container, etc.). Fungi of the genus Aspergillus sp. and Fusarium sp. cause invasive mycoses (infections) that affect internal organs and organ systems [22,27,103]. Species of Aspergillus sp. can cause lung disease aspergillosis in the form of pulmonary aspergilloma, which can cause up to 20% mortality [104]. Fungi of the genera Mucor sp. and Fusarium sp. are a threat, especially for people with weakened immunity. They can cause various infections (e.g., “mucormycosis”) and are considered important allergens [105,106]. The production of dangerous mycotoxins was also confirmed in the genus Penicillium sp. They also cause allergic diseases in some people [107]. Fungi of the genus Trichoderma sp. cause infections in immunosuppressed people [108].
The initial heating of fresh chips is caused primarily by the respiration of still-living parenchyma cells. When the chips are heated above 40 °C, cell respiration stops. Further heating of the pile is demonstrably caused by the metabolism of fungi and bacteria. Fungi survive up to a temperature of about 60 °C, but thermophilic bacteria raise the temperature of the chips to a value greater than 75 to 80 °C, at which point their activity stops. Despite this, long-term stored biomass can reach temperatures greater than 100 °C. Above this limit, the processes of thermochemical conversion and chemical oxidation begin, which can lead to spontaneous combustion. Even when the temperature reaches more than 80 °C, the chips are not disinfected, because the microorganisms survive in a state of rest. After subsequent cooling, they become active, and the temperature of the pile may rise again.
These facts extremely increase the risk of fire, which can cause damage to property and human health. This risk is often further increased by the incorrect location and spatial arrangement of the woodchip storage in operations (Figure 4), together with non-compliance with safety regulations (e.g., incorrect location of the ash dump, storage of a large volume of woodchips without creating the least one internal line, missing area intended for spreading ignited woodchips, insufficient equipment for fire extinguishing, protection against the entry of unauthorized persons, etc.).
Figure 4. Inadequate spatial arrangement of the chip storage—a pile and a nearby ash dump.
This entry is adapted from the peer-reviewed paper 10.3390/en17051064
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