Wood is processed worldwide and occupational exposure to wood dust is affecting millions of workers. Exposure to wood dust has been associated with health issues due to the natural chemicals in the wood, or substances in the wood such as bacteria, molds or fungi.
Wood dust is also associated with toxic effects, irritation of the eyes, nose and throat, dermatitis and respiratory system effects which include decreased lung capacity and allergic reactions. Clinical case series on wood dust-related asthma or rhinitis reported more than 20% of the cases are sensitized to wood dust. Wood dust is also a safety concern because it can cause a fire or explosion.
Routes of Exposure to Wood Dusts
The chemicals in the wood may be absorbed into the body through the skin, lungs or digestive system. The dominant route of human exposure to wood dust is inhalation. Because of the wide distribution of wood dust particle sizes, there is potential for deposition throughout the respiratory system. However, the majority deposit in the upper airways, primarily in the nose. This correlates well with observations that some of the most important health effects, such as upper respiratory symptoms occur in the upper airways. However, there is also strong evidence for effects deeper in the respiratory system from finer dust.
Dermal contact also occurs routinely, occasionally causing dermatitis. In the case of exposure to some tropical species, the risk of contact or allergic dermatitis may be great.
When the body absorbs the chemical, the chemical may cause headaches, loss of weight, breathlessness, giddiness, cramps and irregular heartbeat.
Other products used on or in wood may also have hazards. Resins, pesticides, paint, paint strippers, glues, adhesives, waterproofing compounds, lacquers, varnishes, sealants, dyes and other products are examples.
Wood Species
Some people are sensitive to certain species of wood, wood dust, or wood oils. There are ∼73,000 tree species globally and more than 1000 of these are used for commercial purposes. The major part (about 95 weigh percent) of wood is composed of cellulose, hemicellulose and lignin. The remaining 5% are numerous other high and low molecular weight organic and inorganic compounds, including proteins. Examples for low molecular compounds are terpenes, terpene derivatives like abietic acid, phenolic compounds, tannins, stilbenes, flavonoids, and glycosides, many with known sensitizing and irritative properties.
Different wood species have different toxicological and allergenic potential due to the different chemical composition including protein content. Tropical woods in general have a higher content of volatile and non-volatile compounds compared to wood types from other climate zones. Studies showed a clear positive dose-dependent relation indicating that the level of exposure among woodworkers has an impact on the sensitization rate, which has also been seen in other industries, e.g. bakers and lab animal workers.
Wood Processing
Wood dust is created during all stages of wood processing such as sawing, routing, sanding and other operations. Inhaled wood dust is hazardous to long-term health. All woods produce fine dust when worked, which in turn can damage the lungs and cause a number of other adverse health reactions. Workers can also be exposed when the dust becomes airborne such as when removing dust from furniture, maintenance activities, or when cleaning equipment (e.g., emptying the bag from a dust extraction system or vacuum).
Dermatitis
Chemicals in many types of wood can cause dermatitis, a condition in which the skin can become red, itchy, or dry, and blisters may develop. With repeated exposures, a worker can become sensitized to the wood dust and develop allergic dermatitis. Once a worker becomes sensitized, exposure to small amounts of dust can cause a reaction that becomes more severe with repeated exposures. Allergic dermatitis is most often caused by exposure to tropical hardwoods such as obeche, mahogany, and rosewoods.
Respiratory System
Respiratory system effects to wood dust include decreased lung capacity and allergic reactions in the lungs. These diseases are caused by molds growing on the wood rather than the wood dust itself.
Two types of allergic reaction can take place in the lungs: hypersensitivity pneumonitis (inflammation of the walls of the air sacs and small airways) and occupational asthma. Decreased lung capacity is caused by mechanical or chemical irritation of lung tissue by the dust. This irritation causes the airways to narrow, reducing the volume of air taken into the lungs and producing breathlessness. It usually takes a long time to see a reduction in lung capacity.
Softwood dusts may reduce lung function. Studies showed that workers who smoked and were exposed to wood dust were more greatly affected than workers who did not smoke. This condition can worsen during the work week and improve during a worker’s days off. Over the long term, some workers may develop a permanent decrease in lung function (chronic obstructive lung disease).
Hypersensitivity pneumonitis appears to be triggered when small particles penetrate deeply into the lungs where they trigger an allergic response. Particles that are known or suspected to cause this condition include molds, bacteria and the fine dust. The initial effects can develop within hours or after several days following exposure and are often confused with flu or cold symptoms (headache, chills, sweating, nausea, breathlessness, and other fever symptoms). Tightness of the chest and breathlessness often occur and can be severe. With exposure over a long period of time, this condition can worsen, causing permanent damage to the lungs. The walls of the air sacs thicken and stiffen, making breathing difficult.
Occupations
Some of the occupations at increased risk for exposure to wood dust include the workers employed in logging, sawmills, furniture, cabinet making, carpenters, cleaning, or maintenance staff – activities where wood dust is generated or reintroduced, construction workers and shipbuilding workers.
Fine dust that results from the processes such as shaping, routing and sanding are associated with higher exposure levels. Hardwoods generally produce more dust than softwoods when worked in similar conditions. Dry wood tends to produce more dust.
The chemicals associated with allergic reactions are usually found in the inner parts of a tree, e.g., the heartwood. The workers most often showing reactions are those who do secondary wood processing (e.g., carpenters, joiners and finishers).
Controlling Exposure to Wood Dust
Providing appropriate education and training that informs employees about the hazards of wood dust exposure, safe work procedures, how to identify when a ventilation system is working appropriately and the importance of control measures.
Knowing which types of wood is being used and all hazards associated with that wood. Substituting with another type of wood with no or fewer known health effects, where possible.
Reducing dust generation. Using a local ventilation exhaust and a high-efficiency particulate filter.
Significant exposure can happen when cleaning (e.g., emptying dust bags) or maintaining equipment. Practicing good housekeeping. Keeping surfaces and floors clear. Using cleaning methods that reduce re-introducing the dust into the air. Using wet clean-up methods.
Wearing respiratory protection when appropriate. Using protective clothing and gloves to reduce skin exposure. Practicing good personal hygiene (e.g., wash or shower to remove dust from skin). Washing hands and face when finished a task, and before eating or drinking. Cleaning clothes by washing or using a vacuum when washing facilities are not available. Bagging and sealing dust waste to prevent dust from re-entering the air.
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