Wood Dust

The wood processing industry is the second largest manufacturing industry in Australia. It employs around 85,000 people, mostly in manufacturing and in forestry and logging operations. Many workers in workplaces such as pulp and paper mills, sawmills, veneer and plywood plants, woodchip operations, joineries and furniture plants may be exposed to high levels of wood dust. Occupations such as carpenters and roofers, and maintenance workers in construction industry can also be exposed to wood dust regularly.

Wood is one of the major renewable resources in the world. For industrial purposes, wood is classified into two types; hardwoods (derived from deciduous trees, for example Eucalyptus) and softwoods (derived from coniferous trees, for example pine). Eucalyptus, which is native to Australia, is the most abundant hardwood species processed in sawmills and chip mills. As native hardwoods are expensive, some joinery and furniture operations process imported timber together with reconstituted softwood.

The major woodworking processes are debarking, sawing, sanding, milling, lathing, drilling, veneer cutting, chipping and mechanical defibrating. Sanding and sawing processes produce fine airborne dust particles. High moisture content in fresh wood makes it less airborne than dry wood, which produces more dust during processing. Softwood particles are more fibrous and usually larger and as a result also less capable of becoming airborne.

Health effects of wood dust

Skin irritation and skin sensitisation

Skin irritation can be caused by contact with the wood itself, dust, bark, sap or lichens growing on the bark. Symptoms subside once the irritant is removed. The Australian native timber Eucalyptus hemiphloia (grey box) and Eucalyptus maculata (spotted gum) are known to cause skin irritation not only by contact, but also by proximity.

Sensitization dermatitis is usually caused by exposure to the fine dust from certain wood species. This exposure produces symptoms similar to skin irritation. Once sensitized, the body sets up an allergic reaction, and will react severely when exposed even to a small amount of wood dust. For more information see Workers Health Centre’s table of reported wood allergies.

Allergic and non-allergic respiratory effects

The most commonly reported allergic respiratory effect due to wood dust exposure is asthma. It may occur alone or in conjunction with dermatitis. Occupational asthma and rhinitis due to exposure to Western Red Cedar has been well documented. It is one of the most common types of occupational asthma prevailing in British Colombia, Canada.

Exposure to wood dust can cause chronic obstructive lung disease. Exposure to saw fumes containing terpenes, a constituent of wood also causes chronic obstructive impairment in lung function.

Nasal effects

Chronic exposure to wood dust can cause impaired nasal mucociliary clearance. A major portion of airborne wood dust is contributed by particles larger than 10┬Ám size, which can be trapped effectively in the nasal passage.

Nasal cancer is a significant hazard of woodworking and is particularly associated with hardwoods.

Biohazards

Exposure to microorganisms that grow on wood can also cause potential health effects. Endotoxins from bacteria and allergenic fungi growing on wood are the main biohazards found in wood processing workplaces.

Exposure to these biohazards can cause adverse health effects such as organic dust toxic syndrome (ODTS), bronchitis, asthma, extrinsic allergic alveolitis (EAA), and mucous membrane irritation. The fungi predominantly associated with EAA and ODTS are dry spored species such as Aspergillus and Penicillium.

A study of wood dust exposure conducted in the timber industry in NSW, concluded that woodworkers from the tree felling stage to final manufacturing processes are exposed to airborne wood dust of different particle sizes, concentrations and compositions. Sanding, routing, wood turning, and copy lathing were found to be the main woodworking processes that gave rise to high exposure levels. This study also revealed high prevalence of chronic bronchitis, frequent headaches, eye and throat irritation, and nasal symptoms including regular blocked nose, runny nose and excess nasal secretion, sneezing and sinus problems among woodworkers. The results also showed that exposure to wood dust and biohazards associated with wood dust have negative effects on the lung function of woodworkers. (Alwis et al., 1999)

Medium Density Fibre Boards (MDF)

MDF is widely used in the joinery and furniture industry as well as in building and housing construction. The major constituents of MDF particle boards are pulverized softwood and urea-formaldehyde resin, both of which are recognized as potential health hazards in the working environment. MDF produces very fine dust during processing and the dust particles act as a carrier of absorbed formaldehyde to the lower airways of lungs.

Wood dust and formaldehyde together have been reported to cause respiratory irritation with symptoms of dryness of throat, rhinitis and eye irritation as well as occupational skin disease. Protective measures for wood dust exposure should be followed when MDF is used.

CCA Preservatives in Timber

A preservative known as CCA is used widely to treat timber in both industrial and domestic situations. CCA is a water-borne preservative and contains copper, chromium and arsenic salts dissolved in water. Exposure to CCA is considered as a potential health risk mainly because some arsenic and chromium compounds are known to cause cancer.

The main health risk from CCA timber preservation is to those workers who use CCA to treat the timber. More information on timber preservatives is available through the National Occupational Health and Safety Commission (NOHSC) in their National Code of Practice for the Safe Handling of Timber Preservatives and Treated Timber (NOHSC, 1989) and the Guidance Note for the Safe Handling of Timber Preservatives and Treated Timber.

Is CCA-treated timber a health risk?

The pressure treatment process used in CCA preservation results in a high degree of fixation by the timber. This means that it is unlikely that any of the chemicals in CCA (arsenic or chromium salts) would leach out from the treated timber. The main concern is for exposure of workers who are using the product to do the initial treatment of the timber.

There are few studies of occupational exposure to CCA in timber treatment and its processing. They show few significant health effects associated with CCA exposure except for some cases of dermatitis. However, some arsenic and chromium compounds used in CCA are toxic (poisons) and a number of short-term effects including respiratory problems can also occur from inhalation of arsenic dust or chromium salts.

The known health effects are from the various chemical components in CCA and not from the treated timber. Therefore, potential health risks from CCA-treated timber would be limited to situations when high amounts of dust may be generated from the sawing or grinding of the timber. Suitable exhaust ventilation or personal protection must be provided in such instances.

It is recommended practice that freshly treated timber is stored at the treatment plant for at least two weeks (and up to 6 weeks) to ensure fixation and surface drying of the CCA.

Timber for domestic or playground use should also be surface washed prior to distribution.Do not burn CCA-treated timber when barbecuing or building fires because harmful products can be released.

Controlling wood dust

In ensuring that the potential health hazards associated with timber work and wood dust are controlled, employers should:

  • Ensure that workers are made aware of the potential health effects of wood dust exposure.
  • Provide good housekeeping to ensure that excessive amounts of dust do not accumulate inside equipment and in work areas, as this can cause fire or explosion hazards.
  • Provide effective and adequate exhaust ventilation systems for all the machinery and hand-held tools. Dusty processes should be segregated.
  • Although it is difficult to control dust completely, it is usually possible to control the levels to within safe occupational limits with a well designed, efficient and properly used exhaust ventilation system. Such a system must be regularly maintained. Where this is not possible, suitable respiratory protection equipment should be provided for all workers.
  • Defective old machinery (especially in sawmills) should not be operated.
  • Compressed air jets should not be used to remove laden dust from machinery and surfaces, as it makes dust airborne. Dusty surfaces and machinery should be cleaned regularly using a dustless technique such as vacuum cleaning.
  • Workers should be trained regarding the use and maintenance of ventilation systems and also the use and maintenance of personal protective equipment.

Occupational exposure standards for wood dust

The National Occupational Health and Safety Commission in the Exposure standards for atmospheric contaminants in the occupational environment outline the following standard of 1 mg/m3 for hardwood and 5 mg/m3 softwood dust exposure per an 8 hour Time Weighted Average.

This Fact Sheet is courtesy of The Workers Health Centre.

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