Woodworking comprises a broad range of applications that generate particulate (such as wood chips, sawmill shavings) and dust fines from wood material processing. Planing, sawing, routing (shaping), milling, sanding and lathe turning are used in countless commercial and industrial facilities, professional trade and educational institutions. Local exhaust ventilation (LEV) should match each process with prime consideration given to the combustible nature of wood particulate.
Common Processes / Sources And Hazards
Material composition - Processing method
Wood dust contaminants vary as a function of the material species, their composition, and the method used to generate the dust, which we may identify as a source. Understanding each process is the key to the identification of different sources. This can foster the development of new or revised techniques that reduce the number or size of sources, and contaminant clouds.
Airborne contaminant clouds - Dust-laden surfaces
For example, local exhaust ventilation (LEV) hood design should match the process, that is, cover each wood cutting, shaping and sanding operation with suitable air flow to extract contaminant-laden air, otherwise the hoods do not empty as fast as they are filled. In other situations, compressed air used to clean contaminated clothes, surfaces or components produce airborne contaminant clouds that are difficult to control, let alone capture. Also, hand sanding, bagged material stacking and wood panel loading on dust-laden surfaces not only contaminate worker clothing, but generate dust clouds. These situations illustrate the need to better understand the processes that underlie wood dust generation and their propagation to the surrounding environment.
Hardwoods - Softwoods - Particle boards - MDF
Material construction is critical. For example, hardwoods (deciduous trees such as birch, aspen and maple) produce finer particulate compared to softwoods (conifers such as Douglas fir, spruce, pine and cedar). Particle board (also known as chipboard, medium density fiberboard or MDF) contains wood chips, particles or flakes together with a resin or a glue. It may be an ideal candidate for panel construction; nonetheless, it represents a serious health hazard for workers. Indeed, the fine dust released during sawing often contains formaldehyde, a frequently-used ingredient in resin and a recognized human carcinogen. Other than the toxicity of formaldehyde-based resins, exposure to inhalable dusts from sawing / sanding MDF in cabinet-making workshops is dependent on operator proximity to the source as well as particle size, the coarser fraction exhibiting the more significant dust loading.
Prolonged or repeated exposure and inhalation of wood dusts has short and long term effects on worker health. Depending on the species, wood dust contains a variety of biologically active, low molecular weight compounds (such as alcohols, terpenes). Wood dust is a human carcinogen, with a clear relationship between cancers of the nasal cavities and high levels of wood dust exposure, particularly from hardwood species. Other adverse health effects of wood dust exposure include irritation of the eyes, nose and throat from short term exposure to dust. Decreased lung function, increased respiratory symptoms and allergic reactions are also associated with wood dust exposure. This may lead, if untreated, to occupational asthma and other lung diseases.
In Canada, federal and provincial regulations have established occupational exposure limits (OEL) for workers. ACGIH have set Threshold Limit Value (TLV) occupational exposure guidelines for the industry in the USA. In England, HSG 258 provides guidance for suppliers / users to help identify sources of exposure, offers assistance to provide LEVs that are fit for their intended purpose, are shown to work and continue to be effective.
The IRSST (Quebec), NIOSH (USA) and research affiliates in England, France and Germany provide concerted guidance to promote worker health and safety in industry.
Control of fire / explosion hazards
Wood dust, for the most part, is combustible and explosive. The dust explosions may be triggered by many sources such as a spark, static electricity, friction or glowing materials. Typically, the first or primary explosion disturbs built-up combustible dust on surrounding surfaces. Then this dust ignites in a secondary explosion often more powerful and devastating than the initial explosion. To minimize the risk of fire, explosion, loss of life or damage to property, dust collection systems require sprinklers and explosion-proof devices / venting in accordance with the ATEX 2014/34/EU equipment directive (Europe), or the HAZLOC (North America) standard and the NFPA 664 code.
Dust collector design
For effective capture, duct velocities should range from 15 m/s for light density dust (sawdust) to 20 m/s for wood shavings.
Dust collection solutions may require special options or accessories to improve their safety and reliability. Cyclone collectors are appropriate when used as the primary filter for large particulate or as a pre-filter in cartridge collectors that handle a wide range of particulate matter. Most production woodworking applications would benefit from properly configured cartridge dust collectors and baghouses. Shaker baghouse dust collectors are well-suited for general, occasional woodworking operations such as found in trade schools.
When handling combustible dust, we recommend that dust collection units be located outdoors and protected pursuant to NFPA regulations and where necessary with chemically treated fire retardant cartridge filters. Wide-pleated filters satisfy the needs of processes generating large particulate.
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