Sawdust (or wood dust) is a by-product or waste product of woodworking operations such as sawing, sanding, milling and routing. It is composed of very small chips of wood. These operations can be performed by woodworking machinery, portable power tools or by use of hand tools. In some manufacturing industries it can be a significant fire hazard and source of occupational dust exposure.
Sawdust, as particulates, is the main component of particleboard. Its health hazards is a research subject in the field of occupational safety and health, and study of ventilation happens in indoor air quality engineering. Sawdust is an IARC group 1 Carcinogen. Wood dust can cause cancer. Frequent exposure to wood dust can cause cancers of the nose, throat, and sinuses.
Exposure to wood dust can result in coughing, sneezing, irritation, shortness of breath, dryness and sore throat, rhinitis, conjunctivitis, dermatitis, allergic contact dermatitis, decreased lung capacity, asthma, hypersensitivity pneumonitis, headaches, chills, sweating, nausea, cramps, loss of weight, giddiness and irregular heartbeat.
Formation Two waste products, dust and chips, form at the working surface during woodworking operations such as sawing, milling and sanding. These operations both shatter lignified wood cells and break out whole cells and groups of cells. Shattering of wood cells creates dust, while breaking out of whole groups of wood cells creates chips. The more cell-shattering that occurs, the finer the dust particles that are produced. For example, sawing and milling are mixed cell shattering and chip forming processes, whereas sanding is almost exclusively cell shattering.IARC 1995. Wood Dust. In IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol. 62: Wood Dust and Formaldehyde. Lyon, France: World Health Organization International Agency for Research on Cancer, p. 70.
Types Sawdust takes its characteristics from the species of tree and the tool used to create it. Understanding this is important for effectiveness and safety.
Hardwood vs. softwood Sawdust from hardwoods is denser and more fibrous; it can be made from trees such as oak, maple, walnut, and cherry. It is used for smoking meats, mushroom cultivation, and heavy-duty floor-sweeping compounds.
On the other hand, sawdust from softwoods is resinous (oily) and lighter in weight; it can be sourced from pine, cedar, and fir. It is best used for animal bedding and fuel pellets. Cedar sawdust is popular for its pleasant scent and natural insect-repelling properties. The resins in softwood sawdust make it more flammable than hardwood sawdust.
Uses A major use of sawdust is for particleboard; coarse sawdust may be used for wood pulp. Sawdust has a variety of other practical uses, including serving as a mulch, as an alternative to clay cat litter, or as a fuel. Until the advent of refrigeration, it was often used in icehouses to keep ice frozen during the summer. It has been used in artistic displays, and as scatter in miniature railroad and other models. It is also sometimes used to soak up liquid spills, allowing the spill to be easily collected or swept aside. As such, it was formerly common on barroom floors.Felman, David (2005) "Why Did Bars Used to Put Sawdust on the Floor? Why Don't They Anymore?" Do Elephants Jump? HarperCollins, New York, page 118, , quoting Christopher Halleron, bartender and beer columnist. It is used to make Cutler's resin. Mixed with water and frozen, it forms pykrete, a slow-melting, much stronger form of ice.
Sawdust is used in the manufacture of charcoal briquettes. The claim for invention of the first commercial charcoal briquettes goes to Henry Ford who created them from the wood scraps and sawdust produced by his automobile factory.Green, Harvey (2006) Wood: Craft, Culture, History Penguin Books, New York, page 403,
Research has examined also the use of wood shavings as a partial volume replacement for fine aggregates in cement mortar.
Food
Cellulose, fibre starch that is indigestible to humans, and a filler in some low calorie foods, can be and is made from sawdust, as well as from other plant sources. While there is no documentationPacking houses formerly purchased large quantities of sawdust for the cutting room floors, and still purchase sawdust for use as a fuel and flavoring in the smoking process. for the persistent rumor, based upon Upton Sinclair's novel The Jungle, that sawdust was used as a filler in sausage, cellulose derived from sawdust was and is used for sausage casings. Sawdust-derived cellulose has also been used as a filler in bread.
When cereals were scarce, sawdust was sometimes an ingredient in kommissbrot. Auschwitz concentration camp survivor, Dr. Miklós Nyiszli, reports in Auschwitz: A Doctor's Eyewitness Account that the subaltern medical staff, who served Dr. Josef Mengele, subsisted on "bread made from wild chestnuts sprinkled with sawdust".
Health hazards
Airborne sawdust and sawdust accumulations present a number of health and safety hazards. Sanding, routing, shaping and cutting of wood releases wood particles into the air. They become airborne and inhaled. Wood dust can also land on surfaces such as tables and floors and become airborne again when disturbed. Handling of wood chip mulch and compost, especially when dry, can result in wood dust being inhaled, too.
The dust itself causes coughing, sneezing or irritation. Shortness of breath, dryness and sore throat, runny nose (rhinitis), and inflammation of the eye's mucous membranes (conjunctivitis) may also present. Dermatitis with dry, itchy, red, or blister skin is common. It may be due to chemicals' presence in the wood. Allergic contact dermatitis is also possible.
Effects of the respiratory system include "decreased lung capacity, and allergic reactions in the lungs such as hypersensitivity pneumonitis (inflammation of the walls of the air sacs and small airways), and occupational asthma. Hypersensitivity pneumonitis may develop within hours or days following exposure and is often confused with cold or flu symptoms because it begins with headaches, chills, sweating, nausea, breathlessness, etc. Tightness of the chest and breathlessness can be severe" and get worse if exposure continues. The moulds that grow on the wood may also cause some of the hypersensitivity pneumonitis conditions. "Western red cedar is a wood that has a clear association with the development of asthma." Different species of wood have different toxic effects. The chemicals may enter the body through the skin, lungs, or digestive system and may cause breathlessness, headaches, cramps, loss of weight, giddiness and irregular heartbeat.
Many trees species have been associated with health effects, some of them include alder (common, black, red), beech, birch, cedar (western red), douglas fir, fir (grand, balsam, silver, alpine), hemlock, Larch (European), mahogany, maple, oak, pine (white, lodgepole, jack), poplar, rosewood, spruce, teak, walnut (black) and yew.
Other products used in or on wood may also have hazards, some examples include pesticides, resins, paint, paint strippers, adhesives, glues, waterproofing compounds, lacquers, varnishes, sealants and dyes.
Wood dust is a known human carcinogen. It can cause cancers of the nose, throat, and sinuses. Certain woods and their dust contain toxins that can produce severe allergic reactions. The composition of sawdust depends on the material it comes from (e.g., natural wood, processed wood or wood veneer).
Breathing airborne wood dust may cause allergic respiratory symptoms, mucosal and non-allergic respiratory symptoms, and cancer.United States Department of Labor: Occupational Safety and Health Administration. Wood Dust. In the US, lists of carcinogenic factors are published by the American Conference of Governmental Industrial Hygienists (ACGIH), the Occupational Safety and Health Administration (OSHA), and the National Institute for Occupational Safety and Health (NIOSH). All these organisations recognize wood dust as carcinogenic in relation to the nasal cavities and paranasal sinuses.
People can be exposed to wood dust in the workplace by breathing it in, skin contact, or eye contact. The OSHA has set the legal limit (permissible exposure limit) for wood dust exposure in the workplace as 15 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an 8-hour workday. The NIOSH has set a recommended exposure limit (REL) of 1 mg/m3 over an 8-hour workday.
To reduce exposure, indoor dust-collection or air-filtration system can be installed. A sanding table or saw hood that draws particles downward can also be used. Blowers, fans, brooms, or compressed air should not be used to move the dust. Vacuum with a HEPA filter, use wet cloths for clean-up, seal and dispose wood dust with care from vacuum or other dust extraction systems, and "Change out of clothes that contain wood dust before entering your home, car, or other areas" are also important for reducing exposure.
Water-borne bacteria digest organic material in leachate, but use up much of the available oxygen. This high biochemical oxygen demand can suffocate fish and other organisms. There is an equally detrimental effect on beneficial bacteria, so it is not at all advisable to use sawdust within home aquariums, as was once done by hobbyists seeking to save some expense on activated carbon.
Explosions and fire
Sawdust is flammable and accumulations provide a ready source of fuel. Airborne sawdust can be ignited by sparks or even heat accumulation and result in dust fire or explosions.
Environmental effects At sawmills, unless reprocessed into particleboard, burned in a sawdust burner, or used to make heat for other milling operations, sawdust may collect in piles and add harmful leachates into local water systems, creating an environmental hazard. This has placed small sawyers and environmental agencies in a deadlock.
Questions about the science behind the determination of sawdust being an environmental hazard remain for sawmill operators (though this is mainly with finer particles), who compare wood residuals to dead trees in a forest. Technical advisors have reviewed some of the environmental studies, but say most lack standardized methodology or evidence of a direct impact on wildlife. They do not take into account large drainage areas, so the amount of material that is getting into the water from the site in relation to the total drainage area is minuscule.
Other scientists have a different view, saying the "dilution is the solution to pollution" argument is no longer accepted in environmental science. The decomposition of a tree in a forest is similar to the impact of sawdust, but the difference is of scale. Sawmills may be storing thousands of cubic metres of wood residues in one place, so the issue becomes one of concentration.
Of larger concern are substances such as lignins and fatty acids that protect trees from predators while they are alive, but can leach into water and poison wildlife. Those types of things remain in the tree and, as the tree decays, they slowly are broken down. But when sawyers are processing a large volume of wood and large concentrations of these materials permeate into the runoff, the toxicity they cause is harmful to a broad range of organisms.canadiangeographic.ca, Canadian Geographic Online
Wood flour
Wood flour is finely pulverized wood that has a consistency fairly equal to sand or sawdust, but can vary considerably, with particles ranging in dimensions from a fine powder to roughly that of a grain of rice. Most wood flour manufacturers are able to create batches of wood flour that have the same consistency throughout. All high quality wood flour is made from hardwoods because of its durability and strength. Very low grade wood flour is occasionally made from sapless softwoods such as pine or fir.
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