Although small amounts of fine wood powder are produced during most wood machine operations, powder is primarily created when you sand wood. Whether you deposit a thin layer of powder on the bench or create a cloud of woody effluent, is greatly influenced by your means of sanding.

Fine wood dust is composed of particles that are really broken pieces of wood fibre abraded from the side, face or end grain of a board. Think of each particle as a tiny chip that's been scraped off by an abrasive particle (sandpaper) as its scores the surface of the workpiece. Generally speaking, the finer the grit sandpaper you use, the finer the abrasive particles and the finer the size of the dust particles produced.

Very fine dust is Measured in Micron's, one Micron = 1000th of a mm. Large dust particles, 100 Micron's and bigger, tend to fall to the ground quickly. In contrast, wood powder can be so fine, that particles are easily suspended in the air where they waft around for a long time. A 5 micron particle stays aloft for 30 minutes or longer, depending on the amount of air movement in the shop.

The lightness of the particles explain why you can run a power sander over a large panel, blow or brush the top clean, and then come back half an hour later and find a thin layer of fine powder recoating everything. If you don't keep the floors and benches tidy, just picking up a board or walking around the shop can raise a dusty cloud. Even the act of tidying up with a broom and dustpan can stir the dust up. This fine dust also makes it difficult to do any kind finishing in the same space that you make sawdust; particles continue to settle as the finish dries and you end up with a nubbly surface.

Fine dust easily floats under doorways and through ventilation ducts, to infiltrate spaces adjacent to your workshop, such as your office, finishing booth or, if your shop is attached to your house, your living room. This dust also clings to your clothing and travels indoors whenever you run in for a cold drink in the middle of a work session.

The good news is that it is much easier to catch and collect fine wood dust than it is to corral large chips or shavings. The air velocity produced by most shop vacuums is sufficient to collect the dust produced by portable power tools that have ports for connecting the dust bag or vacuum hose. Dust production during handsanding operations can be mitigated by the use of shop ventilation or an air filtration device.

Capturing the dust produced by a large drum sander with a central collection system isn't much of a problem, provided that the hood that directs the flow of air to capture the dust particles is well designed.

The bad news is that the fine dust that isn't captured can present the most serious hazards to the woodworking: an assault on respiratory health. Ironically, its the smaller dust particles, 10 Micron's and less that create respiratory problems that range from mildly annoying to life-threatening.

In addition to the harmful effects of the dust particles themselves, woodworkers can also be negatively affected by certain soluble chemical components carried in or along with the wood dust. These chemicals include a whole gamut of resins and extractives, commonly found in (but not limited to) exotic species of hardwoods. Extractives serve a living tree by repelling insect attacks and retarding the decay of the tree's non living heartwood. Wood dust carrying extractives can exacerbate the effects of the fine dust particles themselves or cause allergic reactions in woodworkers who are sensitive to the extractives chemical makeup (sometimes after only limited contact). These chemicals include natural components with frightening sounding names, such as alkaloids, glycosides, saponins and quinones. Wood species with extractives that are more prone to cause allergic reactions include redwood, mahogany, boxwood, western red cedar, yew, satinwood, teak, ebony and wenge. Western red cedar is one of the most infamous of these species, because it contains an allergen called plicatic acid that causes a condition commonly known as red cedar asthma.

Another possible source of allergic reactions from wood dust are the spores of fungus that can be contained in the dust. Certain funguses cause decorative staining in woods, known as spalting. Even fungus occurring in the bark of a tree can cause allergic reactions. A condition known as maple bark disease is ostensibly caused by the fungal spores found in the maple bark, which are released when the wood is cut or when maple burls are turned on the lathe.

As well as potentially harmful effects of the natural compounds found in wood, there is also the danger of being exposed to the dust from adhesives used in woodworking. These include glues used to manufacture wood based materials, such as particle board and plywood, and glues used to make parts of assembly projects. Some of these adhesives such as polyurethane glue, contain compounds such as isocyanates, which can cause severe reactions in some people. Working with recycled wood (from old houses and barns) can also present health problems. Surfaces may have once been coated with lead based paints or treated with wood preservatives, which typically contain toxic substances, such as pentachlorophenol and copper napthenate (known commercially as copper green). Pressure treated timber has also been impregnated with these kinds of preservatives. When you cut, plane, shape or sand wood, you create dust that can carry these substances into your lungs, where they are subsequently absorbed into your bloodstream.

Severe symptoms from exposure to wood dust may include: Click here

Just as with the respiratory problems from fine dust particles themselves, what makes the breathing of other chemicals carried by wood dust such an insidious problem is that the symptoms don't always manifest themselves quickly. Unless you develop an allergic reaction that suddenly alert's you to a wood dust related health problem, symptoms may take years or even decades to appear. As with most serious health problems, its always more difficult to overcome a problem once the body has experienced chronic damage.

This is yet another good reason to evaluate your dust control needs carefully, so that your not trading your future and the future of your employees good health for the enjoyment (and income, if woodworking is your vocation) you get from a lifetime of woodworking.

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Most woodworkers who have installed dust collection in their shops, be it a small shop vacuum or a large central collection system, rest easy thinking they have got sawdust beat. But usually there is still and invisible culprit lurking in the shop: the wood powder with particles so small that it can pass right through filters on some vacuums and the fabric used in some central collection bags. Like demon seeds ready to unleash contagion, these diminutive dust particles a so light that they can travel around on the air itself, held aloft by static electricity or circulating air current. You can barely see them under ordinary lighting, but they are there, remaining airborne for hours after the last board has been sanded. If you have any doubts, shut the lights off in your shop some evening after a sanding session, and then shine the concentrated beam of a flashlight across the shop; the light will reveal a swirling swarm of talcum powder like dust. The phenomenon is known as the Tyndall effect; your have seen it in the movie theater when dust or smoke passes in front of the projection beam. What's more insidious, the smallest of these particles are invisible to the eye yet the most harmful to your lungs.

How small are the fine dust particles that can harm us?

Particles between 10 and 20 microns (we can't even see individual particles smaller than 100 microns; that's 1/10 of a millimeter) tend to become trapped in the outer passages of your respiratory system (resulting in the grotty goo that you see on a clean hanky when you blow your nose after a sanding session. Minute wood particles, particularly those between 0.3 microns and 10 microns easily penetrate deep into the farthest reaches of your lungs, even into the tiny air sacs called alveoli. Really tiny particles (under 0.3 microns a small enough to be expelled by exhalation.

How fine dust hurts your lungs

because we breathe in a certain amount of dust in our everyday lives, our bodies have built in protection mechanisms, as depicted in the drawing below.

These respiratory defenses include nasal hairs, which snag large particles as you inhale; the mucus, a sticky blanket that lines your respiratory track and acts like flypaper to capture errant dust particles; and the cilia, which are tiny hairs that line your respiratory track. Like the tentacles of a sea anemone, the cilia works to transport dust particles trapped in the mucus (using a breathing motion that takes place about 10 times per second) and moves them toward the back of your throat where they can be swallowed or coughed up. The cough reflex is a protective reaction that works to expel the mucus and dust that can build up in the respiratory system.

Finally there are the alveolar macrophages, which serve to clean out dust that gets into your lungs' alveolar sacs.

Minute dust particles harm us by interfering with the lungs' functions in a variety of ways. As large quantities of dust particles become lodged in the lungs, they tend to foul the dust ejection systems previously described.

First, large amounts of dust clog the natural cleaning action of the lungs' cilia, which leads to irritation. As the cilia becomes more clogged, their effectiveness is reduced, so the lungs lose capacity to eject dust. Eventually, chronic exposure can leave permanent damage of the lungs' tissue, which can result in the buildup of scar tissue.

By restricting the absorption of oxygen to the blood, chronic exposure to fine dust can lead to shortness of breath and dizziness. Further, the effects of dust can weaken the bodies natural defense mechanisms, making you more susceptible to bacterial and viral infections and illness. The result of long periods of exposure to fine wood powder are very similar to cold and flu symptoms and typically include coughing, sneezing, bronchial inflammation, shortness of breath and a runny nose as a result of increases in discharge of saliva and phlegm from the respiratory passages. The kind of lung problems that sometimes development in woodworkers from chronic inhalation of wood dust are similar to those developed by longtime smokers: chronic bronchitis and emphysema. Worse, chronic exposure to wood dust may cause lung cancer (the international agency for research on cancer has classified wood dust as a group one carcinogen).

Another kind of health problem that can be directly linked to exposure to fine wood powder is nose cancer ("nasal adenocarcinoma" in medical vernacular). Woodworkers are about 1000 times more likely to develop nose cancer than non woodworkers (although only one out of every 1500 active woodworkers will ever have to deal with this horror). As with the respiratory problems described previously, nasal cancer tends to develop over many years, sometimes with decades between initial exposure and outbreak of symptoms.

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A recently published study by the International Agency for Research on Cancer (IARC) cities more than 350 case studies to back its claims that wood dust is carcinogenic to humans.

For more than 30 years scientists have argued their case and now, the IARC claims to have the evidence to prove the correlation between breathing in wood dust a a rare type of adenocarcinoma involving the nasal and paranasal sinuses.

The IARC was established by the World Health Organisation in 1965 with a mission to coordinate and conduct research on the causes of human cancer, and to develop scientific strategies for cancer control. Volume 62 of these monographs deals specifically with wood dust and formaldehyde.

A carcinogenicity ranking was developed based on the valuations produced by research groups. These rankings were given as:

Group1 - The agent (mixture) is carcinogenic to humans. The exposure circumstance entails exposures that are carcinogenic to humans.

Group2A - The agent (mixture) is probably carcinogenic to humans. The exposure circumstance entails exposures that are probably carcinogenic to humans.

Group2B - The agent (mixture) is possibly carcinogenic to humans. The exposure circumstance entails exposures that are possibly carcinogenic to humans.

Group3 - The agent (mixture) is not classifiable as to its carcinogenicity to humans.

Group4 - The agent (mixture) is probably not carcinogenic to humans.

Wood dust was given a Group1 rating and formadehyde, Group2A.

Its the fine particles of wood dust inhaled into the nasal passages or lungs which are considered dangerous according to the IARC. At the same time, certain chemical properties inherent in wood, particularly certain hardwoods and western red cedar, make wood dust and allergen.

The IARC targeted operations such as sawing/milling planing, chipping, sanding, routing, shaping, tenoning, moulding and jointing in three phases of woodworking production - rough milling, component making and assembly. These operations all involved the shattering (to a greater or lesser extent) of wood cells, and its from this shattering of the wood that the dust comes. The finer the shattering, the finer the wood dust particles.

Inevitably, sanding is considered the most dangerous of the activities because it almost exclusively produces fine wood dust, and sanding against the grain is likely to produce more dust than sanding with the grain because it causes more wood cells to be shattered. At the same time hardwoods, because their cells are more tightly bound, produce more dust and were therefore found to be more dangerous than softwoods.

The study also looked at wood dust levels by industry - cabinetmaking, office furniture and domestic furniture. Cabinetmaking was found to produce the highest average levels of wood dust. A 1988 study by an American company, Clayton Environmental Consultants, found kitchen cabinet manufacture produced a mean average of 1.6 mg per m3, compared to residential furniture at 0.8mg per m3. This was attributed, in the IARC study, to the fact that wood for kitchen cabinets was usually machined and sanded in the same area of the workshop.

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Wood dust is produced when timber is being worked such as chipping, sawing, sanding, turning, drilling. Sanding id by far the most dangerous as the particles are so fine that a lot of masks do not entirely filter the particles, and, as a result, pass into the nasal cavities, sinuses and lungs.

Hardwoods in general such as beech, oak and mahogany and native hardwoods (eucalyptus) generate fine particles of dust and this has a prime link with nasal cancers. Softwood timber from coniferous tress such as pine, are less of a risk. Medium density fibreboard (MDF) poses another problem due to the bonding agent and should be treated the same as hardwood. A properly designed and maintained exhaust system is the best method of collecting the dust and is the ideal way. However, if this is not practical, dust respirators should be used whenever you are exposed to dust, not only when you are processing your work. The following list of some timbers and the effects that they should have been kept in the workshop.

Compiled from "its safe" by the Construction, Forestry, Mining & Energy Union, National Safety Construction Division (1993)