Toxic WoodsComments (1)
This article is from Issue 47 of Woodcraft Magazine.
Protect yourself from the health issues caused by wood dust and some woods.
While the precautions you take around workshop machinery have served you well and kept your environment accident free, you could be ignoring another hazard that has a way of sneaking up on you, that of so-called toxic woods. Some of your favorite woods have varying levels of toxicity, and people can develop certain unpleasant reactions and symptoms from them. Some are immediate, and some can develop over time. Some are minor, but some can be downright serious.
The reactions stem from chemical compounds in wood that come in contact with the skin, eyes, throat, nose, and respiratory tract, either through direct contact from handling and use or with wood dust serving as the delivery system. I’ll cover some of the species to watch for, the types and severity of reactions, and strategies you can adopt in the shop to minimize health risks and exposure.
The Usual Suspects
It’s difficult to rank the reactions and risks of individual wood species. For just about every wood in use, somebody has reacted to it. In fact, significant, long-term exposure to any wood dust can cause respiratory problems. The OSHA Wood Dust Standard specifies workplace exposure limits for wood dust. The exposure limits are the same for all species, hardwood and softwood, domestic or imported, with one exception. Because of the number of people who have reacted to western red cedar, the allowable exposure limits are half of that allowed for other species. Beyond that point, we depend on history and the experiences of others to identify the troublemakers. The 28 listed at right stand out for the allergic reactions and symptoms they have caused.
It’s a fact that…
Wood toxicity can run within botanic families. In some wood species a particular chemical compound has been identified as the cause of most reactions to that wood. Sometimes that chemical is also found in other, related species. In various “rosewoods,” for example, the Dalbergia species from around the world and some related woods in the same family of trees such as Machaearium scleroxylon, which is sold as Bolivian rosewood, pau ferro, morado, santos rosewood and other market names, have the same chemical that is known to cause reactions. Also related are purpleheart (Peltogyne paniculata), the padauks and sandalwoods (Pterocarpus spp), and wenge (Millettia spp).
Symptoms and Risks
Wood toxicity and the chemicals that cause it divide into several broad, potentially overlapping categories. Here’s the breakdown:
These are chemical substances in wood that irritate exposed areas of the body on some people. Common reactions such as sneezing, coughing, breathing problems, and skin rashes can occur almost immediately, and the severity is proportional to the level of exposure. The symptoms are temporary.
Here, chemical substances in wood can, after repeated exposure, cause the development of an allergic reaction in susceptible individuals. The potential risk depends not just on the wood, but also on the level and frequency of exposure, as well as a person’s sensitivity to developing allergies. Sensitizers are more serious than irritants because of the time delay before symptoms develop, and the escalating severity of the reactions. Over time, they can lead to allergic rhinitis (inflammation of the mucous membrane of the nose), bronchial asthma, and allergic contact dermatitis. The most common wood-related health problem is allergic reactions of the skin (contact dermatitis).
Dangerous and sometimes lethal substances are found in some woods. The potential hazard is usually limited to situations where the manner of use exposes you to an accumulation of the toxin. As with irritants, this can even be a hazard for the person using the wood object, such as a salad bowl or even a wood musical instrument.
Long-term exposure to wood dust can cause cancer of the nasopharynx, which may develop in full-time woodworkers after several decades of steady unprotected contact with fine wood dust. There is also a slightly increased risk for some other serious diseases. Those who work with wood occasionally are far less likely to develop these diseases.
Healthy Shop Strategies
A home woodworking shop needs strategies for reducing exposure to wood dust. Consider the measures below for maximum protection.
Minimize shop dust
First and foremost, do everything possible to collect dust where it’s generated, before it becomes airborne. The primary method for controlling fine wood dust is with localized dust collection directly from the tool itself. This can be in the form of a shop vacuum for benchtop machines and portable power tools to a whole-shop dust-collection system that draws from all the major machines via ductwork and hoses. (See “Small-Shop Dust Collection,” June/July 2009 issue.) Equipped with high-efficiency particulate air (HEPA) 1- to 2-micron filters, such systems not only collect chips, sawdust, and fine dust from heavy makers (the tablesaw, for instance), but they can also cleanse and recirculate the air. Important here is emptying the debris containers and cleaning the filters regularly for maximum efficiency and to prevent dust from recirculating.
Downdraft tables also help contain dust when using portable sanders on smaller parts. Perhaps the cheapest way to maintain clean air is to ventilate the shop with window fans. If you’re fortunate to have a garage shop and pleasant weather, throw open the doors when performing dust-generating work.
Minimize dust inhalation
Cheap and commonly used disposable face masks provide only minimal protection from the inhalation of fine airborne dust. They tend to leak and fog up glasses. For a little more money and better protection (95%), buy tighter fitting reusable masks equipped with an exhale valve (FastCap MXV dust mask, Woodcraft #836875, 10/pkg. $18.99). Respirators with replaceable filters significantly improve protection (99.9%), while offering a still better fit (MSA half-face respirator, Woodcraft #141621, $29.99). However, they can be uncomfortable during prolonged use and in warm weather. Too, both masks and half-face style respirators only keep dust out of your nose and mouth. A full-face style respirator keeps dust out of your eyes as well. Top-end models feature battery-powered filtered air circulation inside the mask, keeping dust off your face, hair, and neck (Trend Airshield Pro, Woodcraft #152709, $409.99).
Minimize skin contact
To minimize contact with troublesome woods and wood dust, you need to protect or reduce exposed skin areas. Wear long sleeves, long pants, hat, face shield, and (when possible to do so safely) gloves, especially when working with reactive woods known to cause dermatitis. Consider disposable coveralls for layered protection.
Play defense with safe practices
Finally, clean yourself and your work area frequently to minimize dust accumulation and exposure. Use a vacuum to collect dust rather than compressed air to blow dust off work surfaces, tools, and clothing. At the end of a woodworking day, change out of your dusty clothes and shoes, and take a shower.
About Our Author
Larry Osborn serves as an wood technology consultant for Woodcraft Magazine. In his day job, he works as a wood science and utilization specialist, as well as a wood anatomy and identification specialist, at the Appalachian Hardwood Center at West Virginia University.
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