Dust: The Hidden Enemy

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This article is from Issue 5 of Woodcraft Magazine.

Shop safety doesn’t always involve the obvious issues of cutting tools, equipment guards and eye protection. Silent and often invisible, wood dust is a hazard every woodworker should strive to control.  

By John English

I gave up smoking in 1984 and for a decade thereafter congratulated myself on saving my lungs. Then I got involved in setting up a wood products facility and was asked to discover how to control dust. In the course of my research, I began to understand that smoking wasn’t the only risk to which my lungs had been exposed over the years. 

While woodworkers have always been aware of dust as an irritant, we’re just now beginning to understand exactly how harmful it can be. And while some of us don’t work every day in a dusty environment, we may still be at a lot higher risk that we think. 

People over 50 – especially smokers and ex-smokers – who spend two days a week or more in their shops are apparently just as susceptible to health problems as professional, full-time wood industry workers. And here’s the frightening bit: They may even be at higher risk. 

One of the comments I heard over and over while researching this article was that, thanks to federal legislation over the past two decades, pro shops nowadays are often a whole lot healthier places than the average hobby shop. Water-based contact adhesives and finishes have contributed to the cleanup, but so have improved dust collection at the machines, systemic air scrubbers and personal protective gear in general.

DEFINING THE PROBLEM 

Size really does matter after all. The smaller the waste particles you generate, the higher the health risk. Every cubic foot of air in your shop plays host to tens of thousands of tiny airborne particles. The most common of these are biological (pollens, plant spores, molds, viruses and bacteria), and mechanical (sanding dust and the like). While your eye can see dust floating in the sunshine of a shop window, those visible particles are all at least 10 microns in diameter. A micron measures just .00003937 of an inch, and the problem is that 99 percent of the damaging dust particles in your shop’s air are less than a single micron in size. They are utterly invisible.

To understand what all this means, we need only look a bit north – Canada has been wrestling with the issue for years. Canada’s Alberta Department of Human Resources and Employment in Edmonton has had a long history of dealing with the woodworking and forestry industries. Consequently, their “Workplace Health and Safety Bulletin #CH045” contains a great deal of information on the hazards of working with wood. The following is reprinted with permission.

“The health effects of exposure to wood dust are due to chemicals in the wood or chemical substances in the wood created by bacteria, fungi, or moulds. Coughing or sneezing is caused by the dust itself. Dermatitis and asthma may be due to sensitivities to chemicals found in the wood. Plicatic acid, for example, found naturally in western red cedar, is responsible for asthma reactions and allergic effects associated with the wood.

“Respiratory system effects due to wood dust exposure include decreased lung capacity and allergic reactions in the lungs. Two types of allergic reaction can take place in the lungs: hypersensitivity pneumonitis (inflammation of the walls of the air sacs and small airways) and occupational asthma.”

Jet’s 1½-hP model 1100CK dust collector has incorporated improved canister technology. With higher efficiency than typical fabric collector bags, the canisters can trap dust particles as small as 2 microns.

Further Concerns

While decreased lung capacity, dermatitis and asthma can certainly wreck your day, the real story behind wood dust seems to be its carcinogenic properties. It can take up to 20 years for the first signs of dust-related cancer to appear. The International Agency for Research on Cancer has classified wood dust as a carcinogen – a cancer-causing substance. The most common form of the disease among woodworkers is perhaps surprising – you might think lung cancer, but that’s not so. There is a large body of evidence stating that the primary risk is nasal cancer; in particular, a form called adenocarcinoma. Again, we can refer to the Alberta bulletin:

“The highest risks appear to be to those workers exposed to hardwood dusts, most commonly beech and oak. Many of the studies looked at workers exposed in the 1940s and 1950s (the cancer can take more than 20 years to develop), and most of the exposure levels were much higher than those seen in today’s industry. Most of the studies looked at workers who were exposed to unspecified types or mixtures of wood dust.”

Brian Kohler is the national representative for health, safety and environmental issues for Canada’s Communications, Energy and Paperworkers Union, a trade union representing workers in that country’s woodworking industry. In 1995, Brian wrote a report on the dangers of woodshop dust. Among the dangers he documented were some not directly emanating from hardwood.

“Wood dust may also contain other contaminants,” he wrote. “For example, if the dust results from the sanding or shaping of particleboard, it is likely to contain some of the amino resins (e.g. urea-formaldehyde, phenol-formaldehyde, melamine-formaldehyde) that are used to bond the particles together. Dust from preserved lumber (treated lumber) may contain chemicals such as copper naphthenate or pentachlorophenol.”

While great strides have been made recently in the safety of pressure-treated lumber and plywood, there are still large stocks of older materials in shops across the country that contain the chemicals Kohler mentions. 

“Of particular concern when handling wood dust,” he continues, “is the possibility of a dust explosion. This danger increases as the particle size is reduced. A recent discussion … proposed that a flammable dust be considered an explosion hazard if more than 5 percent of the particles had a size of less than 500 microns. Wood dust has been the cause of many spectacular explosions in the past.”

If you have an existing dust collection system in your shop, or are about to install one, it must be grounded. Metal ductwork can be grounded rather easily, but plastic hoses should have a metal wire running through them which is attached to a grounding rod or the building’s ground system. There has been serious debate on the effectiveness of such grounding, however, so consult your electrician for details.

FINDING SOLUTIONS

Now that we’re all thoroughly depressed by the risks involved in working in a dust-polluted environment, let’s take a look at a much more encouraging aspect of the problem. Over the past 50 years, the timber, millwork and furniture industries (with federal oversight) have all paid a great deal of attention to the hazards of dust, and they have developed numerous strategies to combat the risks. Most of their solutions are applicable to hobbyist and small professional shops. It’s just a matter of scale.

The one reality that emerges from all the research available is that nuisance masks – those cheap, paper masks sold in bulk – are essentially useless, and a waste of both time and money. If you have a beard, they leak. If you have a large nose, or a small chin, or wear eyeglasses or protective goggles, they are more of a nuisance than the dust. In fact, the false sense of comfort they imbue can actually cause people to ignore the dangers involved and refrain from taking other, more effective steps in dust control.

Without exception, all of the experts agree that the best way to reduce risk is to eliminate dust at its source by attaching a collection device to every shop tool or machine that generates waste. “As for any hazard,” Kohler says, “control at or near the source through engineering design is preferred to general measures or personal protective equipment.”

But, as most of us have discovered, even the most assiduous efforts in this area won’t solve 100 percent of the problem – there are always a few spots that you just can’t seal up. Take, for example, the difficulties involved in sealing up a radial arm saw. So we can’t just rely on the dust collector.

Ambient air cleaners can pick up the tiny airborne particles your main dust collection system misses. Delta’s model 50-875 (left) is one of the highest-airflow three-speed air cleaners in its class. It filters at 540, 730 or 1,200 cfm of air to effectively filter a 20' x 20' x 8' workshop 13, 16 or 18 times per hour. The standard 1-micron inner pleated filter and electrostatic outer filter will trap 99 percent of dust particles 1 micron and larger. For smaller shops or when portability is needed, a movable unit like Shop-Vac’s air cleaner (below) weighs only 15 lbs., and catches dust particles 5 microns and larger. It can move 235 cfm of air to filter a 290 sq. ft. shop about every 10 minutes.

AIR CLEANERS AND SCRUBBERS

The second level of defense is to remove all the airborne dust particles that have escaped the collector. The most effective (and least expensive) way to do that is to buy or build a shop air cleaner. This is basically a box full of filters with a fan, which can mount to a wall or hang from the ceiling, or is a freestanding floor model. While there are numerous filters on the market that will capture particles of 2 microns or larger, very few can eliminate smaller miscreants. To do that, you need an air scrubber (usually one with an electrostatically charged filter) that collects debris of 1 micron in size, or even smaller.  

There are several shop air cleaners on the market, running from about $200 all the way into the thousands. Almost all of them follow the same design guidelines – a motor-driven fan pulls contaminated air from the shop, feeds it through a series of filters from coarse to fine, then returns it to the work area. In most models, both fan and filters are housed in a ceiling- or wall-mounted box, a design feature that takes advantage of gravity to create a cycle of air within the workspace. This means that the air is always in motion, and each cubic foot is subject to several trips through the filters every hour. 

Sizing the air cleaner for your shop is a simple mathematical process. Start by working out how many cubic feet of air your shop holds by multiplying the length by width by height. For example, a 20' x 20' room with an 8' high ceiling will hold 3,200 cu. ft. of air.

The recommended number of times that the air should be filtered each hour varies, but most experts agree on a number between four and eight. If we settle for six, we then need to have a fan that will move six times the room’s volume each hour. In our example above, that’s 3,200 times 6, or 19,200 cu. ft. per hour. As most fans are rated in cubic feet per minute (CFM), we need to divide the result by 60 to decide what size fan we need. In the example, we would need a fan that moves 320 CFM. 

After researching the units available, you may well discover that you need two or more scrubbers, depending on the size of your shop. If you do, place them over the areas where the most dust is being generated, such as a table saw or a sanding station.

The ultimate in dust protection for you might be a powered respirator. There are a number of new models on the market. From left: The Aircap 2 has a familiar ball-cap design, and filters up to 6 cfm; Triton’s power respirator includes hearing protection and filters up to 5.3 cfm; the Trend Airshield resembles a catcher’s mask, and filters up to 6.36 cfm. All three units are battery powered; the Aircap 2 and Triton use belt-mounted power packs, while the Trend power supply is self-contained.

Although not the most efficient system in the world – especially for woodworkers with beards or mustaches – it’s hard to beat the simplicity and availability of an inexpensive dust mask.

PERSONAL PROTECTION

While nuisance masks are inappropriate for fine wood dust, there are several masks and other devices available which can dramatically reduce one’s exposure to the risks involved in activities like sanding or turning. The best of these are integrated systems that include a face shield, a powered respirator, and sometimes a helmet. Systems that pump fresh air into the respirator are known as positive-pressure systems.

While powered respirators are definitely the best option, there are less cumbersome ways to tackle the problem, too. Paint and spray booth masks, known as negative-pressure systems, are a huge upgrade from nuisance masks. Most of them are designed to handle vapors as well as dust, so they can protect you during the finishing of your projects, too. They generally are equipped with a pair of disposable canister filters and have to meet stringent standards set by NIOSH, the National Institute for Occupational Safety and Health. The filters (and usually a couple of prefilters, too) are replaced when breathing becomes uncomfortable due to clogging. The mask is usually made from either silicone (softer) or neoprene (more resistant to chemicals), and it does a much better job of conforming to one’s face than any disposable. However, those of us with facial hair are out of luck – most of them won’t seal around a beard. For that, you need a powered respirator … or a shave.

The bottom line is that dust is an irritant. As such, it can cause numerous health problems including cancer, dermatitis, allergies and even a life-threatening anaphylactic (allergic) reaction. Merely treating its symptoms is not a healthy way to go. You need to treat the cause and remove the dust from your shop, skin, lungs and life.

GO TO THE DUST

Collecting dust at the source can sometimes be tough, especially for portable machines, but new products are addressing the issue. The Loc-Line series of rigid but flexible ducting – combined with a variety of pickup nozzles for different tasks – allows for pinpoint dust grabbing.

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