In "Getting started with dust collection," we covered the first phase of shop dust collection: controlling large-particle dust, chips and shavings. Your shop will be cleaner and safer, and you'll alleviate some of the health risks associated with wood dust exposure. But even the best dust collection system can still leave clouds of tiny dust particles floating through the air, and these particles pose their own dangers. In this article, we'll look at the drawbacks of letting fine airborne dust run wild and at strategies for handling the problem.
Dust Particle Size and and Respiratory Health
Dust particles are measured in microns, or thousandths of a millimeter. Larger dust particles – greater than 100 microns or so – are heavy enough to fall to the floor quickly. This is the debris that dust collectors are so effective at removing. Fine dust particles, on the other hand, don't have enough mass to fall quickly to the floor and can float through the air in your shop for a surprisingly long time. Once a 5-micron wood dust particle is stirred up, it will stay aloft for 30 minutes or longer, depending on air movement.
Dust particles of less than 10 microns constitute the primary respiratory health risk to woodworkers. They're easily stirred up, stay aloft for a long time and – worse – travel easily into the deepest reaches of the lungs, where they are reported to cause problems ranging from mild allergic reactions to severe and chronic respiratory ailments. More and more woodworkers, convinced by the evidence of health risks, are beginning to take fine wood dust exposure seriously.
Improving the Filter Performance of Your Dust Collector
Dust collectors commonly used in small shop dust collection systems are sometimes called "chip collectors." That's because they really are designed to do their best work at collecting chips, shavings and large dust particles. Many dust collectors are equipped with a filter designed to stop only large particles and let the fine particles associated with respiratory health problems pass through. Because dust collectors move substantial quantities of dust-laden air, a dust collector that lets minute dust particles pass through its filter becomes, in effect, a "dust pump," filling the air around it with clouds of fine dust.
There are a couple of ways to prevent your dust collector from working against you in your war on fine dust. One of the most effective is to locate the dust collector outside or in a room that's separate from your shop and has its own ventilation system. For climates and shop layouts that make this solution impossible, the best alternative is to outfit the dust collector with a filter that traps fine dust particles.
For most dust collectors, a shaker felt filter bag offers a simple, affordable filter upgrade. Shaker felt is a fabric specially designed to trap small dust particles (down to 1 micron) without seriously impeding the air flow of the dust collection system.
Many dust collectors come standard with a filter that does a pretty good job with fine dust. Some are available with a "canister" filter consisting of a pleated fabric filter encased in a metal mesh container that fits on top of the dust collector. Many of these catch dust in the 1- or 2-micron range, and the pleated filter material greatly increases the air filtration surface area. The increased surface area means less airflow resistance and a longer time between filter cleanings.
For shop vacuums, it's best to look for a unit or filter that clearly states the particle size it will capture. Or look for these letters: HEPA. They stand for "high efficiency particulate air" and apply to filters designed to catch 99.97 percent of particles 0.3 microns in diameter.
Shop Air Filtration Systems
Even if you've done everything you can to improve your dust collection system's filtration performance, don't be surprised to find that a coat of fine dust still settles on the surfaces in your shop. The fact is, much of the dust created in a woodshop never enters your dust collection system at all. In spite of your best efforts to set up an efficient, powerful dust collection system, some amount of the fine dust created by the tools it services will always escape into the air in your shop. Dust created by hand-held sanders, for example, is among the finest dust created in the shop and is extremely difficult to completely capture.
Over time, the fine dust problem multiplies. The fine dust particles missed by your dust collection system remain in your shop, ready to be stirred into a dust cloud by the slightest movement of air; you'll add to the problem every time you use your shop.
The answer is air filtration. An air filtration system picks up where your other dust collection efforts leave off by continuously scouring the air in your shop of tiny airborne dust particles. Like dust collectors, the performance of an air filtration system is measured by the volume of air the unit will move in cubic feet per minute (cfm). To be effective, an air filtration device should be rated to cycle through the entire volume of air in your shop 6 to 8 times per hour. The Jet AFS-1100B Air Filtration System, for example, has a maximum setting of 1044 cfm, which means that it will filter entire volume of air in a 20' X 20' shop more than 12 times per hour. Like many air filtration units, it has a built-in timer with settings for 2, 4 and 8 hours, making it a very convenient system to use - just flip the switch when you walk into your shop and forget about it.
Even with dust collection and air filtration in your shop, some woodworking tasks – such as belt sanding or sawing MDF – generate enough fine dust to require the additional protection of a dust mask or respirator. Disposable dust masks are a lower-cost option, but be sure they have two straps and are rated at least for N95 filtration. When using disposable masks, make sure to crimp the nose tab to conform tightly to your face. A tight seal is crucial. If fogging of glasses or goggles is a problem, masks with exhaust valves are available. Washable cloth-style dust masks such as the Dust Bee Gone™ masks also offer excellent protection and reduced fogging, and they're reusable. Again, just be sure you're able to get a tight seal. For serious respiratory protection, powered air-purifying respirators such as the Trend® Airshield enclose the user's face behind a shield and circulate filtered air continuously though the sealed space. These also are a good option for woodworkers whose facial hair make it difficult to get a tight seal with regular masks. (For more, see "Dealing with Fine Woodshop Dust: Personal Respiratory Protection.")