You've installed a dust collection system that takes care of large dust particles and shavings, and you've augmented that with an air-filtration system to continually purify the air in your shop. Do you still need personal respiratory protection? Many experts say yes.
One reason is that the level of safe exposure to woodworking dust is quite low. The National Institute for Occupational Safety and Health (NIOSH) recommends that the average amount of fine dust in wood shop air be no more than 1mg/cubic meter over a 10-hour shop session. For a garage-sized shop, 1 mg/cubic meter amounts to less than 1/8 teaspoon of dust for the entire volume of air in the shop!
Another reason is that many common woodworking operations such as sanding, cutting with a chop saw or using a router can overwhelm all of your dust collection measures and leave you breathing dangerous levels of fine wood dust.
Disposable dust masks are among the most economical and convenient forms of personal respiratory protection. They're best suited for short-term exposure to fine dust and less effective and comfortable in long sessions in a dusty shop. This is because they're made to fit the contours of an "average" face and, in general, don't provide as tight an air seal between your face and the mask, which is what prevents fine dust particles from getting around the mask's filter material and passing directly into the lungs.
Not all dust masks are created alike. It's important to use a mask that is designed to actually filter fine dust, such as the MXV Dust Mask. It features a three layer design that pre-filters course particles, traps fine particles in the interior filter and provides comfortable inner surface designed designed to prevent fatigue over longer periods of use.
Washable Cloth Masks
Reusable cloth masks such as the Dust Bee Gone™ are a little more expensive than disposable masks, but they offer features that many woodworkers think are worth the extra initial expense. Most important, they're reusable – a quick hand washing and they're back to their original filtering performance and comfort. You won't suddenly discover that you've run out of cloth masks, as often happens with the disposable variety. Additionally, cloth masks are more pliable than disposable masks and tend to fit more comfortably for longer periods than many disposable masks. They work great for projects that generate a small to moderate amount of dust, such as wood turning or carving, and they tend to produce less fogging of glasses or goggles.
Power Air Respirators
Power respirators use a battery-powered fan to supply a continuous stream of filtered air to the interior of the mask. They're more of an investment than either disposable masks or reusable cloth masks, but they are also generally considered a giant step forward in comfort. The fresh stream of air helps keep the user cool during strenuous work, and because the mask relies on positive air pressure inside the mask rather than a tight seal to keep the interior of the mask free of contaminated air, the power respirator can be designed to provide a fairly loose, comfortable fit.
Power respirators range in price and performance from less expensive models that resemble a standard respirator mask to more advanced systems that include other features such as a face shield and ear protection. Power respirators are the ultimate in personal respiratory protection and are the best choice for situations where a high level of protection and comfort are desirable. If your work often has you spending long periods in front of a stationary disc or belt sander, for example, an investment in this level of personal respiratory protection is not something you are likely to regret.
For Disposable and Washable Masks, Fit is Key
Whether you choose a disposable dust mask or a reusable cloth mask, ensuring a good seal to your face is crucial. With these types of masks, any gap will allow the smallest and most dangerous particles to enter your lungs. So be sure that your mask has two straps, that the bridge at the nose can be bent to conform to the shape of your face and that the mask seals tightly all the way around. If you have facial hair that makes achieving a tight seal problematic, a power air respirator is likely to be the most effective option.