First of all, a dust mask is has a single strap that goes over the head and provides very little protection from particles and debris in the air. They're also called nuisance dust masks and they're best used for mild applications like leaf blowing and general household dust protection. Dust masks just don't provide a good face seal and they protect about as well as nose hair, which is to say not that well. Replace them when they look dirty or after about 8 hours of wear. Honestly they're not doing much anyway, so it won't matter. What we sell for actual lung protection are disposable respirators. I know it sounds like we're a little prickly about this topic. We just want people to be protected. Disposable respirators, unlike a basic dust mask, can do a very good job of keeping harmful particulate matter out of the lungs if they are worn properly and not past their useful life. A good rule of thumb for replacing your disposable respirators is to change them out when they are soiled, damaged, or if breathing becomes difficult. The smart people over at Moldex have made some progress in finding ways to keep masks from getting dirty. One thing that happens all the time on a job site is the masks get dirty as soon as you set them down. Moldex makes disposable respirators with an exterior lightweight plastic mesh that helps to keep the actual filter material from contact with dirty surfaces. These masks come in the Moldex 2200 model which doesn't have a breathing valve, or the Moldex 2300 model which does have the exhalation valve. The valve helps to keep the wearer a bit cooler over long periods of working in the mask. Breathing in a disposable respirator can become difficult if the filter material becomes clogged. That's another main reason to change them out. Again Moldex figured out a good solution to this problem by simply creating more surface area. The Moldex AirWave has an accordion surface that both keeps it from getting too dirty, and provides more actual filter material covering the face so it takes more for it to become clogged. Damaged dust masks or disposable respirators need to be replaced. They have a job to do, and if they have a big hole in them, it's going to let in the things you are trying to keep out. What happens more often is one of the straps breaks. Sometimes you can fix them. Most often you can't. One other thing to think about is germs. Don't share dust masks. Most people don't like to do that anyway. But even if your disposable respirator (or dust mask, if you're still using one after this article) seems good after more than a day, change it out anyway. Many disposable respirators have anti-microbial surfaces, but over time they can start to be a home to germs. Change them out after 8-10 hours even if they're not dirty. If you have more questions about lung protection or respirators, we can talk about this stuff all day. Please don't hesitate to give us a call at 1-800-829-9580 or contact us online at www.pksafety.com.