We get two questions about respirators more often than all other questions combined. People want to know what size mask to order, and they want to know how they can be sure the mask is fitting properly. Because these are such common questions, you'd think we'd have a quick and easy answer for each of them. But each question has some variables, and it's not so easy. Here's what you need to know to make sure your respirator mask fits correctly. For this discussion we will limit the scope to reusable masks like the 3M 7500 Series Half Face Mask or the Moldex 7000 Series Masks. Both of these manufacturers produce different size masks. But because the shape of people's faces vary so widely, there is not a standardized size (4 inches across and 5 inches high, for example). Moldex and 3M both operate under the belief that most faces are about the same size. 80% of people fit the Medium size in these masks. For the 10% on either side of that middle range, with either a larger or smaller face, we generally say those folks will have a good idea about their face size because of previous experience with hats and sunglasses. What we are trying to achieve with a properly fitting respirator mask is the elimination of gaps around the face seal. When you breath in, you want all the air coming through your filters or cartridges. The only real way to know if your mask is fitting properly is to perform a fit test. OSHA requires employers to verify the masks they provide are properly fit. However in practice it's most often only the larger companies that administer fit tests for their employees. In practice, people test them unscientifically by taking the cartridges or filters off and putting the palms of their hands over the air intake holes and breathing in. If you're still able to take in air (so the thinking goes) there are gaps in the seal that will also let bad air in while working. Obviously this isn't as effective as a properly administered fit test. But it's better than no checking at all. If you have the right cartridges, and you are still smelling the odor, fumes, or vapors you are attempting to block, you obviously don't have a properly fitting mask. People generally find they fit one manufacturer better than another because of slight variations in design. If you're not having luck with your 3M mask, consider trying a Moldex mask or something from another manufacturer. If you have questions about your respirator, or your future respirator, remember we are here to help.