An employer cannot allow employees who have any condition that interferes with the face-to-facepiece seal or valve function to wear respirators with tight-fitting facepieces. Examples of these conditions include, but are not limited to, missing dentures, the presence of facial scars, the wearing of jewelry, or the use of headgear that projects under the facepiece seal. This provision prohibits employers from placing an employee in a tight-fitting respirator if there is any factor that could prevent an adequate facepiece-to-face seal. Respirator use is permitted where conditions such as missing dentures or facial scars do not prevent an adequate seal.