A good fit means the respirator will seal to your skin. A respirator can only work when air passes through the filter. Air will take the path of least resistance, so if the seal isn’t there, the air will go around rather than through the respirator – and therefore lessen the protection.
You’ve put on your respirator and other safety equipment. It’s time to get to work. You know your employer chose appropriate equipment for your job, and you passed your annual respirator fit testing. So you’re good to go, right? Not until you perform one easy task that should be an ingrained habit every time you use a respirator: a user seal check.