Unless other PPE is also used, contamination still results through dermal absorption, even with an approved respirator. For example, organo-phosphate pesticides such as Malathion. With those severe limitations in mind, evaluate each work situation before choosing a respirator. Select a specific respirator designed to function safely within the boundaries you determine. If there is no respirator that fits the limits you select, reevaluate your selection.
Respirators work by using either a chemical or mechanical filtration system.
Chemical cartridges use specially treated activated charcoal or other substances that have a high absorption capacity. Mechanical filter elements provide protection against particulate matter such as dust, mists or metal fumes. Mechanical filters work by physically trapping particulate matter. Unlike chemical filters, mechanical filters become more efficient with use, but make it harder to breathe. Therefore, change them when breathing becomes difficult.