A filter designated A2 is intended for protection against a specific group of harmful substances. The letter "A" indicates that the filter captures organic gases and vapours with a boiling point higher than 65 °C. Such substances include, for example, solvents, varnishes, paints, or certain sprays. The digit "2" then specifies the class and capacity of the filter. Class 2 represents a medium filtration capacity, meaning the filter is suitable for working in environments with a medium concentration of these substances and provides a longer protection period than a Class 1 (A1) filter.