Activated carbon filter respirators protect from gas, vapours, fumes, mists as they are filled with special activated carbons that retain airborne pollutants.
The EN 141 standard gives the minimum requirement, the test methods and the markings for gas filters. In the a.m. standard, gas filters are divided into types, A,B,E,K, according to the group of substances they are designed to protect from, and classified as 1,2,3, according to their gas absorption capacity. To every type of filter corresponds the most suitable activated carbon.
Besides the a.m. main classes, there also are multi-purpose filters, i.e. those that combine the protection of more classes together (e.g. AB, BK, ABEK).
It is impossible to state beforehand the actual duration of the activated carbon within a gas filter as it depends, besides the gas concentration, also on many unpredictable factors such as temperature and air humidity and the breathing rate.