The SR 231 CL/HC/SD/FM chemical cartridge is used with Sundström half masks and full face masks Air PurifyingRespirators (APR) to provide protection against the following types of gases and vapours:CL protects against Chlorine.HC protects against Hydrogen chloride.SD protects against Sulfur dioxide.FM protects against Formaldehyde.This chemical cartridge is approved for independant use or can be combined with the Sundström particulate filterSR 510, P100 in order to obtain protection against aerosols (particles), e.g during spray painting.