A respiration system is provided with a container (1) in which, by an exothermic chemical reaction of a reaction material, CO2 is removed from the respiration air or oxygen is generated, and with an indicator of the consumption of the reaction material. The consumption indicator has a predetermined amount (7) of material which can be melted by the reaction heat of the exothermic chemical reaction. The material is kept in thermal contact with the container interior in such a manner that a measurement of the total reaction heat, and thus the consumption of reactive material, can be read from the degree of melting of the meltable material.