The Atmosphere Detritiation System (ADS) for ITER is being designed to provide the required cleanup of tritium spills into the building and into inert atmospheres for the lowest cost while meeting required emission regulations and limits. Since the CDA phase, changes in the reactor and building design, a new containment philosophy and vacuum vessel maintenance requirements have resulted in adoption of modular designs of the ADS. This paper describes how the different conditions were implemented in hardware and why the number of ADS modules of the present ITER are less than those specified during the CDA phase. The paper will also indicate how volume reduction features of technologies such as membrane humidity-air separators, could be used in ADS if sufficiently developed. The application of low inventory molecular sieves and hydrophobic catalysts will also be considered.