This Guide uses Critical Quality Attributes (CQAs) and Critical Process Parameters (CPPs) according to the definition given below (from ICH Q8) (Reference 2, Appendix 8), which states that “CQAs are generally associated with the drug substance, excipients, intermediates (in process materials) and drug product.” In this Guide we have applied them to the system output (gas) considering it as an excipient; therefore having direct product contact or becoming part of the final product formulation. This has been done to help facilitate the risk assessment process.