The Design Institute for Emergency Relief Systems (DIERS) has developed methodologies for sizing relief devices for two-phase flow. Good engineering practices which account for two-phase flow will ensure against undersized relief devices and potentially catastrophic vessel overpressurization. Application of the DIERS tools and methodologies for two-phase flow can be a formidable undertaking for the uninitiated. This paper attempts to mitigate some of the complexities by a discussion of tempered systems in an integrated form. Tempered, gassy and hybrid systems are identified. Both reactive and non-reactive systems will be considered. The integrated relief system consists of the reactor, relief device, and vent line. The design equations are presented with their underlying assumptions and application limitations. The importance of experimental design data is stressed. The “omega” methodology is discussed with examples.