particularly those in which exothermic reactions are carried out. Such reactions include many classes of industrially important processes including polymerizations, nitrations, diazotizations, sulphonations, epoxidations, aminations, esterifications, neutralizations, and many others. Pressure relief systems can be difficult to design, not least because what is expelled can be gas/vapor, liquid, or a mixture of the two – just as with a can of carbonated drink when it is suddenly opened. For chemical reactions, it requires extensive knowledge of both chemical reaction hazards and fluid flow. DIERS has investigated the two-phase vapor-liquid onset/disengagement dynamics and the hydrodynamics of emergency relief systems with extensive experimental and analysis work. Of particular interest to DIERS were the prediction of two-phase flow venting and the applicability of various sizing methods for two-phase vapor-liquid flashing flow. DIERS became a user's group in 1985. European DIERS Users’ Group (EDUG) is a group of mainly European industrialists, consultants and academics who use the DIERS technology. The EDUG started in the late 1980s and has an annual meeting. A summary of many of key aspects of the DIERS technology has been published in the UK by the HSE. See also Blowoff valve Rupture disc Safety valve Surge control References External links PED 97/23/EC; Pressure Equipment Directive – European Union. Piping Pressure vessels Safety valves ru:Сбросной клапан (сантехника)