Relief valves are a critical component of a well designed process. Most chemical processes may be subject to pressure and thermal excursions that necessitate an automatic relieving protocol. This relieving is achieved by relief valves at various locations in the process. Each relief valve has to be sized based upon various scenarios that may result in an excursion. It is a systematic process that must also incorporate the results of a Process Hazard Analysis (PHA). In most cases, the relief valves will direct the gases and liquids into a flare system. The hydraulics of the flare system have to be sized to accommodate maximum relieving rates. An example of a relief valve sizing is shown below.