Blowdown is a planned or unplanned release of pressurized natural gas from stations, equipment (vessels) or pipelines. In high pressure pipelines, the blowdown leads to low temperatures within the fluid and high vent rates due to larger gas inventory volumes. Blowdown is a hazardous operation, and for this reason several methods have been proposed to improve the accuracy in the estimation of the blowdown rate and the blowdown time in pipelines. In general, these approaches include either physical volume or pipe models with numerical and analytical methods of solution. For instance, a very simple approach for the estimation of the blowdown time is presented by American Gas Association (AGA); this approach can be used a as first-approximation to verify the size of the blowdown stack/valve.