Steam is a better purge material – it is easier to control. I like to see the emergency steam connected to the regular velocity steam line. This helps to keep the emegency steam line clear and free from plugging. The purpose of the emergency steam is to sweep the line free of oil, so some care and thought must be given to the volume actually required. Too much too-fast can cause a drum foam over, if the emergency purge happens when the drum is almost full. Make sure the pressure of the purge/velocity steam is high enough to avoaid oil flowing backwards through the steam line. The blocked in pressure of the furnace charge pumps will help drive the decision of steam vs water.