The hot oil process flow illustrates how the fluid is heated by direct contact with the heater element, pumped to the process heat user, and returned to the heating system. This is a continuous process, and many plants operate continuously. As illustrated in the process flow diagram below, Oxidation happens in all organic heat transfer fluids, which react with air to form organic acids. This oxidation rate is lower at ambient conditions but increases rapidly with temperature and doubles every 20°F (11°C) over 200°F (93°C). It should be noted here that hot oil heating is safer than heating processes involving steam for several reasons. Since the system does not require pressurization, the risk of a dangerous explosion is eliminated.