Steam burns are more serious than hot water burns even when the water and the steam are the same temperature, according to UCSB ScienceLine. This is because the steam expends energy transferring out of the gas phase into the water phase when it hits the skin. On the other hand, water immediately starts cooling to the temperature of the skin on contact for a less severe burn.
Steam at 100 degrees Celsius contains more energy than water at 100 degrees Celsius, states the University of British Columbia Department of Physics and Astronomy. Although water starts converting to the gas state at 100 degrees Celsius, it takes additional energy for it to make that phase change. The steam carries this potential energy and needs to release it to move back into a liquid state.
When the steam hits human skin, it rapidly cools enough to change back into a liquid phase, maintains the University of British Columbia Department of Physics and Astronomy. During the change, the latent heat of vaporization adds to the actual heat of the steam for a worse burn than with water alone. Pressurized steam is especially dangerous. Pressurization concentrates the heat and energy and delivers it to a proportionally smaller area of skin. Industrial burns from pressurized steam pipes are particularly severe.