At the same temperature, steam burns are often more severe that water burns because of water's high HEAT OF VAPORIZATION. Water possesses high heat of vaporization. The heat of vaporization refers to the amount of heat that is needed to convert a unit mass of water to gas. After getting to the boiling point, a lot of heat is still needed to be absorbed by a boiling water before it can be converted to the gaseous form. Thus, the heat that is inherent in the steam is greater than that which is found in the boiling water, that is why the steam causes more damages.
Hydrochloric acid is polar which means it has stronger bonds between it's molecules, unlike diatomic fluorine that is non-polar and has weaker bonds. That's why it has a higher boiling point.
