我同意下面这个解释。
http://answers.yahoo.com/question/index?qid=20080630104754AAZU39FThere are several misconceptions that are in evidence in some of these responses. The first is that steam is hotter than boiling water.
It can be, but the steam produced from boiling water will be the SAME temperature as boiling water, 100C. To compare steam and water we need to keep all the variables constant except one, the phase.
We would need to compare 100 grams of steam at 100C to 100 grams of water at 100C, and both would have to come into contact with the same patch of skin for the same length of time.
And if all of that occurred, then the steam would impart more heat to the victim. The steam would first lose the latent heat of vaporization to condense into liquid water at 100C which would then be equivalent to the water at 100C.
The boiling water or the 100C water from the condensed steam would then give up the same amount of heat as the temperature droped to some constant final temperature.
The difference then, is the latent heat of vaporization, which is quite large for water. That additional heat would do a great deal of damage to the person unfortunate enough to come into contact with the steam.
Also, while on the subject of steam, some folks think they can see steam. Water vapor is invisible. What some folks call steam is actually a small cloud formed as steam condenses to tiny droplets of liquid water. If you can see it, it's not steam, it's liquid water.