Why Steam Burns Your Twice

The downside to the remarkable invention of the steam engine is the actual steam itself. At the end of a cycle, the steam use to move pistons and drive the cycle must be released as exhaust. This translates into a high-temperature, high-pressure vapor (with a high heat of condensation) effusing at high speeds. If a human limb or digit gets in the way of this potent jet, it means sure destruction of the epidermis, papillary dermis, and even reticular dermis portions of the skin. In layman's terms, you're going to get burned...bad (a second-degree burn). Such steam hazards are ever-present in numerous industrial situations. (The reason you don't have to worry as much of a steam burn when boiling water is discussed later.) In order to understand why simple steam can cause so much damage to the human skin, we must investigate the way that steam burns work. In order to change the phase of water into steam, 538.7 cal/g must be supplied. In other words, 538.7 calories are absorbed by every one gram of water vaporizing into steam. Therefore, as vapor, steam is carrying this vast amount of energy used to change phase. So, when this steam (presumably at 100 Ñ"C) comes in contact with 37 Ñ"C human skin, it condenses and turns to water. In doing so, every gram of steam condensing releases 538.7 calories onto your skin. By now, you already have a major burn, but it is not over. The water (formed by the steam) is still on your skin (and due to the liquid-vapor plateau on the time vs. temperature graph) and it is still at 100 Ñ"C. This is because when changing phases, the substance doesn't change temperature. Therefore, you have boiling water on your skin, which releases one calorie for every one gram of water cooling down by one Ñ"C (specific heat of water). This water has to reach a considerably lower final temperature than 100 Ñ"C, so this goes on for some time. After these two "phases" have occurred, the burning process is over. So, steam burns are so dangerous because they actually burns you twice: the big burn comes when the vapor condenses (releasing energy), and the second follows when the boiling-hot water cools off on your skin. In addition, if you have superheated steam (above 100 Ñ"C), this double-punch becomes a triple-whammy because the vapor has to cool off before it condenses. (In most industrial cases, the steam is superheated because of the immense pressure, which raises the boiling point).