Have you ever noticed that when you take a pot of boiling water off the heat, it stops bubbling but starts steaming profusely?
The answer is technically no, because despite appearances that is not what is happening. Steam or water vapor, that is H2O in a gaseous state, is usually invisible. The visible white smoky substance associated with steam is liquid water suspended in the air, which being more molecularly dense does absorb and reflect enough light to be visible. When water vapor condenses into liquid in the air, rather than on a solid surface, it forms many extremely tiny droplets. These droplets usually begin from a speck of dust or other solid particle suspended the air, which “collects” water in the air is it moves about, a process called nucleation (the solid particle becomes the “nucleus” of the droplet). These tiny droplets, which individually weigh almost nothing, are easily suspended in the air. This is why clouds float high above the ground despite containing many tons of water.
Whenever steam hits cold (read: roughly room temperature or colder) air, some of the vapor loses its kinetic energy to the surrounding gases and cools enough to condense into liquid. As a result, under almost all the circumstances in which humans usually encounter steam, there is also a lot of liquid water suspended in the air making visible white clouds. This association is so ubiquitous that to most people, that white cloudy substance is steam. This even extends to situations where the water is obviously not boiling hot, such as shower “steam”.
While this mass conflation is curious, it may not be apparent why it matters. The key is this last point about “steam” not always being boiling hot. On the contrary, visible clouds are specifically not boiling hot. There are two ways this can be dangerous. First, if people form the association that “steam” can be merely warm, they may underestimate the danger associated with steam, even if they can see clouds of suspended droplets. Second, if people form the association that the liquid droplets are boiling hot steam, they are likely to assume that more steam must mean more visible clouds, which is not necessarily the case. It is the contrapositive of this assumption that makes it dangerous: when there is little to no visible mist at all, such a person is likely to assume there is no steam and thus no danger. However, the amount of visible suspended droplets depends on the temperature, pressure, and humidity of the air, not solely on the amount of water vapor. In an already hot and humid environment, a pipe leaking steam is unlikely to produce a lot of visible mist, for example. This fact can and had caused people to suffer burns.
Steam is dangerous. It’s hot, invisible, and often encountered shooting into the air with great pressure. Steam at 100 °C burns skin more easily than liquid water at 100 °C. Even though liquid water has better heat transfer properties, steam at the same temperature has the extra heat energy associated with the phase transition. This is called the enthalpy of vaporization or latent heat of vaporization. In order for 100 °C steam to lower in temperature (i.e., to reach equilibrium with human skin), it must first shed the energy of vaporization and condense into a liquid.
I don’t think it’s very realistic to try to change language to exclusively refer to suspended droplets as “mist”, “fog”, or “clouds” rather than “steam”, which is otherwise what I would suggest. Instead, I think we have to come to terms that “steam” doesn’t always refer to water vapor and talk about the fact that it has two distinct meanings. Steam is by no means a significant threat to humanity or a problem for humanity, but I don’t like to only consider important problems. There are things we can improve in ways that don’t prevent us from making other improvements, with the possible exception of requiring a small amount of additional thought. These are the small things we do that improve everyone’s lives, including general acts of kindness. One of those things is talking about things in a way that does not lead to potentially dangerous misconceptions. It’s not a big deal by any means, but I still think it’s worthwhile. We ultimately create the culture and society we live in, and we can decide to make it better in small ways every day.
Photo by cottonbro studio
thoughts on mind 