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The Myth of Lamp Oil

In 2003, at the request of the publisher of one of our toy train hobby magazines, I wrote the following essay about the use of lamp oil as smoke fluid in our toy train locomotives.  It appeared in an issue of the magazine that year.  Unfortunately, everything old is new again and the topic keeps resurfacing in various online venues as people "discover" lamp oil.  Its use as a smoke fluid remains as dangerous as ever and I thought that I'd give the essay a permanent home by publishing it here on my web site, where a Google search will turn it up so that people can read the facts about just how dangerous it is to use something other than the appropriate smoke fluid in a locomotive.  The essay has been slightly updated from its original form as published six years ago.

To start with, "lamp oil" appears in quotes because it's a term that is used to describe a wide range of products. "Lamp oil" is simply a petroleum-based liquid that can be burned at a wick in a lamp; if you think of an old kerosene railroad lantern, you have the general idea. In times past, "lamp oil" also included other types of liquids, such as those derived from coal and those derived from whales (yes, whale oil). Today, the "lamp oil" that is commercially available falls into three broad classes of petroleum-based materials: light petroleum distillates, kerosene, and mineral oil. These are three very different materials with very different physical properties. What they have in common is that they will all burn at a wick in a lamp and hence can be sold as "lamp oil."

Without getting overly technical, the flammability of a given liquid is rated based on its flash point. This is the temperature at which it will give off enough vapor to be ignited (start burning) at the surface of the liquid. The lower the flash point, the more flammable the material is. Under the categories established by OSHA, any liquid that has a flash point below 100 F is considered flammable (i.e., it will ignite at normal working temperatures). A flash point between 100 F and 200 F means that the liquid is considered to be combustible (i.e., it will ignite at elevated temperatures).

Let's talk about our trains for a minute. Mineral oil is the primary constituent of most toy train smoke fluids (but not all, LGB/Seuthe being the notable exception) based on the material safety data sheet (MSDS) that you can obtain from the manufacturer. Mineral oil comes in a variety of weights or viscosities, each representing a slightly different fraction of the petroleum from which it is derived. The heavier the mineral oil, the higher the viscosity, the higher the boiling point, and the higher the flash point. Toy train smoke fluids are a medium viscosity mineral oil; using MTH smoke fluid as an example, the flash point is about 265 F, meaning that it is neither flammable nor combustible.

Getting back to "lamp oil", if you're lucky enough to get a bottle that contains mineral oil (and many "lamp oil" bottles do not tell you what kind of fuel is contained therein), yes, it may work in your smoke unit. Chances are it's a lighter weight mineral oil (thus more easily ignited and burned), which means it will boil off faster and you'll have to refill your smoke unit more often lest it run dry and the wicking burn, ruining your smoke production (this same problem holds true for some third-party smoke fluids). But what if it's not mineral oil at all, as the available online data sheets for "lamp oil" indicate is a real possibility?

As I said above, there are two other materials that are sold as "lamp oil": kerosene and light petroleum distillates. If you get a bottle filled with the light petroleum distillates, you've got a material with a flash point of about 170 F, which means it's combustible. If you get a bottle filled with kerosene, the flash point is about 95 F, meaning that it's a flammable liquid. It's not as bad as lighter fluid (flash point about 50 F), but it's nothing to play with either.

Our toy train smoke units (again with the exception of Seuthe) work by heating up one or more elements that are in contact with wicking that's saturated with smoke fluid. The smoke fluid boils and as the vapor condenses when it leaves the smokestack, it forms a fog which we see as the "smoke." In order to boil the smoke fluid, the heating elements get really hot!

So what's the bottom line? Yes, you can buy lamp oil and substitute it for smoke fluid. If it's based on mineral oil, it may work. If it's based on light petroleum distillates or kerosene, it may well ignite and shoot flame out of your stack; think about that as your train circles the Christmas tree with the low-hanging branches! And, if it is kerosene and you're boiling it to create a cloud of kerosene vapor, flame may be the least of your worries; it's quite possible that it will blow up in your face! And remember, chances are that just looking at the "lamp oil" bottle you aren't going to be able to tell what kind of fluid is inside.

In the strongest possible terms, as a chemist and as someone very involved in the safety program where I worked, I recommend that you use the smoke fluid in your locomotive that is recommended by your manufacturer! Does it cost a few cents more? Yes. Is it worth setting a fire or possibly injuring yourself or others to save those few cents by using "lamp oil"? Absolutely, categorically not!!

Two final notes. First, a word about Seuthe smoke units. They work very differently than the conventional smoke units described above and require a very different smoke fluid, a much lighter (and hence more flammable) material with a substantially lower boiling point. You should always use LGB/Seuthe smoke fluids in a Seuthe smoke unit; using mineral oil-based smoke fluids can plug up the Seuthe unit. On the other hand, you should never use LGB/Seuthe smoke fluids in a conventional toy train smoke unit; it will boil off very quickly, resulting in burned wicking, and can possible ignite.

Last, you may see mention of "paraffin" on bottles of "lamp oil." They're not talking about the wax used in candles and home canning. In this case, in the United States, paraffin means mineral oil. Which might be well and good except that, in the rest of the world, paraffin means, are you ready for this, kerosene! So a label of "paraffin" on your bottle is not at all a good indication of what's inside.  I have a bottle of "lamp oil" that says that its "100% pure paraffin" and whose front label also bears the American flag.  In small print, the back label says that the contents are imported from Hong Kong.  Testing showed the material in the bottle to be kerosene!  It burns really well in a hurricane lamp.  But in the smoke unit of a locomotive?  No thanks!

Last updated: 22 Jan 2020

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