In A Nutshell
We commonly use the word “fume” as a catch-all to describe any airborne contaminant we might breathe into our bodies. Although that is a popularly accepted definition, technically, a fume is a complex mixture of very fine particulate created by the heating of a solid (usually a metal) above its boiling point. So unless you’re a welder, when you say “I was choking on fumes”, you were probably coughing because of some other form of airborne pollutant.
The Whole Bushel
Next time you are filling up the gas tank on your vehicle, look at the warning sign posted near the pump. It should say something like “Extremely flammable—vapors will explode” and “Long-term exposure to vapors has caused cancer in laboratory animals.” Notice they do not refer to “gasoline fumes”; in fact the word “fume” does not appear at all in the warning signs. That’s because gasoline produces vapors, not fumes.
Go to any newspaper or media source and you will likely see the word “fume” used frequently. A headline might scream: “Ten Homeowners Overcome By Toxic Fumes,” or “Hazardous Fumes Force Evacuation of Neighborhood.” The word “fume” has come to mean anything harmful that is exhausted, emitted, or expelled from a source—a smokestack, a furnace, a septic pit, and so on. But even though we call the carbon monoxide gas coming from a kerosene space heater “toxic fumes,” those would be a toxic gas, not a fume.
So what is a fume?
A fume is created when a solid material, usually a metal, is heated and volatilized, and then that volatilized form of the solid condenses in cooler air. If you have ever welded metal (or seen someone welding), that smoke or haze you see coming from the welder is a fume. The welding torch heats the metal above its boiling point which creates a vapor. That vapor quickly condenses when it hits cooler air and creates a complex mixture of very fine particles in the air—a fume.
The cloud of fume created by welding is composed of particulate: metals such as chromium, nickel, iron, and manganese, fluorides, oxides of metals, silicates, and more potentially harmful stuff. Breathing the fume can cause a disease known as “metal fume fever” which, as the name implies, closely mimics flu-like symptoms—fever, muscle aches, chills, headache, nausea, etc. So when a welder claims he was made sick by “toxic fumes,” he is correct, both literally and figuratively.
So while we use the term loosely, there are many things we encounter that are not fumes. Let’s say you get up for work, step on the floor, and kick up dust: These are suspended solid particles in the air. Then you go to the bathroom and spray your underarms with deodorant. That spray you see coming from the can is an aerosol: a mixture of solid and liquid particles in a gas. You walk outside to your car and that morning haze is a mist: a suspension of tiny water droplets in the atmosphere. If a lot of those tiny water droplets get together, they create a fog. Start your car and throw in the exhaust from your vehicle and you help to create smog, which is a mist or fog combined with atmospheric pollutants. Stop at the gas station to fill your tank and those shimmering waves rising from the nozzle into the air are vapors – the gaseous form of the liquid gasoline. The tailpipe of the idling car next to you spits out a mixture of water vapor, and partially combusted particles from burning the fuel, what we call “exhaust emissions.” It’s exhaust all right, but it is not a fume.
While all of those examples do involve some form of airborne pollutant, none of them are actually fumes. Unless you are a welder or work in a factory where metal is fabricated you will probably never in your life be exposed to real fumes.
Show Me The Proof
Toxicology Principles for the Industrial Hygienist, edited by William E. Luttrell, Warren W. Jederberg, Kenneth R. Still
Canadian Centre for Occupational Health and Safety: Welding—Fumes and Gases
Toxic fumes force evacuation of Abington senior housing units