#1205 How does a flare gun work?

How does a flare gun work? They trigger an explosive which shoots the flare high into the sky, where it explodes.

There are several different kinds of flares and flare guns are only one type. Let’s look at the others first. The simplest kind of flares are basic smoke flares. These are flares you can put on the ground or hold in your hand over your head. When they are set off, they release enormous plumes of brightly colored smoke to attract attention. The smoke flare contains four things, somewhat similar to a firework. It has to have a fuel that will burn. The fuel has to burn fairly slowly to keep the smoke coming for as long as the flare is needed. Some handheld smoke flares can keep producing smoke for several minutes. Then they need to have an ignition source to start the fuel burning. The ignition point will be covered by a cap that you need to remove. Once that is off, you hit the exposed end of the flare with it, which produces a spark and starts the fuel burning. Then there will be an oxidizer, which provides a lot more oxygen for the fuel and makes it burn hotter, more brightly, and for longer. Then there is something to color the smoke, such as strontium nitrate or magnesium. The majority of flares are red, although you can get different colors. They are usually red because we associate it with danger and because it is very easy to see red against the blue or the white of the sky. These flares don’t generate much light, but on a clear day, the plume of smoke is visible from a long way away. The advantage of these flares is that any rescuers can very easily track the plume of smoke back to its source.

Then there are rocket flares. These are much more like fireworks and have two parts. They usually come in a tube. To fire them, you take the cap off and bang the other end on the floor, or a hard surface. There is a percussion cap that explodes and lights the first stage of the rocket, which is the part that propels the rocket high into the air. When the rocket is ignited, a timed fuse is also lit. This burns down and ignites the flare part of the rocket when it reaches about 100 m. This part has fuel, often sawdust or magnesium, an oxidizer, often potassium nitrate, and a colorant, usually strontium nitrate. When the fuse ignites this bundle, it explodes with a bright flash, then the red smoke spreads out across the sky as the fuel burns and the oxidizer provides more oxygen. Rocket flares are easier to see from further away because they go higher.

And then there are flare guns, which are basically the same as rocket flares, but they go higher and they are fired from a gun. When the trigger is pulled, the firing pin strikes the percussion cap and the flare is launched out of the wide barrel of the gun. If the gun is pointed straight up, the flare can reach 300 m in height. The flare explodes in the same way as with a rocket flare, except a lot of flares from a gun are fitted with a parachute, which is deployed and allows the flare to float down slowly, prolonging the time it is in the air and visible.

There are also flares that work underwater. It seems like a flare shouldn’t work underwater because they rely on the fire triangle, and water will either remove the oxygen or the heat from the triangle, making the flame go out. Underwater flares get around this by carrying their own oxygen with them. The flare has a fuel, just like the above water flare, but it also has oxidizers and finely ground metals like calcium or magnesium. When the flare is lit, the oxidizer and the powdered metal burn. The metal burns with a very high temperature, too high for the surrounding water to cool it down, and the oxidizer produces all of the oxygen that the burning metal and fuel needs. That means the flare can keep burning despite the water.

Flare guns are often called Very guns because they were popularized by a naval officer called Edward Wilson Very. He is sometimes said to have invented the flare gun, but he was beaten to it by almost twenty years. Martha Coston, an inventor in the US, managed to develop a “pyrotechnic night signal” which were called Coston flares and were widely used during and after the Civil War. The US government used a lot of them and never paid her properly for them. And this is what I learned today.

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