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A flare gun being fired from a ship.

Flares

by Chris Woodford. Last updated: August 12, 2014.

You're out in a boat with a very experienced sailor friend when he starts feeling ill, then collapses on the deck and passes out. You don't know enough to pilot the boat yourself or even how to operate the radio, but there are some flares onboard and instructions showing you how to fire them. You can see there are other boats far off in the distance so you figure it's worth a try. You fire off a flare and it shoots skyward, blazing red high above you. Then you fire off a second one to be sure. Within minutes, the boats are coming toward you and you breathe a sigh of relief; you know help is on its way.

Thank heavens for flares, which have saved countless lives at sea. They're fantastically simple signaling devices similar to fireworks, but they're designed to communicate a much more direct message in an emergency. Have you ever wondered what they're made of and how they work? Let's take a closer look!

Photo: Flare guns like this are used to fire distress signals and warnings at sea. Photo by Joshua Wayne LeGrand courtesy of US Navy.

What is a flare?

Top: A group of orange smoke flares being set off. Bottom: Closeup of an orange smoke flare.

A flare is a tube packed with explosive chemicals that burn very brightly or give off smoke, usually to attract attention in an emergency. The two main kinds are handheld flares (which operate on the ground) and rocket flares (which are fired into the air).

Handheld flares

Handheld flares also come in two kinds. Signal flares burn with a bright red light as you hold them, while smoke flares (also called smoke signals) are designed to be held in the hand, placed on the ground, or dropped overboard into the sea to give off huge plumes of colorful (generally orange or red) smoke. Flares like this are typically visible up to about 5km (3 miles) away for anything from 30 seconds to several minutes. Since smoke doesn't generate light, smoke flares are useful only in daylight.

Photo: Right: Handheld smoke flakes: Top photo: A group of Minnesota Air National Guardsmen ignite MK-13 flares during survival training. Note that they're wearing gloves to protect against the heat the flares give off. Photo by Erik Gudmundson courtesy of US Air Force. Bottom photo: Here, a smoke flare canister is being used to signal troop positions to a helicopter during a search-and-rescue survival exercise. You can just see the flare on the bottom left (it's the white tube with orange ends). Photo by Brandt Smith courtesy of US Air Force and US Navy.

Rocket flares

Rocket flares are bright enough to work in daytime or night. They're usually fired high in the air so they can be seen from much greater distances than handheld flares (up to 40km/25 miles or so in good visibility). The simplest ones are like fireworks, with two "stages" (separate explosive burning sections) and are entirely self-contained. You hit them on the base (or bang them on the ground or the deck of a ship) to strike an explosive percussion cap. This triggers the first stage, which propels the inner part of the flare into the air for several seconds. At that point, when the rocket has reached a height of maybe 100m (300ft) or so, the second stage ignites and the flare explodes with an intensely bright red or orange light. Some flares release red stars.

Another kind of rocket flare is fired from a specially designed flare gun or Very pistol (named for American naval officer Edward Very, who invented it in 1877). These flares are aluminum tubes about 3cm (just over an inch) in diameter and 30cm (12inches) or so long. When they're fired, they shoot rapidly to a height of about 300m (1000ft). At that point, they explode with a loud bang and release a brightly burning flare suspended from a small parachute that drifts very slowly downward, maximizing the amount of time for which it can be seen.

Closeup of a flare showing the aluminum tube that contains it. Firing a flare gun from a ship.
Photo: Left: Rocket flares are packaged in aluminum canisters like this. Right: Firing a flare from the deck of a ship. Both photos by Joshua Wayne LeGrand courtesy of US Navy. Original photos are here and here.

How a flare gun works

Labeled cutaway diagram of flare gun designed by John Smith in 1942, US Patent 2,356,709.

I don't have a picture of Edward Very's original flare gun, but here's a more recent design. This World War II model was invented in 1942 by John R. Smith for the Harrington & Richardson company and patented in 1944. As you can see, it looks much like an ordinary handgun and the basic operation is very similar:

  1. Trigger: As in a conventional gun, you simply pull your finger back to release the hammer.
  2. Hammer: Pivots around a central pin. It's called a hammer because that's how it works: like a conventional hammer driving a nail into wood, it uses a relatively large mass pushing forward onto a relatively small mass (the firing pin), so it magnifies force.
  3. Firing pin: Strikes the back of the flare and causes it to explode and shoot off down the barrel.
  4. Barrel: Flare guns don't need to fire the same way as conventional firearms (they fire bigger projectiles, don't need to send them so far, and don't need to fire as accurately), and they often have a smooth barrel instead of the rifled (grooved) barrel that you'd find on a conventional gun (which spins bullets and makes them fire more accurately). Flare gun barrels are also wider than those in a conventional gun; in other words, the caliber (internal diameter of the barrel) is greater. A typical flare gun caliber is 26–30mm (1–2 inches), which is about 5 times wider than a .22 rifle (~5.5–5.7mm).
  5. Shell extractor mechanism: The barrel can be pivoted for loading/unloading.
  6. Main spring: Stores energy to power the hammer toward the firing pin.

Artwork: From US Patent #2,356,709: Flare Gun by John R. Smith, courtesy of US Patent and Trademark Office.

What colors are flares... and why?

Red and orange flares always indicate distress and if you see one you need to take action. White flares work in the same way but are usually designed to illuminate an area at night (for example, if someone falls overboard) or to prevent imminent collisions at sea (by indicating a ship or boat's position to another vessel); they don't normally indicate danger.

What makes a flare fire red or orange? Just like a firework, it's the chemicals inside, which are chosen specifically so the flare burns brightly and with a specific color. The main ingredients of flares include strontium nitrate (which provides the color—it burns with a bright red or orange-red flame), potassium perchlorate (a powerful oxidizer, which makes the strontium burn rapidly), and magnesium (which burns very brightly). Unfortunately, perchlorates (containing chlorine) aren't very environmentally friendly, so organizations like the US Navy have been working hard to develop perchlorate-free flares using copper (to make a green color) and polyvinyl chloride (to enhance the color).

Warning!

Aeromedical students set off rescue flares as night falls.

Flares are a good thing to have with you, but remember that they're to be used only in emergencies. They're designed to get you out of danger but, ironically, they are themselves very dangerous: they contain explosive chemicals and, let off the wrong way, they can cause serious injuries and fires. Flare guns are regarded as firearms in some states or countries and their use may be banned or restricted by law. If you plan to carry flares, be sure to familiarize yourself with exactly how they work before you need to use them. Read the labels carefully, follow any safety guidance to the letter, and don't store them longer than it says on the packet. Be sure to find out any rules, laws, or signaling conventions for using flares in your particular country or region.

Photo: Above, left: Air Force medics practice setting off rescue flares as part of their survival training. Photo by Efrain Gonzalez courtesy of US Air Force.

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Text copyright © Chris Woodford 2010, 2014. All rights reserved. Full copyright notice and terms of use.

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Woodford, Chris. (2010) Flares. Retrieved from http://www.explainthatstuff.com/flares.html. [Accessed (Insert date here)]

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