Flares
by Chris Woodford. Last updated: July 23, 2011.
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: 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.
What is a 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: Left: A group of Minnesota Air National Guardsmen ignite MK-13 flares during survival training.
Note that they're wearing gloves to protect against the immense heat the flares give off.
Photo by Erik Gudmundson courtesy of US Air Force.
Right: 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.
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.
Colors
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.
Chemical ingredients
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).
