A flare works by burning a compressed pellet of metallic fuel and chemical oxidizer at extremely high temperatures, producing an intense colored flame visible for miles. The core reaction is simple: a fuel (usually magnesium) combines with an oxidizer (like strontium nitrate or potassium perchlorate) to generate heat and light without needing oxygen from the air. That self-contained chemistry is what lets flares burn in wind, rain, and even underwater in some designs.
What’s Inside a Flare
The business end of a flare is a tightly packed pyrotechnic composition. Common ingredients include strontium nitrate, potassium perchlorate, strontium peroxide, magnesium, and black powder (a mixture of sulfur, charcoal, and potassium nitrate). Each ingredient plays a specific role. The oxidizer, typically strontium nitrate or potassium perchlorate, releases oxygen when heated so the reaction sustains itself. The fuel, usually powdered magnesium, burns hot and bright. A binder holds the pellet together and controls burn rate so it doesn’t go up all at once.
Black powder often serves as the ignition charge, the small initial explosion that kicks the main composition into burning. It ignites at a lower temperature than the main pellet, acting as a bridge between the striker mechanism and the high-temperature core.
How Color Is Produced
The color of a flare comes from the specific metal compounds in the mix. Strontium compounds produce red, which is why most emergency signal flares burn red. Barium nitrate produces green. White or silver light typically comes from burning magnesium or aluminum alone, without a coloring agent. The metal atoms absorb energy from the heat of the reaction and release it as light at characteristic wavelengths, each element emitting its own signature color. This is the same principle behind fireworks, just in a more controlled, sustained format.
Igniting the Flare
Most handheld flares use either a friction striker or a percussion cap to ignite. A friction-style flare works like striking a match: you pull a rough surface across a chemically sensitive tip, generating enough heat through friction to ignite a primer compound. Percussion-style flares use a sharp impact, like pulling a string that drives a pin into a small charge, to create a spark. In both cases, the primer ignites the black powder charge, which then lights the main pyrotechnic pellet.
Once the main composition catches, the reaction is self-sustaining. The oxidizer releases oxygen internally, so external conditions like wind or moisture can’t easily snuff it out. This is a key difference from an ordinary fire, which depends on atmospheric oxygen and can be smothered.
How Bright Flares Actually Are
Flare brightness is measured in candela, and the numbers vary dramatically depending on the type. U.S. Coast Guard-approved handheld flares produce 500 to 700 candela of red light and burn for about two minutes. International SOLAS-standard handheld flares are far more intense, rated at 15,000 candela, though they burn for a shorter 60 seconds. The theory is that their much greater brightness compensates for the shorter burn time.
Aerial parachute flares are the most visible type. A USCG-rated aerial flare produces about 20,000 candela and reaches around 400 feet. SOLAS parachute flares hit 30,000 candela and climb to roughly 1,000 feet before deploying a small parachute that keeps them suspended while burning for about 45 seconds. That altitude is what gives them the longest visibility range of any flare type, since the higher the light source, the farther it can be seen over the curvature of the earth and wave crests.
How Aerial Flares Stay Aloft
An aerial flare is essentially a small rocket with a parachute. When fired, a propellant charge launches the flare body upward. At or near peak altitude, a timed charge ejects the burning pyrotechnic element and deploys a small drogue parachute. The parachute slows the descent enough to keep the flare visible in the sky for 30 to 45 seconds rather than falling back to the surface in a few seconds. The burn happens during the slow descent, maximizing the window during which rescuers or nearby vessels can spot the light.
Visibility Distance
At night, a standard 500-candela handheld flare is visible from a few nautical miles under good conditions. A 15,000-candela SOLAS handheld flare extends that range significantly. Aerial parachute flares, with their combination of high intensity and altitude, offer the greatest range. In daylight, visibility drops sharply for all types because the flame has to compete with ambient sunlight. This is why orange smoke signals are often carried alongside pyrotechnic flares for daytime use.
Shelf Life and Disposal
Pyrotechnic flares have a shelf life of 36 to 42 months from the date of manufacture, stamped on the casing. After that window, they become increasingly unstable. The chemical compounds can degrade, making them either unreliable (they might not ignite when you need them) or unpredictable (they might ignite when you don’t). Expired flares cannot legally be used as required safety equipment on boats, and they cannot be discharged outside of an actual emergency.
Disposal is more complicated than you might expect. The EPA classifies expired pyrotechnic flares as explosive hazardous waste, and the Department of Transportation regulates their transport as Class 1.4 explosives. You can’t toss them in household trash or burn them in your backyard. In many states, household hazardous waste collection events or facilities will accept them, though policies vary. Some states, including Illinois, Ohio, and Pennsylvania, don’t accept flares at standard hazardous waste collections at all, requiring you to contact a licensed commercial disposal facility instead. In every case, calling ahead is the recommended step since each location sets its own rules on what it will take.
Because most flares expire unused, the disposal problem is widespread. The Coast Guard now allows electronic visual distress signals as alternatives to pyrotechnic flares on recreational vessels, which sidesteps the expiration and disposal cycle entirely.