A flare, also sometimes called a fusée, fusee, or bengala in some Latin-speaking countries, is a type of
pyrotechnic that produces a bright light or intense heat without an
explosion
An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known ...
. Flares are used for distress signaling, illumination, or defensive
countermeasures in civilian and military applications. Flares may be ground pyrotechnics, projectile pyrotechnics, or parachute-suspended to provide maximum illumination time over a large area. Projectile pyrotechnics may be dropped from aircraft, fired from rocket or
artillery, or deployed by
flare guns or handheld percussive tubes.
History
The earliest recorded use of gunpowder for signaling purposes was the 'signal bomb' used by the Chinese
Song Dynasty (960–1279) as the Mongol-led
Yuan Dynasty (1271–1368) besieged
Yangzhou in 1276.
These soft-shelled bombs, timed to explode in midair, were used to send messages to a detachment of troops far in the distance. Another mention of the signal bomb appears in a text dating from 1293 requesting their collection from those still stored in
Zhejiang.
A signal gun appears in Korea by 1600. The ''Wu I Thu Phu Thung Chih'' or ''Illustrated Military Encyclopedia'', written in 1791, depicts a signal gun in an illustration.
Civilian use
In the civilian world, flares are commonly used as signals, and may be ignited on the ground, fired as an aerial signal from a
pistol
A pistol is a handgun, more specifically one with the chamber integral to its gun barrel, though in common usage the two terms are often used interchangeably. The English word was introduced in , when early handguns were produced in Europe, an ...
-like
flare gun, or launched from a self-contained tube. Flares are commonly found in marine
survival kits.
Maritime distress signal
Red flares, either sent as a rocket or held in the hand, are widely recognized as a maritime distress signal.
The
International Convention for the Safety of Life at Sea
The International Convention for the Safety of Life at Sea (SOLAS) is an international maritime treaty that sets minimum safety standards in the construction, equipment and operation of merchant ships. The International Maritime Organization ...
(SOLAS) has standards for visual signals, including both handheld and aerial flares. Handheld flares must burn for at least one minute at an average
luminosity
Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...
of 15,000
candelas, while aerial flares must burn for at least 40 seconds with a 30,000-candela average luminosity. Both should burn in a bright red color. Nations that are members of SOLAS require vessels to carry visual signals on board.
Fusee
Another type of flare is the ''fusee'', which burns for 5–60 minutes with a bright red light. Fusees are commonly used to indicate obstacles or advise caution on roadways at night; in this usage they are also called ''highway flares'', ''road flares'', or ''ground flares''. They are commonly found in roadside emergency kits.
Fusees are also known as ''railroad flares'' and are commonly used to perform hand signals in
rail transport applications. Since they can be used only once, fusees nowadays are usually intended for emergency use (as opposed to the lanterns typically used during normal operating conditions). However, in the days before train radio communications, fusees were used to keep trains apart in
dark territory. A railroad fusee was timed to burn for 10 minutes, and quantities were dropped behind a train to ensure a safe spacing. If a following train encountered a burning fusee, it was not to pass until the fusee burned out. Fusees made specifically for railroad use can be distinguished from highway fusees by a sharp steel spike at one end, used to embed the fusee upright in a wooden
railroad tie.
In forestry and firefighting, fusees are sometimes used in
wildfire suppression and in the ignition of
controlled burn
A controlled or prescribed burn, also known as hazard reduction burning, backfire, swailing, or a burn-off, is a fire set intentionally for purposes of forest management, farming, prairie restoration or greenhouse gas abatement. A control ...
s. They ignite at and burn as hot as . They are especially effective in igniting burnouts or backburns in very dry conditions, but not so effective when fuel conditions are moist. Since controlled burns are often done during relatively high humidity levels (on the grounds that they could not be safely contained during periods of very low humidity), the
driptorch is more effective and more often used. Fusees are also commonly carried by
wildland firefighter
A firefighter is a first responder and rescuer extensively trained in firefighting, primarily to extinguish hazardous fires that threaten life, property, and the environment as well as to rescue people and in some cases or jurisdictions also ...
s for emergency use, to ignite an
escape fire in surrounding fuels in case of being overrun by a fire if no other escape routes are available.
Calcium phosphide is often used in naval flares, as in contact with water it liberates
phosphine which self ignites in contact with air; it is often used together with
calcium carbide which releases
acetylene
Acetylene (systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
.
Law enforcement also may use flares (either propped on a biped or laid flat) to signal traffic hazards or that a road is blocked, often as a more visible replacement for traffic cones.
Law enforcement in the United States usually use
magnesium-based flares that last from 15–30 minutes.
Military use
Maritime signal flare
In 1859,
Martha Coston
Martha Jane Coston (December 12, 1826 – July 9, 1904) was an American inventor and businesswoman who invented the Coston Flare (pyrotechnic), flare, a device for signaling at sea, and the owner of the Coston Manufacturing Company.
Early life
Sh ...
patented the Coston flare based on early work by her deceased husband Benjamin Franklin Coston. It was used extensively by the
US Navy during the Civil War and by the
United States Life-Saving Service (the precursor to the
US Coast Guard) to signal to other ships and to shore.
Illumination
In 1922, a "landing flare" was an aerial candle attached to a parachute and used for landing an airplane in the dark. The flare burned for less than four minutes and the
candlepower was about 40,000
lumens
The lumen (symbol: lm) is the unit of luminous flux, a measure of the total quantity of visible light emitted by a source per unit of time, in the International System of Units (SI). Luminous flux differs from power ( radiant flux) in that radia ...
.
Countermeasure
A special variety of flares is used in military aircraft as a defensive
countermeasure against
heat-seeking missiles. These flares are usually discharged individually or in salvos by the pilot or automatically by tail-warning devices, and are accompanied by vigorous evasive maneuvering. Since they are intended to deceive infrared missiles, these flares burn at temperatures of thousands of degrees,
incandescing in the visible spectrum as well.
Tripflares
Flares connected to
tripwires are used to guard an area against infiltration. The flare begins burning when the tripwire is triggered, providing both alarm and illumination.
Regulation
Under the
UN hazard number system, pyrotechnic flares are designated class 1.4 explosives.
Several U.S. states, including California and Massachusetts, have begun regulating levels of potassium perchlorate, which can be unsafe at certain levels in drinking water. Contaminated drinking water can lead to such symptoms as gastric irritation, nausea, vomiting, fever, skin rashes, and even fatal
aplastic anemia
Aplastic anemia is a cancer in which the body fails to make blood cells in sufficient numbers. Blood cells are produced in the bone marrow by stem cells that reside there. Aplastic anemia causes a deficiency of all blood cell types: red blood ...
(a reduction in all types of blood cells).
Chemistry
Flares produce their light through the
combustion of a
pyrotechnic composition. The ingredients are varied, but often based on
strontium nitrate,
potassium nitrate, or
potassium perchlorate
Potassium perchlorate is the inorganic salt with the chemical formula K Cl O4. Like other perchlorates, this salt is a strong oxidizer although it usually reacts very slowly with organic substances. This, usually obtained as a colorless, crysta ...
and mixed with a fuel such as
charcoal
Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, cal ...
,
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
,
sawdust,
aluminium,
magnesium, or a suitable
polymeric
resin. Flares may be colored by the inclusion of
pyrotechnic colorants.
Calcium flares are used underwater to illuminate submerged objects.
Perchlorate flare health issues
Many in-service colored signal flares and spectrally balanced
decoy flares contain
perchlorate oxidizers. Perchlorate, a type of
salt in its solid form, dissolves and moves rapidly in groundwater and surface water. Even in low concentrations in drinking water supplies, perchlorate is known to inhibit the uptake of
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
by the
thyroid gland
The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobe (anatomy), lobes. The lower two thirds of the lobes are connected by a thin band of Connective tissue, tissue cal ...
. While there are currently no US federal
drinking water standard
Drinking water quality standards describes the quality parameter#Environmental science, parameters set for drinking water. Despite the truth that every human on this planet needs drinking water to survive and that water may contain many water poll ...
s for perchlorate, some states have established public health goals or action levels, and some are in the process of establishing state maximum contaminant levels. For example, the
US Environmental Protection Agency has studied the impacts of perchlorate on the environment as well as drinking water. California has also issued guidance regarding perchlorate use.
US courts have taken action regarding the use of perchlorate in manufacturing pyrotechnic devices such as flares. For example, in 2003, a federal district court in California found that the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) applied because perchlorate is ignitable and therefore a “characteristic”
hazardous waste
Hazardous waste is waste that has substantial or potential threats to public health or the environment. Hazardous waste is a type of dangerous goods. They usually have one or more of the following hazardous traits: ignitability, reactivity, co ...
.
See also
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References
Further reading
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External links
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{{Artificial light sources
Association football culture
Chinese inventions
Distress signals
Emergency communication
Gunpowder
Incendiary weapons
Lighting
Maritime safety
Missile countermeasures
Pyrotechnics
Military history of the Song dynasty
Wildfire suppression equipment
Military history of the Yuan dynasty