A magnesium torch is a bright light source made from

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...

, which can burn underwater and in all weather conditions. They are used for emergency illumination for railroad applications. They were also popular in the 1950s as a light source for

scuba diving Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface air supply. The name "scuba", an acronym for "Self-Contained Underwater Breathing Apparatus", was coined by Chri ...

, and were featured occasionally in the ''

Sea Hunt ''Sea Hunt'' is an American action adventure television series that aired in syndication from 1958 to 1961 and was popular for decades afterwards. The series originally aired for four seasons, with 155 episodes produced. It stars Lloyd Bridges a ...

'' television show. A relay of magnesium torches was used to transfer the Olympic flame from Greece to the site of the Olympic games several times since the first occasion at the 1936 Berlin Games.

Function

Magnesium is highly flammable, burning at a temperature of approximately , and the

autoignition temperature The autoignition temperature or kindling point of a substance is the lowest temperature in which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to s ...

of magnesium ribbon is approximately . It produces intense, bright, white light when it burns. Once ignited, magnesium fires are difficult to extinguish, because combustion continues in

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...

(forming

magnesium nitride Magnesium nitride, which possesses the chemical formula Mg3N2, is an inorganic compound of magnesium and nitrogen. At room temperature and pressure it is a greenish yellow powder. Preparation * By passing dry nitrogen over heated magnesium: ...

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

(forming

magnesium oxide Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ...

and

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

), and water (forming magnesium oxide and hydrogen).

Structure

Details may vary depending on the application. For railway emergency lighting and signalling purposes, the torch may comprise a rolled cardboard structural tube with plastic end covers, one of which may be the ignition device. The fuel is inside and exposed by removing the top end cap. This type of construction may be unsuitable for underwater use.

Uses

*All-weather emergency lighting *Carrying the

Olympic Flame The Olympic flame is a symbol used in the Olympic movement. It is also a symbol of continuity between ancient and modern games. Several months before the Olympic Games, the Olympic flame is lit at Olympia, Greece. This ceremony starts the Olymp ...

from 1930 to at least 1984 *Underwater light source (obsolete) in the 1950s. *Photographic illumination (historical), using a somewhat different form of torch.

Hazards and safety precautions

Underwater use produces large volumes of hydrogen gas, which if trapped in a confined space with exhaled breathing gas, which typically contains more than 17% oxygen by volume, can form a flammable or explosive gas mixture. The range of explosive mixtures of hydrogen and air or oxygen is unusually wide, but varies with temperature, pressure and other factors. A magnesium torch does not necessarily give warning of an atmosphere that cannot support life or consciousness, as it continues to burn underwater, or in an oxygen free atmosphere if sufficient nitrogen or carbon dioxide are present.

In popular culture

* An underwater torch is available in the Education Edition of the ''

Minecraft ''Minecraft'' is a sandbox game developed by Mojang Studios. The game was created by Markus "Notch" Persson in the Java programming language. Following several early private testing versions, it was first made public in May 2009 before bein ...

'' sandbox video game, created by combining a torch with magnesium on a crafting table. * Featured occasionally in the ''

'' television show.

External links

''Sea Hunt'' re-enactment
showing the user of underwater magnesium torches at the 7-minute mark

of a scuba diver with a magnesium torch

References

{{Artificial light sources Diving equipment Light sources History of underwater diving