A magnesium torch is a bright light source made from magnesium, which can burn underwater and in all weather conditions. They are used for emergency illumination for railroad applications. They were also used in the 1950s up to the early 1970s as a light source for scuba diving, and were featured occasionally in television shows. 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.
Magnesium is highly flammable, burning at a temperature of approximately 3,100 °C (3,370 K; 5,610 °F), and the autoignition temperature of magnesium ribbon is approximately 473 °C (746 K; 883 °F). It produces intense, bright, white light when it burns. Once ignited, magnesium fires are difficult to extinguish, because combustion continues in nitrogen (forming magnesium nitride), carbon dioxide (forming magnesium oxide and carbon), and water (forming magnesium oxide and hydrogen).
Details may vary depending on the application. For railway emergency lighting and signalling purposes, the torch may consist of 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.
- All-weather emergency lighting
- Carrying the Olympic Flame from 1930 to at least 1984
- Underwater light source (obsolete) from the 1950s to the early 1970s.
- 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 sandbox video game, created by combining a torch with magnesium on a crafting table.
- Featured occasionally in the Sea Hunt television show.
- Magnesium torches were used in the The Undersea World of Jacques Cousteau documentary series. "The Secrets of the Sunken Caves" (episode 17, released in 1971) features the divers using these torches to explore a deep underwater cave.
- Dive light – Light used underwater by a diver
- List of light sources – Devices and processes that produce light
- Flare – Pyrotechnic light source
- "At which Olympics did the torch lighting ceremony first appear?". The Courier. Vol. 102, no. 180. Prescott, Arizona. 31 July 1984. p. 19.
- Dreizin, Edward L.; Berman, Charles H. & Vicenzi, Edward P. (2000). "Condensed-phase modifications in magnesium particle combustion in air". Scripta Materialia. 122 (1–2): 30–42. CiteSeerX 10.1.1.488.2456. doi:10.1016/S0010-2180(00)00101-2.
- "Magnesium (Powder)". International Programme on Chemical Safety (IPCS). IPCS INCHEM. April 2000. Retrieved 21 December 2011.
- "Magnesium Torch". www.fcsrail.com. Retrieved 31 July 2022.
- Hopkins, George Milton (1911). Experimental Science : Elementary, Practical and Experimental Physics. Vol. 2 (27th ed.). New York: Munn and Company Inc. p. 291.
- Schroeder, V.; Holtappels, K. Explosion Characteristics of Hydrogen-Air and Hydrogen-Oxygen Mixtures at Elevated Pressures (PDF). conference.ing.unipi.it.
- Stephen Elford (18 August 2022). "How To Make Underwater Torches In Minecraft?". Or-Live.
- Jacques Cousteau (26 September 1971). The Secrets of the Sunken Caves. Event occurs at 40:10.
- Sea Hunt re-enactment showing the user of underwater magnesium torches at the 7-minute mark
- Stock image of a scuba diver with a magnesium torch
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