Fire
Fire is very hot and bright, and it consumes what it burns. This much we learn in childhood. Flames seem to be very weird, mysterious things, constantly moving and so, like water--which, interestingly, can put out a fire--campfires or fireplace fires are fascinating to watch. But the flames of a fire are simply a hot, glowing gas, and not, contrary to a common conjecture, plasma.
Scientific explanation
The flames of a fire are the result, or side-effect, of an exothermal (heat-producing) chemical reaction between oxygen and a fuel source (wood, or gasoline, for example). In this reaction the energy produced is released in the form of heat. The typical events in the creation of fire are as follows:
- a fuel source is affected by heat until it reaches its ignition temperature
- oxidation occurs; oxygen molecules break down larger molecules into carbon dioxide and water vapour
- this reaction produces a visible, incandescent (glowing) body of heated gas which sustains the reaction until either the fuel is expended or there is no more oxygen available to the reaction
In order for any fuel source to ignite from the presence of a heat source, it must reach its flash point, or the lowest temperature it can reach before becoming a combustable fuel-air mixture. The lower the flash point, the easier the fuel is to ignite. Because of this, all fires do not burn at the same temperature; some are hotter than others. The fire point is the temperature at which the fuel supports continuous burning[1] and is often a few degrees hotter than the flash point.
As long as all three properties of heat, oxygen, and fuel are present a fire will continue to burn. Removing any one of these elements will either remove the ability for a fire to start or will extinguish it.
Characteristics
Because fire is an observable effect, the varying properties can be identified. The height of the flame, for example, is usually dependant on the heat release rate of the fuel (the heat available or released(intensity) per square space, usually measured in Kw(Kilowatts) or Mw/sq.m.(Megawatts per square meter)) and the available oxygen consumption given the location of the fire.[2].
The color of fire can also be different depending on the type of fuel present in the reaction. Butane and Propane usually produce a blue hue when burning, whereas wood fires are usually yellow in color.
In the context of solids, liquids and gasses, fire or flame is mostly a gas, but one which has been ionized. In the volume of fire, gaseous CO2 and other compounds are raised into the air, along with the photons that emit light from the chemical reactions taking place. In different color fires, more oxygen exists in the reactions, speeding them up. This higher reaction rate produces an environment with a higher temperature, which means less compounds are rising into the air, and consequently less photons are being emitted.
Ultimately, what we see is the light produced from these reactions.
History of human use
It is hard to say when or where fire was first observed or discovered. Evidence from an excavation in the Benot Ya'aqov region of Israel have turned up burned fragments of flint and wood[3] that date from the Acheulian culture(1.8 mil. to 250,000 years ago), are some of the earliest available records of fire use in Eurasia. Evidence in the form of burnt bone in Africa was additionally discovered in 1986 when Bob Brain discovered a deposit approximately 6 meters thick in Swartkrans[4][5]. This finding possibly predated by a million years a discovery in Zhoukoudian, China, associated with Peking Man (H. erectus) circa 400,000 years ago[6]. Whenever it was actually discovered, fire was an integral part of human culture and survival.
Fire in culture
Since its discovery, fire has always been considered a powerful force in the eyes of mankind. In early cultures and civilizations, fire was held in such a high regard that gods and goddesses were worshipped as flame keepers. In the Greek and Roman civilizations, Hephaestus (Roman name: Vulcan) was the god of fire and the forge, and his icons were the anvil and the forge. The Egyptians worshipped Ra, the god of the sun.
Fire also plays a big role in symbolism, often representing a state of destruction and rebirth, as in the case of the Egyptian Phoenix, a mythical bird that at the end of its life perishes by flame, and rises again from its own ashes. In many religions, candles are used throughout ceremonies as a symbol of light, and in the bible, God speaks Moses through a burning bush.
Additionally, fire can be an implement or a requisite as a part of a celebration. In the United States, gunpower and chemical-based charges known as fireworks are launched to commemorate its Independance Day.
Uncontrolled fires
Despite mankind's ability to harness the power of fire, it still remains a wildly destructive force, in the form of forest fires and fire emergencies. The energy produced by fire has a variety of uses in manufacturing and production, entertainment, and in research and development. However, this same energy has been the cause of natural disasters that accrued over $1 Billion USD in costs[7], making up as much as ten percent of the total natural disasters between 1980 and 2006[8]. Additionally, the impact that fires can have has resulted in major losses throughout the 19th-21st centuries[9]. A few of the deadlier fires in the U.S. included The Great 1906 San Francisco Earthquake and Fire, The Great Chicago Fire, Los Alamos Wildland Fire, and The MGM Grand Hotel Fire in Las Vegas.
In the event of these emergencies, Fire departments, branches of the military, and other "First Responder" agencies are set up to respond as quickly as possible to fires that threaten human life and property. Unfortunately, fires like the Zaca Fire in California, can be large enough [10]that they can make containment difficult in short periods of time.
References
- ↑ Glossary of Terms. U.S. Department of Labor: Occupational Safety & Health Administration (May 1996). Retrieved on 2007-08-12.
- ↑ Jones, Sr., Barry R. CFI (05-18-2003). FAQ - Fire and arson, explosions, fire science, forensic engineering, and other fire related topics. Retrieved on 08-10-2007.
- ↑ Barach, Jerry (2004-04-30). Earliest evidence of use of fire in Eurasia discovered in Hebrew University Excavations at Benot Ya’aqov. Retrieved on 08-09-2007.
- ↑ Armstrong, Sue (1994). "South Africa - The Missing Pieces". New Scientist: 33.
- ↑ Levin, Eric (2005). "First Campfire Discovered in South Africa". Discover: 44.
- ↑ Weiner, Steve et al (1998). "Evidence for the use of fire at Zhoukoudian, China". Science 281: 251-253.
- ↑ 1980-2006 Billion Dollar U.S. Weather Disasters (Chronological - PDF). NOAA's National Climatic Data Center (2007). Retrieved on 2007-08-12.
- ↑ 1980-2006 Billion Dollar U.S. Weather Disasters (by State - PDF). NOAA's National Climatic Data Center (2007). Retrieved on 2007-08-12.
- ↑ 25 largest fire losses in U.S. history (in 2004 dollars). National Fire Protection Agency (2007-04-06). Retrieved on 2007-08-12.
- ↑ Zaca Fire General Information. California Department of Forestry & Fire Protection (2007-08-13). Retrieved on 2007-08-13. To date, 94,552 acres have burned, with 44% containment. The fire began on 4 July 2007, and is expected to be contained in September of 2007.