The hottest flame is violet on the color spectrum and white in the visible spectrum. The type of fuel and impurities, in addition to the flame temperature, contribute to the color of the flame.
The heat from fire is dependent on the type of fuel being burned and the chemical reaction that is taking place as a result as the fuel reacts with oxygen. The fuel itself becomes a gas during the burning process and breaks down into smaller molecules, ions, atoms, and free radicals. Some gases that result from burning include
- Carbon dioxide (CO2)
- Methyl (CH3)
- Hydrogen cyanide (HCN)
- Water vapor (H20)
Once the gas forms, combustion occurs as the various molecules react with oxygen to produce the heat and light known as fire. The ordinary color spectrum of fire spans the range of relatively cool to very hot, which is described by the acronym ROYGBIV in relation to the color spectrum:
Red is considered a relatively cool fire, where violet is considered very hot. To the naked eye, the first visible flame is typically a dull red while the hottest flames are white. Red flames can be from 500 to 800 degrees Celsius, while white flames can be 1,600 C or more. It is important to note that color is not always a determinant of temperature, since certain chemicals may burn hotter.