A fire tetrahedron is a solid pyramid with four plane faces, each representative of the four necessary elements for starting a fire.
For many years, it has been widely accepted that the combination of the following three (3) factors contribute to the initiation of a fire:
- a source of ignition/energy/heat
The combination of all these three (3) factors has therefore led to the widely known Triangle of Combustion. Consequently, when trying to put out a fire, we strive to remove at least one of these three components
Picture 1 - Fire triangle
Further research over the years revealed a fourth necessary component of fire, the chemical chain reaction. The Fire Triangle was consequently transformed to the Fire Tetrahedron. Put it simply, a Tetrahedron is a solid pyramid with four plane faces (from the Greek words ''tesseris edres''), each one representative of the four necessary elements.
In short, a fire begins by an external ignition source which is usually in the form of a flame or spark. With its turn, the external ignition source heats the fuel under the presence of oxygen. As both fuel and oxygen are heated, molecular activity increases. If properly heated, a self-sustaining chemical reaction is developed. The consequent chemical reaction will then escalate at a point where the external ignition source is no longer necessary for the propagation of the fire.
Once ignition has occurred, it will continue until:
- all the available fuel has been consumed or
- the fuel and/or oxygen is removed or
- the temperature is reduced by cooling or
- the number of excited molecules is reduced and the chain reaction is broken
Picture 2 - Fire tetrahedron
Although simplistic in nature, presented diagrams are in fact a good example of how to actually extinguish a fire in the real world. For example, we can create a barrier using foam in order to reduce/eliminate the ''fueling'' of fire and therefore deprive the fire from one of its necessary elements (oxygen). By applying water, we can also reduce the temperature below the ignition temperature. Finally, by using a Halon extinguisher, we can create an inert gas barrier which will interfere with the chemical chain reaction.
Related Standards and Codes
There are various international standards referring to fire protection. Most widely used standards nowadays are National Fire Protection Association (NFPA) standards. However, reference can also be made to other US standards (like ANSI standards or Code of Federal Regulation (CFR) standards) or European standards (ISO and DIN standards). Leading commercial insurance companies have also developed standards of their own (for example Factory Mutual) and their requirements may sometimes be stricter than those of international standards.