Final answer:
The traditional model known as the 'fire triangle' includes three elements necessary for a fire: heat, fuel, and oxygen. However, some modern references add a fourth element to form the 'fire tetrahedron,' which is the chemical chain reaction necessary for the fire to continue burning.
Step-by-step explanation:
In order for a fire to occur, four entities must be present at the same time. However, according to Smokeybear.com, three elements are traditionally known as the essential components for a fire: heat, fuel, and oxygen.
These elements form the 'fire triangle,' and each plays a critical role.
- Heat is the catalyst that initiates the fire and is necessary for maintaining the fire and enabling it to spread. It facilitates the fire's spread by drying out and preheating nearby fuel and warming the surrounding air.
- Fuel can be any combustible material and is characterized by various factors such as moisture content, size, shape, quantity, and how it's spread over a landscape. The fuel's moisture content determines how easily it will burn.
- Oxygen is required to support the chemical reactions during a fire. The air contains about 21 percent oxygen, and most fires require at least 16 percent oxygen content to burn. This component is critical for oxidation, which is when fuel burns and reacts with oxygen, releasing heat and producing combustion products.
Though not mentioned by Smokeybear.com, some modern fire science resources also refer to a 'fire tetrahedron,' which adds a fourth component called the 'chemical chain reaction.' This explains that a sustained chemical reaction is part of the process, which is crucial for the fire to continue burning.