Wetness of fuel

When an object is in equilibrium with the surrounding humidity, it is considered to be “dry”. Such an object is readily combustible. If an object has excess water, the excess water has to be evaporated from it before it can be raised to its ignition temperature. Thus extra heat must be applied to wet fuel for it to ignite especially in the case of water since its latent heat of vaporization is 2260kJ/kg. Fuel that is wet internally ismore difficult to burn compared to fuel moistened on the surface only. The reason why all the water has to be evaporated is because the water vaporizes at a temperature that is well below the substance’s ignition temperature thus maintaining the low temperature of the fuel until all the water is evaporated.

Wind

The effects of wind on a fire mainly affects wildland fires but can also affect the spread of fires indoors if the wind is big enough. In wildland fires, the wind plays a pivotal role in the direction of the fire and the area of greatest fire intensity. The wind also pushes heat ahead of the fire, causing the fuel to dry out faster thus facilitating the advance of the fire. In a building, wind from open doors can promote more horizontal spread of the fire than expected on fire dynamics alone.