From the Introduction ... 'It is a well known fact that the presence of moisture exerts considerable influence on the difficulty of ignition and the subsequent rate of combustion of forest fuels. Its effect on ignition is primarily a result of the fact that the water must be heated to the Boiling Point and then vaporized before the fuel will reach its ignition temperature. If enough moisture is present the heat required may be greater than that available in the firebrand, and ignition will not occur. Once ignited, water must be continuously driven from adjacent fuels, if the fire is to spread. This absorbs some of the heat energy which is emitted by the fire and reduces the rate of combustion. It is also possible that the presence of moisture affects combustion due to the water vapor which surrounds the fuel and dilutes the available oxygen.The correlation between fire behavior and fuel moisture is an important part of every fire danger rating system in use today. In every system, measurements of certain factors which are presumed to influence fuel moisture are made. These are, in turn, correlated with fire behavior to produce the desired index.'