Relative humidity impacts fire behavior by increasing or decreasing fuel moisture, which will affect flame length, rate of spread, energy released, amount of smoke produced, and whether or not the unit will even burn.
A backfire is a fire that burns into the prevailing wind, it is typically slow moving with shorter flame heights and lower fire intensity. Headfires are fires that burn with the prevailing wind; they are the fastest moving fire type, with the longest flames and greatest intensity. Flank fires are fires that burn or spread parallel to the prevailing wind direction; their behavior is between that of a backfire and headfire.
This is some type of break or barrier on the boundary of the burn unit that aids in containing the fire. Firebreaks delineate the boundary of the burn unit, allow for vehicle access around the unit and reduce the intensity of the fire along the edge. Firebreaks can be mowed lines, bareground lines made by dozing, grading or discing, or natural barriers such as creeks, cultivated fields, vegetation changes or roads.