In Episode 8, check out UL's Fire Safety Research Institute's Dan Madrzykowski, as he explains why firefighters should keep the wind at their back:

When entering a structure or initiating fire attack, knowing the wind direction is a critical fireground factor. Winds greater than 5 mph will directly affect the rate at which the fire develops and potentially jeopardize the safety of advancing crew(s).

Knowing whether the wind is at your back or against you is a key size-up factor. Entering into the wind is like fighting your way down a chimney. As winds increase, fire growth and speed of spread will increase, too.

Watch this additional video showing a computer simulation of a wind-driven basement fire that resulted in a line of duty injury. This was developed at NIST, by authors currently employed at the Fire Safety Research Institute.