Firefighters helpless in Colorado wildfires

LAKE GEORGE, Colo. -- One thing is certain as wildfire sweeps across Colorado: Nature rules.

Five hundred firefighters only can watch in helpless amazement as miles of evergreen forest erupt in an orange blaze that is bearing down on suburbs southwest of Denver and mountain villages.

Fire behavior specialists say an air force of tanker planes and helicopters can't contain its terrible march without a big improvement in the hot, dry weather. Fire crews won't be risked on the front lines of a turbulent juggernaut that some experts compare to the Yellowstone fires of 1988.

"We cannot fight Mother Nature," Interior Secretary Gale Norton said while visiting the fire line of the biggest blaze, the Hayman fire, which has blackened 136 square miles since Saturday. It is among several fires across the state that have consumed a total of 234 square miles; another large fire burns 200 miles away in New Mexico.

Scientists like to say that all fire is the same, whether it's a lighted candle on a birthday cake or a wildfire crowning in a 200-foot Ponderosa pine tree.

That's true, technically speaking. A fire is a chemical reaction that requires fuel, heat and oxygen. Firefighters try to eliminate one of those essentials to extinguish flames. But a birthday candle isn't filled with tons of resinous pine sap that burns like kerosene.

Nor does its gentle flicker create its own weather and sweep up a mountainside.

In a wildfire, combustion releases hot gases and particles that rise in a column into the atmosphere -- 30,000 feet high in the case of the Hayman fire. The fire creates its own wind as fresh air rushes in to replace the rising air. A large fire can generate hurricane-force winds of 120 mph.

This propels the fire up the steepest mountain slopes. Even without direct contact with flames, this convective uplift can dry out, preheat and, in extreme cases, ignite plants in front of the wall of flames. The steeper the slope, the faster a fire will move and the hotter it will burn. A fire on a 30-degree slope will spread twice as fast as a fire on flat ground.