Burning Brush in Beaumont, Calif.

The deadly Esperanza wildfire in southern California killed four U.S. Forest Service firefighters Thursday; a fifth remained alive on life support. Fueled by winds gusting to 40mph, the fire burned through 24,000 acres, adding to a record U.S. wildfire season. So far this year, fires have burned 9.4 million acres, topping 2005's record of 8.6 million acres, according to the National Interagency Fire Center.

The four firemen of Engine Crew 57 died Thursday morning as they fought to save a house from onrushing fires near Twin Pines, Calif. Engine Capt. Mark Loutzenhiser, 44, left five children. Also killed were Jess McLean and Jason McKay, both 27, and Daniel Hoover-Najera, 23. Pablo Cerda, 23, lay in critical condition in a local hospital with burns over 90 percent of his body. Doctors called his prognosis poor. The four fatalities were the worst single episode in California since four firefighters died in 1979 in a fire in central California.

The Esperanza fire was fueled mostly by chaparral, dense scrub wood that resides in steep, semiarid country. It is highly flammable and difficult to fight, according to Ken Pimlott, an assistant deputy director of the California Department of Forestry & Fire Protection, who spent years fighting fires in southern California. He spoke to NEWSWEEK's Andrew Murr about the challenges of chaparral fires. Excerpts:

NEWSWEEK: Why are chaparral fires so dangerous?

Ken Pimlott: For a number of reasons. For one thing, the chaparral plant community is very flammable. It's a combination of a number of plant species like manzanita and chamise whose leaves are covered with a waxy coating that holds in water, but it is very flammable. And as those plants mature, there's a significant dead component within the plants. It's basically kindling wood inside the flammable waxy material. Then you get into the wind conditions we're having right now: the Santa Ana winds. They are warm and dry winds that blow off the desert. When those wind blows, it dries down the vegetation even more. The relative humidity of the air can get into the single digits, 5 to 10 percent, and the fuel moisture level gets down to around 3 percent. They are very strong. They blow up to 40 or 50mph, and they create a very fast-burning, high-intensity fire.

It's been reported that the Esperanza fire overran the firefighters. How fast can these fires move?

They can move up 5 or 6mph under the right wind and fuel conditions.

A person could outrun a 6mph fire, couldn't they?

You have to look at the circumstances. If you were running across flat ground, certainly. But these fires are burning in very steep terrain, with holes and brush into your way. And you are wearing full gear, which is heavy. There is no way you are going to be running very fast.

The fires change direction quickly can't they?

Absolutely. There are key things that move the speed and direction of a chaparral fire. It'll burn upslope faster, because that flame preheats everything above it. Then of course wind direction. If the wind is also blowing uphill, you are going to be amplifying the speed of the fire. And as the fire grows in heat, you are getting a larger convective column, drawing in air and increasing the wind. That's how you get spot fires occurring sometimes a quarter mile or half a mile ahead of the fire because the burning embers are being lifted up and caught in the winds and blown downwind.

Your agency fights forest fires as well as grass fires and chaparral fires. What are the key dangers in fighting chaparral fires?

It's a lot more labor intensive to work in the heavy chaparral, or brush, fuels. It's a lot more difficult to move around because of the thick brush. And you have to cut through brush that is eight or 10 feet tall. If you are working in grass, it's light fuel. You can cut a control line much quicker. The key here is the intensity of the fire. Grass is the lowest. Brush can be very high. And timber can be the highest.

Do people consider chaparral fires more dangerous than other types?

We consider them all equally dangerous. Historically, we've had just as many injuries in light fuels such as grass as we have in brush. That's because folks can underestimate of the fire in grass. Fires move rapidly in the grass.

Are firefighting tactics different in chaparral?

They are. There are tactics you can't use in chaparral or brush. You can't mobile pump in brush. In grass, as long as you can drive around the perimeter, you can hose down the edge of the fire. Obviously you can't move your vehicles through heavy brush, so your tactics have to change. You've got to place your fire engine at a key noncombustible anchor point. You are going to have to physically lay hose through the brush to fight the fire. And then you have to use hand tools to cut the brush out of the way to make a fire line or a control line. So when you have people out in the brush, that poses a much greater risk.

How about the differences between chaparral and forest fires?

On a timber fire you have two kinds of fires. You have a fire in the under story—in the brush and smaller trees. Typically those are lower-intensity fires. And then you have a crown fire, where it gets up into the canopy, and runs through the canopy. In the crown fire, fire you are looking at timber falling. You are looking at very high heat output. We measure things in flame length, and in a canopy fire, you can get a flame length of 100 feet. And when are working there, you've got to look at falling timber overhead. And you can be burned over (where the fire overtakes firefighters and burns past them) in the timber, too.

When fires overtake firefighters, what do they do to save themselves?

There are basic things that are evaluated. Prior to that deploying, firefighters are going to evaluate their escape routes. They are going to have at least two routes of escape identified. They are going to post a lookout so that if the fire changes direction, they have someone identifying that. If escape routes are compromised, the last resort is they utilize the fire shelter. These are devices all firefighters carry with them as part of their safety gear. It looks like an aluminum pup tent designed for one person to get into. If there isn't another direction to go in, that's what you do. You have to do that in a clear location. The firefighter gets into it, and it allows the heat to be deflected.

Do we know if the men used those devices in this case?

I do not know. Obviously it's under investigation, and not much information is being released yet. It's hard to tell. The vehicle was badly burned, and that's another escape route. Folks are taught the vehicle can be used as a refuge. Hopefully, when this report released, we'll learn more about the situation and what the thought process was.