Inside the burning building, it is so hot you can see the heat.

The room soars toward 800 degrees Fahrenheit, nearly four times the temperature at which water boils. Even wearing 65 pounds of fire-resistant gear, it feels hotter than a desert afternoon, and that's while lying on the floor.

The soaring flames, a fire official explains through his oxygen mask and several feet of smoke, aren't the main predator in this cauldron; instead, they are the catalyst. An unprotected person in a nearby room likely would be dead, having fallen victim to poisonous gases, smoke and the sweltering heat.

"It doesn't seem that bad right now, but there's no way you could survive this," Capt. Steve Kersse says, warning that when firefighters douse the flames, the ensuing roll of steam can be more dangerous than anything else in the room. "Just stay close to the ground, because it's even hotter up there."

Up there was a layer of hot air that seemed to have a life of its own, moving and expanding amid the fire and smoke that was quickly filling the room. Smoke, like wispy storm clouds, moved eerily under a sea of heat, hovering at chest level--an ominous sight that only a firefighter gets to see.

Last Wednesday, the Prince William County Fire and Rescue Department staged several infernos for its approximately 20-member recruit class, a training session aimed at exposing the newest members of the county's firefighting team to the realities of blazes. Fire officials also gave reporters a tour through the blazes, providing an unusual opportunity to see a raging fire from the inside out.

The blazes were set in a cinder block house at the county's Public Safety Academy in Nokesville, a facility designed to give recruits an experience that is as close to fighting a real fire as possible. Officials set wood pallettes, boards and sawdust on fire and then let the recruits go to work.

Simulating an actual response, firefighters arrive on the scene in ladder trucks and pumpers, quickly tying into the hydrant system and setting up various hoses. In one scenario, a car has apparently hit a town house and burst into flames, setting the building ablaze as well. Firefighters work to put out the fire and to rescue victims, doing meticulous searches even as the environment becomes increasingly hostile.

Without question the fires are real.

"This is definitely the most exciting part of the training," said recruit Kenneth Nesmith, 20, of the District. "You can do only so much in a classroom. There's nothing like going in and realizing that that was what the book was saying. There is nothing like feeling the heat."

Nesmith was talking about the radiant heat that spreads from the source of the fire and then collects within a building, combining with toxic gases generated when objects inside burn, producing a very deadly mix. An unprotected person would die quickly. Firefighters, on the other hand, wear a full array of gear--fireproof pants, jacket, gloves, helmet, a hood similar to a ski mask and an oxygen tank, all weighing a total of about 65 pounds.

Although the gear affords firefighters great protection, it has its limitations. Firefighters still can feel the heat of a blaze. Sight is limited, and conditions can be catastrophic.

Fire and Rescue spokesman Steve Strawderman, who led reporters through the burning building, said that even with the gear there are significant dangers, such as buildings that are near collapse or fire flashovers that can disable or kill firefighters.

Strawderman said firefighters are often thrust into unknown circumstances and in some cases will let a building burn if a situation appears to be too dangerous. He said firefighters have to gauge risk factors before deciding to enter a building.

"We will risk a lot to save a life," Strawderman said during Wednesday's presentation. "We will risk a little to save property, and we will risk nothing to save nothing. That's how we operate."

Given the unpredictability of fire, which often seems to have a life of its own, Strawderman said firefighters are constantly faced with risk, on almost every call. In fiscal 1999, the department's 229 uniformed officers reponded to more than 5,800 fire incidents--an average of almost 16 fires each day.

"In a way, that's what's exciting about it," said Nesmith, who had wanted to be a firefighter since he was a child. "Your heart beats faster than normal. Everyone knows that fire is unpredictable; you never know what it's going to do. That's why we practice, so you just stay alert and don't get complacent, because that's when accidents happen."