A thousand firefighters worked doggedly in 100-degree heat Thursday to snuff what officials said was the nation's fastest-growing fire in the past decade.

A wind shift Thursday night pushed a wildfire that started Tuesday near northern Hanford back on land that had already burned and was welcome news to firefighters. Firefighters have switched to a defensive mode, meaning their focus now is on containing small, scattered fires, officials said.

But despite the better outlook, the fire has already burned about 300 square miles of sage and grass, destroyed rural homes in Benton City and raged across a third of the Hanford nuclear reservation.

The scorched land included a large portion of the newly designated Hanford Reach National Monument, where firefighters were restricted by federal law from bulldozing fire lines, bringing in their largest firefighting trucks and taking other measures that would have destroyed the fragile shrub-steppe land.

Early Thursday evening, fire officials were nervously watching weather reports -- hoping winds would not rise above the 30 mph gusts predicted.

If that was the worst weather to hit, firefighters were confident they could hold what remained of their fire line. But they knew a sudden, unexpected change in the wind had caused the fire to roar out of control the day before, just when they thought it was nearly contained.

In a few hours late Wednesday night and early Thursday morning, the fire incinerated 20 homes north of Benton City and destroyed 53 other buildings, including sheds, garages and shops, most of them also near Benton City.

Firefighter John Evans drove by his Acord Road home late Wednesday in a fire truck, fresh from fighting the fire near the Silver Dollar Cafe and "saw huge fireballs coming off it."

"I was tore up," he said. "My heart just sank."

However, the most feared scenario, which had the eyes of the nation on the Tri-Cities, did not occur.

The fire burned across three old radioactive waste sites at Hanford, but no radiation releases were detected. Many Hanford buildings and reactors are protected from wildfire by wide perimeters of gravel, and more fire breaks were being bulldozed Wednesday and Thursday.

The state Department of Health was monitoring air samples Thursday and taking vegetation samples.

"We're not going to let the Department of Energy get away with anything if we find anything positive," said Al Conklin, head of the Department of Health's division of radiological protection.

One Benton City resident, Robert Pierce, 49, had burns covering 25 percent of his body, mostly on his back and arms, said Larry Zalin, spokesman for Harborview Medical Center in Seattle. Pierce was listed in critical condition in the hospital's intensive care unit Thursday morning, but his condition had improved to serious by afternoon.

Fire officials still weren't sure Thursday night how Pierce was burned. He staggered out of the smoke the night before and collapsed on a roadway in the area where houses were burning north of Benton City.

At least 13 other people were treated for smoke inhalation at Tri-City hospitals, and one firefighter was treated for a minor leg injury.

Fire officials were thankful late Thursday that injuries were not worse.

"We almost lost two deputies and a citizen," said Glenn Johnson, the Richland fire chief who was acting as fire coordinator for Benton County.

Two Benton County deputies came close to being trapped in the fire as they rescued an elderly Benton City woman from her home, Johnson said. Fire surrounded her house as they got her into their car, so they drove off cross-country through nearby yards to get away from the fire.

Ironically, just a few hours before the fire raged into Benton City it appeared to be almost under control.

Firefighters thought they'd almost knocked down the fire late Wednesday afternoon and had a backfire set. They had as little as 300 yards of the perimeter of the fire still burning.

But then the wind shifted.

"We got caught completely off guard," Johnson said. The fire roared down the east side of Rattlesnake Ridge. At the horn of the Yakima River -- a U-shaped curve between Benton City and West Richland-- it split in two.

Some flames moved toward Richland, then crossed Highway 240 and moved back onto the Hanford reservation. That wing of the fire may have taken out two outbuildings, but did no other damage to buildings. There had been erroneous claims Wednesday night that two homes were destroyed in the Horn Rapids neighborhood just south of there.

Some of the fire also jumped the river at the horn, and firefighters put out flare-ups near Harrington Road, but it did not spread there.

Another wing of the fire raged toward Benton City, covering 20 miles in just 90 minutes.

Marty Peck, who lives just north of Benton City, said he was eating dinner beside his backyard pool Thursday night, watching the flames in the distance beyond his pasture.

But as the flames began to race down nearby Rattlesnake Mountain, his family grew concerned. Then, without warning, "the pasture just exploded in flames," he said.

He and his mother jumped in his car, but the smoke was so dense he couldn't find his way out of his own driveway without hitting a pole and the ditch.

Thursday afternoon, Gov. Gary Locke visited Peck and others who had lost their homes along Acord Road.

"Hang in there. Let us know what we can do to help," Locke said.

Nothing but twisted metal remained of the Pecks' mobile home as Locke watched Franklin County District 3 firefighters search through the rubble for hot spots and salvageable belongings.

Then Peck showed Locke the firefighters' most precious -- and amazing -- find.

His father had died just a few months ago, but firefighters had somehow found his blackened wedding ring among the ashes.

"This will make (my mother) very happy," Peck said.

A few houses down Acord Road, Evans was surveying the damage at the home he'd shared with his parents and other family members. The main home, surrounded by green grass, remained. But a second home where his sister and brother-in-law lived, a shop, two sheds and his classic '64 Ford truck were destroyed.

He said his mother had seen the fire coming over the hill behind their home "and five minutes later the neighbor's house was on fire."

Many of the homes that had been saved were surrounded with green, well-watered lawns and were clear of cars, machinery and the other flotsam of rural life. Some homes were destroyed while others just yards away on either side looked untouched.

"More than anything, you can just tell the devastation, the despair, the shock in the eyes of the homeowners," the governor said.

The governor also met with firefighters, thanking them for their round-the-clock work, and he planned to talk with local officials.

"We want to see what their costs are, what the needs are and see if we can make a federal claim," he said. "We need to find the extent of the damages and what we can do to help."

Energy Secretary Bill Richardson also was scheduled to arrive in Richland near midnight Thursday.

Those who had homes to return to Thursday night were back in their own beds, after many had spent the night in shelters at churches or schools in Prosser and the Tri-Cities on Wednesday.

Fire officials had ordered as many as 7,000 people to evacuate their homes. That included everyone in Benton City and nearby rural areas, part of northern West Richland and Richland's Horn Rapids neighborhood.

National Guard officers were assigned to patrol the evacuated area near Benton City, but many people refused to leave.

"There were some holdouts who were going to hang out in their homes no matter what," said Nancy Aldrich, mayor pro tem of West Richland. "But we kept those addresses, knowing ... where to find them in an emergency."

Horn Rapids and West Richland neighborhoods were reopened Thursday morning, and shortly after noon Benton City residents were allowed to return to their homes.

Firefighters Thursday evening were still battling spot fires and a larger fire at the 200 Area of Hanford, where underground tanks hold radioactive waste and contaminated chemical plants sit ideal. Fire officials said 160,000 of the 190,000 acres that had burned were on the Hanford site.

That included land on the west side of Hanford that makes up more than a third of the new national monument. It has been left largely undisturbed since the 1940s, when it was fenced off as a wide security buffer around Hanford.

"The fire was fought (there), but there were stringent rules," Johnson said. "There were resources on it from the moment it occurred."

However, firefighters tried to stay on roads and trails where vegetation was already destroyed and used wildland fire trucks, which included some smaller and lighter vehicles.

Sagebrush takes decades to regenerate, and bare land can easily be overtaken by noxious weeds.

Elsewhere at Hanford, firefighters were attacking the fire more aggressively. Bulldozers and farm disk harrows were used to dig the fire line down to bare earth.

Three air tankers dropped retardant, although it was a slow process. East Wenatchee and Redmond, Ore., were the closest places to pick up a new load of the chemical after a drop.

Eight helicopters also were available, either to survey the fire or to drop water scooped out of the Columbia River.

Firefighters came from 18 counties, plus several federal agencies, to fight the fire. Federal officials had designated the blaze as the top fire priority in the nation, said Tom Cole, state operations chief with Washington state's emergency response team.

"We've had some very tense hours," said Keith Klein, Hanford manager for the Department of Energy. However, lighter winds Thursday provided a major break for the fire team, he said.

The firefighting operation could begin to ramp down this afternoon, he said..