A truck hauling 34,000 pounds of highly explosive powder crashed in the Springfield interchange yesterday, forcing highway closures that crippled the region's road network from sunrise to sunset as emergency teams worked to remove the threatening load.

The speeding rig carrying black powder to an explosives factory in Vermont flipped off a ramp shortly before 4 a.m. More than 16 hours later, crews were still struggling to unload the cargo, avoiding sparks by working shoeless in static-free cotton clothing and with tools made of brass.

"It's like defusing a bomb," said Dan Schmidt, a spokesman for the Fairfax County fire department. "The procedures are in place, and you can't deviate from them one inch."

Authorities closed Interstate 95 north and a portion of the Capital Beltway after the crash, snarling the morning commute, and evacuated hundreds of nearby residents. Although officials later opened all but northbound I-95 while they mobilized to remove the powder, they closed the Beltway and surrounding highways just before the evening rush hour when they decided to proceed with the cleanup.

Officials said the danger of lightning strikes from possible thunderstorms prompted them not to wait until the commute was over. They also ruled out working at night because of the difficulty of seeing black powder in the dark and concern that using lights powered by generators or batteries could ignite the truck, said Fairfax County Police Chief J. Thomas Manger. The load was cleared and the roads reopened by 9 p.m.

Although no one was injured in the crash -- which police said was caused by reckless driving by the trucker -- it again demonstrated how vulnerable the Washington region's desperately overburdened road network remains even to isolated incidents.

"I've been living here all my life, and I'm pretty easygoing, but this is the worst," said Pete Owens, 38, anticipating a two-hour detour along Route 1 from Alexandria to his home in Woodbridge. He had spent four hours in traffic during the morning commute. "I could have murdered someone."

Though aware of the impact of closing the Beltway again, police said they would not gamble. They feared that the 680 50-pound boxes of powder -- intended for use in blasting slate in New England mines -- had been ruptured during the wreck. The powder is considered extremely volatile when exposed to heat, shock, friction or even static electricity and posed a threat too grave to leave unaddressed until after rush hour, officials said.

"The longer it sits there, the more of a concern it becomes," said Kenneth Jones, the county's deputy fire chief.

Nor could the Beltway remain open to traffic as squads investigated the interior of the truck and began to unload the contents.

"What happens if a spark goes off? It's not a pretty sight. It would be a big bang," said Virginia State Police Sgt. David Feather, who is in charge of hazardous material enforcement in Northern Virginia.

The material was deemed so incendiary that firefighters repeatedly doused the truck with water to avoid sparks and cool the cargo, which had been heating up under the intense sun since daybreak.

When the crews successfully opened the severely dented 20-foot steel container strapped to the flatbed truck, they inspected all the boxes and then resealed them for transport. Some had been crushed, but none had burst.

Scores of trucks, police cruisers and other emergency vehicles, from a variety of county, state and federal agencies including the Bureau of Alcohol, Tobacco and Firearms, crowded onto a grassy staging area along I-95. Alone across the ghostly interstate, in the oppressive heat and humidity, rested the uncertain threat of the capsized truck.

As the interchange known as the Mixing Bowl sat empty, the remainder of the region's road network had swollen nearly to the breaking point, with traffic observers reporting that some evening commutes had doubled and tripled in time.

"This is akin to the Wilson Bridge jumper last November that had ripple effects all across the region," said Steve Kuciemba, of the SmarTraveler traffic service, referring to the massive gridlock caused when D.C. police closed the Potomac River span at rush hour because of a man threatening to jump.

Kuciemba said that all the local roads in the southern portion of Fairfax County were gridlocked and that major backups were afflicting Interstate 66 as well as Maryland's part of the Beltway -- only hours after they had suffered mammoth tie-ups in the opposite directions.

The crash occurred just before 4 a.m., when the driver, Juanita I. Kirk, 41, of Phoenix, lost control of the rig as she was heading up the ramp connecting northbound Shirley Highway with the outer loop of the Beltway, both of which are labeled I-95. She told police that moments earlier, she had "heard a loud noise, pops."

When the rig flipped off the left side of the ramp, it became the latest casualty of the region's most treacherous interchange, an infuriating junction that has previously taken a toll on dozens of trucks that tried too quickly to navigate its sharp curves. State police said the truck appeared to be traveling over the 35-mph speed limit and charged Kirk with reckless driving.

A spokesman for the trucking company, Tri-State Motor Transit Inc., said Kirk and her boyfriend, Tod W. Johnson, 40, who was in the cab with her, were traveling from the port at Newport News, Va., where they picked up the load, and had been on the road for less than two hours.

James Wingfield, safety director of the parent company, TRISM, said Kirk had joined the company's subsidiary, Tri-State Motor Transit Inc., in December 1997 and received specialized training in handling and transporting hazardous materials at the firm's headquarters in Joplin, Mo. "It was my understanding her record was good," he said.

Oscar Rodes, president of Petro-Explo Inc, the Arlington, Tex., company that imported the explosives from Brazil for Cleveland-based Austin Powder Co., said the explosive was packed in plastic bags and stored in 50-pound quantities inside plastic-lined cardboard boxes. The boxes were then packed, according to U.S. Department of Transportation regulations, inside a 20-foot, wood-lined container, Rodes said.

Tri-State Motor Transit is one of the nation's main haulers of hazardous materials, running nearly 400 trucks and employing 800 drivers, according to the Department of Transportation. An estimated 75 percent of its revenue comes from hauling hazardous materials. During the last two years, the company's trucks and drivers have failed inspections at less than half the national rate, according to the Federal Highway Administration. They have been involved in 28 crashes over that period, the administration reported.

A Department of Transportation spokesman said that the truck had apparently been properly labeled as containing hazardous material and that the driver acted properly by immediately notifying state and federal officials about the contents after the crash.

Barely a half-hour after the crash, Fairfax County officials had approved a plan to evacuate the surrounding neighborhoods and began to order residents out of about 50 homes in the Trailside Park area an hour later.

Janice and John Apruzese, who live on Pinto Place, were asleep when police banged on their door.

"Don't get dressed. Just get out of here," police told the family, so John Apruzese, a physicist for the Navy, and his wife got Laura, 12, and Stephanie, 7, out of bed and headed to Lee High School a few blocks away.

There, people were already emerging bleary-eyed from their cars. Children scampered around the parking lot. Adults walked dogs, and teenagers preened for the television cameras. Principal Donald Thurston, like an anxious host, tried to find enough staff to rustle up breakfast for dozens of hungry people, offering them sausage and pancakes on a stick, juice and Trix cereal.

Classes were canceled at Lee, and many students at other schools arrived late because bus routes were disrupted, county school officials said.

Staff writers Victoria Benning, Alice Reid, Leef Smith and Graeme Zielinski and Metro researcher Bobbye Pratt contributed to this report.

Major Mess At Mixing Bowl

A truck with 17-tons of black powder overturned at the busy juncture of I-95, the Capital Beltway and I-395 yesterday. Both morning and evening traffic were affected.

When: Just before 4 a.m.

Where: On exit ramp from northbound I-95 to the outer loop of the Capital Beltway.

Contents: 34,000 pounds of powder destined for slate mining in Vermont.

Transport company: Tri-State Motor Transit Inc., hauling the load from Newport News, Va., to New Haven, Vt.

Injuries: None.

Driver: Juanita I. Kirk, 41, of Phoenix, charged with reckless driving.

Unloading begins: 4:10 p.m.

Last night's rush-hour closures: Beltway between Braddock Road and Van Dorn Street; I-95 between the Beltway and Franconia-Springfield Parkway; I-395 between Beltway and Edsall Road.

CAPTION: Workers from the Bureau of Alcohol, Tobacco and Firearms empty boxes of explosive black powder from the truck, which flipped off a ramp on I-95.

CAPTION: Truck driver Juanita I. Kirk, 41, was charged with reckless driving.

CAPTION: Cars are lined up as far as the eye can see on I-95 as the ripple effect of a truck crash snarls the region's highways.

CAPTION: A pair of Virginia state troopers confer amid a phalanx of emergency vehicles at the crash scene.

CAPTION: At Lee High School, Deputy Fire Chief Kenneth Jones talks to Maria Guanio, left, and John and Virginia Hare.