July 19 (Bloomberg) -- New York City said tests of debris and dust from the area surrounding the site of yesterday's steam pipe explosion near Manhattan's Grand Central Terminal came back positive for asbestos.

City officials told people who work and live by the site of the blast to stay out of the area. Six of 10 samples of debris and dust taken from the area last night tested positive for the fire-retardant mineral, which has been linked to respiratory disease and cancer, while eight air samples tested negative, the city's Emergency Management Office said in a statement today.

``While exposure to asbestos over many years carries known health risks, the brief exposures that people may have experienced after last night's steam pipe break are not likely to cause long-term health consequences,'' city health officials said in a statement.

The explosion blew a 25-foot (7.6-meter) hole in 41st Street a block south of Grand Central, killing one person and wounding about 30 people, including three firefighters. The blast snarled traffic in midtown Manhattan during rush hour and halted subway service.

The 4, 5, 6 and 7 trains returned to a normal schedule this morning after earlier bypassing Grand Central, the city's busiest subway station. The 42nd Street shuttle was also back in operation after being suspended last night.

A ``frozen zone'' between 40th and 42nd streets and Vanderbilt and Third avenues will remain in place while asbestos testing continues, and individuals outside the area won't be allowed to enter, the Emergency Management Office said.

Streets Closed

Lexington Avenue remained closed between 34th and 57th streets. Third Avenue was closed between 38th and 42nd streets, while Park Avenue was shut from 34th Street to 54th Street and 42nd Street was blocked between Park and Third avenues. Contractors have begun a clean-up of dirt and debris, and Third Avenue will be reopened after electrical work is finished.

Thousands of office workers were blocked from reaching their buildings, with almost 4,000 stopped from entering the Socony-Mobil Building on 42nd Street between Lexington and Third avenues, where tenants include Pfizer Inc., American Airlines Inc. and international law firm Wilson, Elser, Moskowitz, Edelman & Dicker LLP, unless they had respirators.

Some Grand Central area businesses said they are losing sales because of the street closures. At Alex's Shoe Repair on 44th Street, near Madison Avenue, there was just one patron getting his shoes shined during the early morning rush hour.

``There is none,'' owner Alex Vakham, 59, said when asked how the blast was affecting business.

Commuting Headaches

About 400 Consolidated Edison Inc. technicians and contractors worked through the night to test debris and the air for asbestos, which may have been used to insulate the 83-year- old steam pipe.

The company today asked electricity customers in the eastern midtown area of Manhattan to conserve electricity because of power grid damage caused by the rupture. All customers had power, the company said. The affected area extended from the East River to Fifth Avenue and from 39th to 57th Streets, the company said.

Firefighters checked for structural damage in nearby basements, while city Buildings Department engineers inspected interiors of four nearby buildings and found water in basements. Six nearby structures had minor lower-level window damage.

Injuries Treated

New York-Presbyterian Hospital/Weill Cornell Medical Center treated 27 patients from the blast, the hospital said. One person was in critical condition, another was listed in serious condition and 25 were treated and released. A total of 18 patients were treated at Bellevue Hospital.

The New York City Police Department confirmed that a New Jersey woman was killed in the blast, although it declined to release her name pending the notification of relatives. The Associated Press reported the victim as Lois Baumerich, 57, of Hawthorne, citing police.

Health Department officials said people inside buildings near the blast should keep windows closed and switch air- conditioners to re-circulate to protect against the possibility of airborne asbestos.

``There is no reason to believe whatsoever that this is anything other than a failure of our infrastructure,'' said Mayor Michael Bloomberg at a press conference at the scene. Bloomberg said the explosion may have been caused by cold water that got into a 24-inch steam pipe that was installed in 1924.

Bloomberg, who earlier this morning was attended the funeral of a city police officer killed in a traffic stop, scheduled a press briefing for 5 p.m. local time.

Taking Precautions

Jessica Leighton, deputy health commissioner for environmental risk assessment, advised workers and residents to avoid contamination by washing themselves with soap and water. She said clothes exposed to the initial blast should be put in plastic bags and kept separate as a precaution against the possibility that asbestos has been released.

Burke told reporters last night it was too early to know the cause of the explosion. He said that water from heavy rains earlier in the day may have made contact with a hot steam pipe, causing it to rupture.

The blast occurred shortly before 6 p.m. a block from Grand Central, through which more than 700,000 commuters pass every day, sending plumes of steam and debris into the air and rattling the nerves of a city that is still recovering from the terrorist attacks of Sept. 11, 2001.

Streaming Crowds

About 40 minutes after the event, as a column of steam continued to rise above Lexington Avenue, crowds streamed north, jamming the sidewalks and walking in the street while lugging briefcases and talking anxiously into their cell phones.

Dean Brown, an attorney with LeSchack & Grodensky who commutes from Westchester County, was among those switching to the subway from Metro-North at 125th Street to get to his office downtown. He said he was meeting a friend for dinner at the MetLife Building adjoining Grand Central last night when the blast occurred.

``Everyone was panicked, everyone was on their cell phone,'' Brown said, recalling the experience of Sept. 11. On that day, he looked south from his office and saw an ``orange ball of fire'' after one of the hijacked planes smashed into the World Trade Center, then joined the crowds walking north to get to Grand Central.

Gravel, Debris

On 41st Street between Park and Lexington avenues, at the site of the blast, the street was ankle-deep in gravel and debris thrown from below the street by the exploding pipe. A handful of cars remained on the block. A Porsche sport utility vehicle was half turned away from the explosion, its reverse lights still on and a turn signal blinking.

Joe Petta, a spokesman for Con Ed, said there were no power failures or gas leaks associated with the blast.

Metro-North Railroad, which runs commuter train service to the suburbs north of Manhattan, was running trains normally into and out of Grand Central this morning.

Travelers can get into Grand Central from Vanderbilt Avenue, or through entrances at 47th Street and Madison Avenue or 48th Street and Park Avenue, Metro-North spokesman Dan Brucker said. There is also access via the MetLife or Helmsley buildings or through an entrance on 45th Street between Vanderbilt and Madison avenues, Brucker said.

Manhattan is home to the largest district steam system in the world, according to the Web site of the city's Economic Development Corp. While most city buildings have on-site boilers to provide heat during the winter, the Con Edison Steam Business Unit heats 1,800 buildings, serving more than 100,000 commercial and residential customers through a series of underground pipes from the Bowery in lower Manhattan to 96th Street.

The mayor is the founder and majority owner of Bloomberg News parent Bloomberg LP.

To contact the reporters on this story: Chris Dolmetsch in New York at cdolmetsch@bloomberg.net; Henry Goldman in New York at hgoldman@bloomberg.net.

Last Updated: July 19, 2007 17:24 EDT