Residents in the Warwick Village neighborhood of Alexandria said that one neighbor was sickened and others were driven from their homes for hours when styrene vapor, a byproduct of ongoing repairs to city sewer lines, seeped into their houses.

City officials said yesterday that the toxic fumes might have affected more residents than they initially disclosed. They were still examining fire department records to determine how many residents called asking for aid because of the fumes.

Officials had said last week that the only problems were experienced by two Alexandria residents from Warwick Village and Beverley Hills who had sought medical treatment after exposure to styrene vapor from the sewer repairs. Those repairs began in late March.

But city officials did not disclose that, on April 28, several residents in Warwick Village were afraid to return to their homes for hours, or even overnight, because of the overwhelming smell. Styrene vapor escapes as resin being applied as a liner to leaky sewer pipes hardens.

On that evening two weeks ago, the Alexandria Fire Department hazardous materials team was called to the scene and found a blue hose, apparently left behind by the contractor. The hose was emitting styrene vapor with a concentration of 500 parts per million, according to an incident report.

Environmental Protection Agency guidelines state that exposure above 50 ppm for more than one hour could cause serious illness. Effects from the fumes include nausea, dizziness, fatigue and eye irritation.

Rich Baier, the city's public works chief, said tests taken in the sewers and in homes have determined that concentrations of styrene vapor are within acceptable levels. Baier said he did not know about the blue hose.

The city is taking steps to prevent further problems, Baier said. It has distributed new literature door-to-door, advising residents to fill dry pipe traps with water to prevent fumes from entering through pipes. Workers also are ventilating manholes and flushing sewer lines with water.

The city recently launched a six-year, $18 million upgrade of its aging sewer system, hoping to stem leaks that often cause basement flooding.

In March, contractors from Missouri-based Insituform Technologies Inc. began rehabilitating almost 16 miles of sewer lines. The company uses a resin compound to line existing pipes instead of the more expensive option of digging up and replacing old pipes.

Greg Laszczynski, Insituform's regional operations manager, said that the company has been doing work for Fairfax County, Arlington County, the city of Falls Church, Baltimore and Richmond and the Washington Suburban Sanitary Commission, which serves Montgomery and Prince George's counties, since 1978.

He said that over the years, he has heard reports of about 10 residents having adverse reactions to styrene fumes.

"On rare occasions, we've had people overreact, as we've had in this situation, and go to the hospital as a result of smelling the styrene . . . which can cause your eyes to burn and your nose to run, much like smelling ammonia," Laszczynski said. He said he does not believe there was anything structurally different about Alexandria's sewer system that would have caused more problems than elsewhere.

Maurice MacDonald, a D.C. police officer, said he was returning to his Warwick Village townhouse about 4 p.m. April 28 when he noticed the smell.

"It smelled like glue or paint thinner," MacDonald said. "I started to feel nauseated, light-headed, short of breath and my eyes were burning. . . . My eyes felt like they were actually on fire."

MacDonald's wife took him to an urgent-care center, where he was diagnosed with an inhalation injury. He missed five days of work and said he is considering suing the city.

Another neighbor, Harry Pastuszek, a policy officer at the World Bank, said the styrene smell was so strong that he was afraid to return to his home with his 19-month-old son until after 8:30 p.m. Pastuszek vomited repeatedly the next day. At the time, Pastuszek said, he thought he had food poisoning.

"One person ill is one too many," said Alexandria spokeswoman Barbara Gordon, adding that the city was doing everything it could to ensure the safety of its residents while the work is underway. "The city is trying to improve the quality of life for people by improving the sewer system."

Maurice MacDonald, 32, and Pamela Underhill, 42, describe being forced from their homes in Warwick Village on April 28 because of styrene fumes. MacDonald, a D.C. police officer, was diagnosed with an inhalation injury.