Office workers and residents reacted warily yesterday as city officials declared the air free of toxins a day after a steam pipe explosion in Midtown Manhattan.

With workers in yellow Hazmat suits crisscrossing the area, some New Yorkers said they still felt shaken after the giant blast near Grand Central Terminal, which killed one person, identified by authorities as Lois Baumerich, 57, of Hawthorne, N.J., and injured 45 more.

“I was two blocks away from ground zero when that happened, and they assured us the air quality was fine, and that turned out to be false,” a medical malpractice lawyer who works in the area, Dominic Boone, said after lifting a surgical mask he donned to go to work near the so-called frozen zone. “It’s best to be prudent.”

Others were less fearful, including a doorman at the nearby Murray Hill Suites Hotel, Pawel Kosior, 25, who said he and other hotel workers had sore throats yesterday morning.

“My throat felt like there was a heavy dust in there,” he said. “I was a little bit worried. Not now.” Officials yesterday sought to reassure New Yorkers that buildings near the explosion site were structurally sound and that any asbestos released as a result of the blast was contained in mud and debris and did not escape into the air.

“Every single test we did of the air showed there is no asbestos,” Mayor Bloomberg said. Only trace amounts were found in most of the samples of debris, he added.

By yesterday, subway service had resumed and officials said that over the next week they would be shrinking the frozen zone, which as of yesterday was bordered by 40th and 43rd streets and Vanderbilt and Third avenues.

Many businesses that occupy the tall buildings concentrated in the zone were forced to close yesterday, although residents in the area were not evacuated.

The chairman of Consolidated Edison, the power company that maintains the steam system, Kevin Burke, said the utility would be responsible for repairing the truck-size hole in the middle of Lexington Avenue created by the explosion, but he did not give a time frame for the operation. He said the investigation into the cause of the blast was ongoing.

Yesterday, local politicians called for an investigation of the utility, three weeks after a brief electrical power outage swept across the Upper East Side and the Bronx.

“Their history of neglect has robbed them of the benefit of the doubt,” a Queens City Council member, Eric Gioia, who has been vocal in criticizing the company following a nine-day power outage in Astoria last summer, said. Mr. Gioia’s wife, Lisa Hernandez Gioia, was forced to flee her office, a block from 41st Street and Lexington Avenue, after the explosion Wednesday evening, he said.

“The question is whether this was unavoidable because of our aging infrastructure, or if this was another example of Con Ed’s negligence,” he added.

By yesterday afternoon, a City Council hearing had been scheduled to look into the utility’s actions on the day of explosion, including a probe into the inspection team that checked the pipe hours before it burst.

Exploding steam pipes that spew geysers of asbestos into the air were a more frequent occurrence in New York City before a deadly explosion near Gramercy Park in 1989 killed three, a spokesman for the utility, Chris Olert, said.

After that explosion, a federal monitor was put in place to oversee the utility’s operations.

But Gerald Sauer, the father-in-law of Ellen Sauer, who died in the 1989 explosion, said he wasn’t surprised at Wednesday’s repeat of that disaster.

“It was just a matter of time until it happened again,” he said from his home in Florida, where he said he and his family moved because they “just didn’t want to be in New York” anymore after the tragedy.