The Fire Department changes stem from a 2009 ruling by a federal judge, Nicholas G. Garaufis of Federal District Court in Brooklyn, who found that the city used exams that discriminated against black and Hispanic applicants. The judge ruled that the exams given in 1999 and 2002 had disparate impact, a legal term applied to employment practices that adversely affect specific minorities. In this case, the white applicants’ performing significantly better than minority applicants was evidence of bias.

Judge Garaufis ordered the city to create a new entrance exam and appointed an independent monitor to oversee changes in recruiting, testing and hiring. Most controversially, Judge Garaufis required the department to give a second chance to some minority recruits, including some who had failed exams, in 1999 or 2002, that were found to be biased. For those recruits, the department was required to waive the maximum age of 29 for taking the entry exam and to provide back pay and salaries commensurate with the time they would have put in had they been hired earlier.

The current class includes 76 of these recruits, known as priority hires, who will enter the firehouses for the first time after graduation on Dec. 5. Many of them will be older than colleagues, and some will have higher pay. Paul Mannix, a deputy chief and a fire commander in the Bronx who leads a group opposing the reforms, said that while he was pleased to see the new recruits held to a rigorous standard at the academy, the inclusion of priority hires was unfair and was harming morale.

“There’s a corrosive and toxic atmosphere that’s being created in the Fire Department at this time because of the preferential treatment that is going on,” he said.

To dispel what the department describes as misinformation surrounding the new class, officials allowed a reporter to interview and observe recruits over several weeks at the Rock, the Fire Department’s sprawling training center on Randalls Island.

Those interviewed included military veterans, former emergency medical workers and other city workers. Some traced their passion for the job to childhood. Others were inspired by the Sept. 11 terrorist attack, which killed 343 New York City firefighters. Most said they were unaware of the litigation until the application forms arrived. But they said were prepared to be thrust into an important experiment.

Dwayne Hill, 34, is a former combat engineer in the Army. He passed the 2002 entrance exam, but was called to active duty before he could reach the academy. After a year in Iraq clearing mines, Mr. Hill, who is African-American, returned to find he had missed the opportunity to join the department.