The city’s firefighters are outgrowing their name this summer as the fire academy prepares to teach new recruits skills ranging from responding to improvised explosive devices to rescuing children from abusive homes.

“From the time I came on the job 30 years ago, the threats they are faced with day to day have increased,” the head of training for the fire department, Assistant Chief Thomas Galvin, said. “That’s why we’re increasing the WMD training.”

The expanded training comes as the fire department initiates a major shift in its entrance requirements this August, including nearly doubling the time probationary firefighters once spent in the academy, to 23 weeks from 13. The time they spend studying weapons of mass destruction, explosive devices, and other hazardous materials will increase to 40 hours from 24.

Fire department officials say future graduates will come out more prepared to respond to a new landscape of threats as terrorist plots have increasingly resembled tactics used in Iraq, including a recent plan to blow up a fuel pipeline at John F. Kennedy airport and plots discovered in Britain over the weekend involving car bombs.

The extra training in improvised explosive devices will include an examination of models based on devices that have been used in war zones in the past.

But the main focus of the extra weeks of training will be on architecture and structural engineering.

Mr. Galvin explained that most new buildings are now made of relatively lightweight materials that, while structurally sound, often burn faster and hotter than the materials in older buildings. These days, an average building fire burns almost twice as hot — at about 1,500 degrees — as a fire 50 years ago.

Firefighter recruits will also spend more time in the academy’s flash-fire and subway simulators, where they practice responding to victims of subway accidents and evacuating riders from tunnels.

In addition, at the request of Mayor Bloomberg, they will be trained to look for other sorts of victims in the wake of several high-profile child abuse cases, including the death of 7-year-old Nixzmary Brown last year. A new six-hour module on how to recognize domestic abuse, Mr. Galvin said, can help “prevent a tragedy from happening.”

But as the changes are implemented next month, some current and former firefighters are warning that the increased rigor of the academy has been accompanied by easier academic and physical requirements that they say could lead to a less-qualified class of recruits, even as the demands of the job increase.

To be eligible for the fire academy, applicants must have an honorable discharge from the military, six months of work experience, or 15 college credits, reduced last year from 30 college credits. And the department is introducing a new physical exam starting next year based on a national standard.

“You’re going to see a change in the level of firefighting,” a retired fire captain who now trains firefighter hopefuls, Michael Stefano, said. “You’re going to see a huge death toll in the city.”

Plans to introduce the new test, the Candidate Physical Abilities Test, were announced in the fall. It includes eight events that firefighters must complete in 10 minutes and 20 seconds, including raising a ladder, crawling through a tunnel, and dragging a dummy — a time limit that Mr. Galvin said the department is hoping to reduce in the future to make the test harder.

The change that has drawn the most criticism is the physical test’s new pass-fail grading system. Before, applicants were ranked according to their performance on both the physical and written tests.

“It doesn’t give the firefighters who are in excellent shape an advantage,” a 42-year veteran of the FDNY and a deputy chief, Vincent Dunn, said.

A captain at a Midtown firehouse, Richard Patterson, said speed should be the overriding factor in deciding who should become a firefighter.

“Speed makes the difference,” he said. “That’s why fire-trucks have sirens, so they can get through the streets. That’s why we have a pole in the firehouse. Speed is the whole thing we’re up against.”

The firefighter union, the Uniformed Firefighters Association, and the Vulcan Society, an organization of black firefighters, have also said they were concerned about the switch to the new test.

“There’s nothing more important than physical agility to a firefighter,” the vice president of the union, James Slevin, said. “The concern is that if you’re lowering the standards in the future, we’re going to have problems.”

Advocates for women firefighters have hailed the introduction of the Candidate Physical Abilities Test as a victory, however, saying it will “level the playing field” for female candidates.

“There really isn’t any data to show that somebody who does better,” on the physical test, “is going to be a better firefighter,” the executive director of the national group, Women in the Fire Service Inc., Terese Floren, said.

Mr. Galvin also rejected the criticism, saying that the longer training will ensure that new firefighters are just as prepared for the job as their predecessors.

Instead of waiting up to four years after taking the physical entrance exam to enter the academy, he added, new recruits will now be brought into the academy within six months of passing the physical exam.

“At the end of the day, we’re going to come out with a firefighter who is in better shape, who is more knowledgeable, and who is in a better position to protect the city,” he said.