SALEM — A two-alarm fire so hot it warped the steel skeleton of a 21/2 story building was brought under control at 63 Jefferson Ave. in roughly an hour yesterday.

At the same time, a group of dogs housed on the second floor was rescued.

Workers at Allied Collision, ground-floor occupants of the building, raised the first alarm. Police officer William Riley also spotted flames around 7:49 a.m. as he was driving home from his shift. The building, which also houses Playful Paws Doggie Daycare, was described as fully involved when Riley spotted it.

"There was extensive damage," said Salem fire Lt. Peter Schaeublin, who noted that the building inspector will assess the future of the structure.

"There is significant structural damage to the front of the building where the fire started," Deputy Chief Gerry Giunta said. He described the frame of the building as "mild steel" or "red steel."

"When it's exposed to the heat, it deforms, and the steel here actually did deform," he said.

Arriving on the scene, firefighters determined that everyone was out except for several dogs on the second floor.

The building's owner and Riley made an effort to get inside and free an unknown number of dogs but were driven back by choking smoke. Riley was taken to Salem Hospital with smoke inhalation but was later determined to be all right, according to police.

Lt. Alan Dionne and firefighter Doug Sanville used a ladder to reach the dogs and rescue them from the flames.

The dogs were well-behaved and cooperative, Giunta said. "I saw a bunch of them coming out. ... All dogs love to run outside. They must have thought they were being taken out for a walk."

Putting out the fire required the entire Salem department, trucks from Marblehead and Peabody, and station coverage from Lynn and Danvers.

Firefighters faced a problem as the roof of the building was already compromised and not safe enough for crews to climb onto and vent. Thus the heat and smoke remained inside, creating a difficult environment for the men trying to control the blaze.

"It was a scary situation," Schaeublin said.

"The guys did a great job," Giunta said.

"We're still in business," Allied owner Chris Gangi said after the fire was extinguished. "Our repair facility will be in operation."

He pointed out that damage on the bottom floor seemed to be limited to the water that soaked his office.

But Giunta urged caution. "We just have to make sure it's safe," he said.

The cause of the fire remains under investigation.