When Delaware County firefighter Chase Frost was trapped under six feet of rubble in a blazing building, suffering burns that went down to the bone, it could easily have been the end.

Instead, he survived to take a step into the future. Make that many steps - powered by a lithium-polymer battery.

Frost, whose right leg and left arm were so damaged in the August 2007 fire that they had to be amputated, was fitted last month with a new kind of motorized prosthetic knee. He is one of more than 30 amputees worldwide to get such a device, which senses when he wants to take a step and then, using internal motors, lifts the heel and extends the leg forward.

It represents one of the latest advances in prosthetic devices, which started to enter the high-tech realm decades ago, driven largely by the interest of the military. With advanced materials, electronic sensors and now motors, they are becoming smoother, safer, and less physically taxing to wear, said Guy Fried, chief medical officer at Magee Rehabilitation Hospital.

Scientists, including some in the University of Pennsylvania's neurosurgery department, are even working to integrate prostheses directly into the patient's nervous system, so that an arm or hand could someday be operated by thought alone.

Fried said the kind of motorized fixture Frost received will become increasingly popular.

"Basically, it's the future," said Fried, who was not involved in Frost's case but has seen such devices at professional meetings. "We are slowly building the Six Million Dollar Man."

Frost, 25, is one of two local men to receive the device, the Power Knee, from an Eddystone provider called Prosthetic Innovations - one of a half-dozen practices certified to supply it nationwide.

The other local knee recipient is West Deptford resident Lou Namm, 63, a Vietnam veteran who lost parts of both legs to a booby trap.

The Power Knee, a lighter, more advanced version of a 2007 model by the same name, is made by an Icelandic company called Össur. It is not cheap, running anywhere from $75,000 to $100,000 depending on components needed by the individual patient, said Tim Rayer, one of the owners of Prosthetic Innovations. Of that total, $37,000 is the list price for certified prosthetists, an Össur spokesman said. The rest is for fitting, training, and other clinical services.

But Namm said it was worth it, reducing wear and tear on the rest of his body. He said he now can walk more than a mile with no problem, whereas he used to tire after a quarter-mile with his old hydraulic knee. His heart rate when walking with the new knee is 10 beats per minute lower.

It's also easier on his shoulders, as he barely has to push up with his arms when getting out of a chair. The motorized knee automatically straightens in response to sensors that detect the angle of his shin and the forces shifting from the heel to the toe of his artificial foot, said Rayer, the prosthetist.

Namm, a vocational counselor at the Veterans Affairs regional office in Germantown, suffered lasting damage because previously he had to stand up many times a day.

"The right shoulder has a torn rotator so bad that the doctors will not repair it," Namm said.

Frost, meanwhile, said that because of the new knee, he now needs half as much time to walk from his apartment to class at Widener University, where he is studying nursing.

And while he is still getting accustomed to using the knee on stairs, he said he has no problem lifting and transferring his own patients.

"I can't fall," Frost said. "Someone else's life depends on it."

Namm and Frost previously wore artificial knees that were already pretty high-tech, with microprocessors that regulated a hydraulic cushioning system. But they still had to contend with the loss of all that muscle, and had to compensate by kicking their leg forward with every step.

Now, the Power Knee does the work for them. Though, at six pounds, it weighs a pound or two more than their old hydraulic knees, they said it feels lighter because of the work done by the motors.

Frost, who suffered his injuries when the ceiling of a burning townhouse collapsed on him in Parkside, is in the process of seeking coverage for his knee from the state worker's compensation program.

Namm said the cost of his Power Knee is being covered by the VA, and that he was told he was the first veteran to get one. He said it was approved because tests showed it was better for his heart and overall health.

Alas, Vietnam amputees such as Namm now have plenty of company from more recent engagements. Through Jan. 18, there had been 1,549 amputations as the result of injuries sustained in the conflicts in Iraq and Afghanistan, according to Defense Department spokeswoman Cynthia Smith. A few have received Power Knees at Walter Reed Army Medical Center.

Most amputations, however, are performed on people with vascular disease or diabetes, according to the Amputee Coalition, a Tennessee-based nonprofit.

Rayer, of Prosthetic Innovations, first became interested in the field when playing basketball at Pennsylvania State University's Brandywine campus, where a teammate lost a leg to cancer. Rayer was fascinated by his teammate's artificial leg and eventually went to school to become a prosthetist.

He also got his brother, Mike, interested in entering the field, and the two now own Prosthetic Innovations with partner Chris Dalmass.

The practice is located in an old hangar that once was used to test Baldwin steam engines. A harness hangs from a steel beam high overhead so that patients can be supported while they get used to their new devices on a treadmill.

Mike Rayer, who is also a mechanical engineer, said they were among the few places certified to sell the new Power Knee so far because they had helped with early testing, and because they were known for a willingness to work with cutting-edge technology.

"We kind of developed a reputation of being people that like to tinker," he said.

He was drawn to the profession because of the immediate impact on patients.

"No delayed rewards. You actually get something right away for all the work you put into it."

Now one of those patients - Frost - is moving well enough to help his own patients. Already attending nursing school part time before his accident, Frost is now pursuing his studies full time.

Frost said his patients do not even realize he has an artificial leg, because it is covered by hospital scrubs, though they do notice his non-motorized prosthetic arm.

"They see the arm and you can tell the way they look, they question it," Frost said. "Once they see I can perform, they don't have a problem."