Andrew Ulrich has not been to war, but he now has seen its toll on human flesh, the damage that bits of metal can wreak when packed tightly in bombs and aimed low at unprotected civilians nearby.

The physician saw it Monday, not in Baghdad or Kabul, but in the emergency room at Boston Medical Center, where he and his colleagues frantically treated injury after horrific injury to the legs and feet of 23 of the victims of the Boston Marathon bombings.

Scores treated at Boston Medical and many of the 12 other hospitals caring for victims had suffered wounds from BB-sized pellets and nails, as well as metal debris blasted into tissue and bone at close range.

“Almost all the injuries are in the lower extremities. Think of this like an IED,” Michael Zinner, chief of surgery at Brigham and Women’s Hospital, where another 31 victims were treated, said at a news conference Tuesday. At least three of those victims were hit by ball bearings and nails that appeared to be packed into the bombs, doctors said.

“We found BBs inside of kids,” said David Mooney, director of the trauma center at Boston Children’s Hospital. “We found nails that looked almost like carpet tacks, maybe a centimeter long that were sticking out of a kid’s body.”

The disproportionate number of leg injuries has convinced some medical experts that the bombs were on the ground or not high above it. The carnage from two- to three-millimeter diameter pellets and half-inch nails has convinced some that the main goal of the bombs was to injure as many people as possible.

“You can’t put into words how disturbing this is,” said trauma surgeon Tracey Dechert, who had finished a 28-hour shift at Boston Medical before the twin bombs went off, then raced back to the hospital, arriving in time to perform a double amputation on one woman. The hospital had five patients who required amputation of part of at least one leg, and “more than one” patient lost both legs, Dechert said.

At Boston Children’s Hospital, three of the nine youngsters brought in after the bombings remained hospitalized Tuesday, two in critical condition with severe leg injuries, Mooney said. Surgeons were fighting to avoid amputation, he said, because of the impact it would have on a child’s life.

“We’ll go to the mat to save a leg,” Mooney said. The third patient, a 2-year-old boy with a head injury, was in good condition and could be released later Tuesday or Wednesday, he said.

At Massachusetts General Hospital, however, doctors performed four amputations and two more limbs were at risk, said George Velmahos, chief of trauma surgery.

“Almost all of them had such severe trauma in their lower extremity that it was beyond salvation,” he said. “So I would consider them almost automatic amputees. We just completed what the bomb had done.”

Velmahos said some patients were hit by “numerous” metal pellets. “There are people who have 10, 20, 30, 40 of them in their body. Or more.”

Two brothers, Paul and J.P. Norden, who went to the marathon to cheer on a friend, each lost a leg in the bombings and were being treated at separate hospitals, according to media reports.

Ground-based explosions send metal objects packed around the charge in a concentric circle, striking feet, legs, thighs and torsos, depending on how far victims are from the bomb, said Jay A. Johannigman, a trauma surgeon and lieutenant colonel in the Air Force Reserve who has served multiple tours of duty in Iraq and Afghanistan. If the blast is strong enough and there are enough fragments, it can tear limbs off, an injury called “traumatic amputation.”

That peculiarity of this terrorist attack means that the quality of life for many survivors can, quite literally, depend on how much leg doctors can save. Physicians will work fiercely to preserve a patient’s knee because prostheses work much better when that joint is intact, said Richard Neville, chief of the division of vascular surgery at George Washington University School of Medicine. And mobility means less stress on patients’ hearts and lungs, improving their chances at long-term survival.

“It’s more than just the person’s leg,” Neville said. “You’re preserving their life, their lifestyle and their ability to function.”

Typically, 20 percent of people with severe, traumatic leg injuries face amputation, Neville said, citing figures he said were extrapolated from the results of combat. “You look at the leg and say ‘We can’t save that,’ ” usually because of artery or nerve damage, he said. A quarter to a half of those whose legs can be saved face more than one surgery. And the danger of infection is present throughout the process, he said.

One critical element in saving victims Monday, several experts said, was the use of tourniquets in the field. Joseph Blansfield, a nurse practitioner and program manager for the trauma center at Boston Medical Center, said the loss of life could have been greater if emergency medical crews had not used them to tie off the bleeding wounds of some patients as they were transported to the hospital.

“Tourniquets are a difference maker. Tourniquets can save a life,” Blansfield said. “They proved their value yesterday.” Tourniquets are part of standard care for Boston Emergency Medical Services personnel, Blansfield said. He knows because he helps train crews. Boston police, however, don’t carry them, a spokeswoman for the department said Tuesday.

Two years ago, the professional societies for surgeons and emergency physicians recommended that all ambulances carry tourniquets.

“I hope if there is a silver lining in all of this, it is that tourniquets will be more widely available across the United States,” said John B. Holcomb, chief of the Texas Trauma Institute in Houston and a retired Army colonel. “Every police officer, every firefighter and every medic should carry a tourniquet. That is the lesson from the war that the United States needs to implement.”

Some patients did arrive at the hospital without tourniquets, perhaps because the need was not apparent at the scene, he said. In those cases, hospital staff applied tourniquets, Blansfield said.

Holcomb also noted that distributing victims to numerous hospitals is a critical early decision that increases survival in mass-casualty events. “The folks in Boston are to be congratulated in doing that,” he said. “It is crucial not to overload one hospital.”

Leg injuries were not the only wounds suffered by the more than 170 people who were felled by the twin bombs but survived. Punctured eardrums, burns, heavy and rapid blood loss, broken bones and other trauma were widespread, officials said. Some victims were still in critical condition at area hospitals, and others face long and difficult rehabilitations.

“I think one thing that’s really important to remember is that, yes, this happened yesterday, but it reverberates a long time,” Peter Burke, chief of trauma surgery at Boston Medical Center, said Tuesday.

Patients face multiple operations in coming days, physical therapy and getting used to life without a limb.

“Some of them,” he said, “still could die.”

Bernstein reported from Washington. David Brown and Julie Tate contributed to this report from Washington.