And many others are being treated for nails and pellets embedded in their bodies. Virtually all suffered lower leg injuries, requiring amputations above the knee.
Trauma doctor Patrick Kim at Penn Medicine says blast injuries are extremely challenging.
Patients can suffer breathing problems, blunt injury from the blast, or flying debris. And they can also suffer skin burns.
"A victim of a blast injury might have all three types of injuries, each of which can be life-threatening," says Dr. Kim.
Both he and Dr. Steven Allen, who is director of Penn's disaster management program, say the quick action of first responders and good samaritans helped save lives.
The chief trauma surgeon at Massachusetts General agrees. Dr. George Velmahos says there were a few patients who arrived at MGH in very, very critical condition, and doctors are convinced that if they had remained at the scene for even a few more minutes, they would not be alive today.
Dr. Allen says first responders were probably expecting to treat blisters, dehydration, maybe heart attack.
But not a bombing.
He says that although you can never be fully prepared for everything, disaster drills like those hospitals, police & fire departments practice year-round in cities across the country, do help.
"The goal is to have an awareness where you can at least be in a state of mind where you can tackle these issues," says Dr. Allen.
"I think in watching the news reports and everything, once they realized what happened they shifted into a state of mind," he goes on.
"I think the response was remarkable," he adds.
Doctors at the Boston hospitals say their experience treating blast wounds serving in Iraq & Afghanistan also helped.
Still, due to the severity of injuries, many victims will likely face a long road to recovery.
Dr. Lee explained, "Survivors of this often have critical illness, long hospital stay, many surgeries and even with the best rehab many will have impairments at the end."
As of 3 p.m. today, Dr. George Velmahos reported that, "Some of them woke up today with no leg and they told me they are happy to be alive."
He added, "Some of them told me that they feel lucky and it's almost a paradox to see these patients without an extremity and saying that they feel lucky."