Half a million times a year — about once every minute — ambulances carrying sick patients are turned away from full emergency rooms and sent to others farther away.

It's a sobering symptom of how the nation's emergency-care system is overcrowded and overwhelmed, "at its breaking point," concludes an investigation by the Institute of Medicine.

"The safety net ... has large holes," co-author Dr. A. Brent Eastman, chief medical officer at ScrippsHealth in San Diego, said Wednesday. "You may not be caught and saved when your life depends on it."

How many people die as a result? The two-year probe couldn't come up with an answer; there's little tracking of how emergency patients fare after that frantic 911 call or race to the hospital. But there are troubling clues. For example, in some cities, emergency workers save half of the victims of cardiac arrest — but in other places, they save merely 5 percent.

This nationwide crisis comes from just day-to-day emergencies. Emergency rooms are far from ready to handle the mass casualties that a bird flu epidemic or terrorist strike would bring, the institute said Wednesday in a three-volume report.

"If you can barely get through the night's 911 calls, how on earth can you handle a disaster?" asked report co-author Dr. Arthur Kellerman, Emory University's emergency medicine chief.

Even a school bus crash would qualify as a disaster for most hospitals: Although children make up more than a quarter of all ER visits, only 6 percent of emergency departments have all the supplies needed — such as child-sized equipment — to treat pediatric emergencies, and few have doctors trained in children's care either, the IOM panel found.

That ERs are overburdened isn't new. But the probe by the IOM, an independent scientific group that advises the government, provides an unprecedented look at the problem's scope — and recommends urgent steps for health organizations and local and federal officials to start fixing it.

At the root of the crisis: Demand for emergency care is surging, even as the capacity for hospitals, ambulance services and other emergency workers to provide it is dropping.

There were almost 114 million emergency room visits in 2003, up from 90 million a decade earlier. Only about half were true medical emergencies. When the poor and uninsured can't get health care anywhere else, they come to emergency rooms, which must treat them regardless of ability to pay.

"It is the only medical care to which Americans have a legal right," noted Kellerman, adding that what constitutes an emergency is different to a doctor than to a desperate patient. Last week, he treated a woman who wound up in the ER after running out of some crucial medication and being turned away by four different clinics.

Yet lack of reimbursement for ER care is one reason some emergency departments go out of business. During the past decade, the total number of U.S. hospitals decreased by 703, and the number of ERs by 425. And the total number of hospital beds dropped nationwide by 198,000, due also to the trend toward cheaper outpatient care.

That in turn means long waits in crowded ERs for hospital rooms to open up. Once stabilized, patients can lie on gurneys in the ER hallway not just for hours but for two days. The new report found that on a typical Monday evening, three-quarters of hospitals reported at least two patients boarded in the halls.

Even getting to the ER is a gamble, the report found, because the EMS system — emergency medical services that include ambulances, and paramedics — is so fragmented. How well-trained and prompt local paramedics are varies greatly; there are no nationwide standards. Many ambulance services can't even effectively communicate with hospitals or other first responders because they use radio equipment from the 1970s.

Topping the report's recommendation list is a call for states and hospitals to set up regionally coordinated emergency systems that manage patient flow to avoid overcrowding much like airports direct flight traffic. They would direct ambulances not necessarily to the nearest ER but to the one best equipped to treat each patient's condition.

Other recommendations:

— Congress should establish a pool of $50 million to reimburse hospitals for unpaid emergency care provided to the poor and uninsured.

— Congress should ensure that more of the nation's disaster-preparedness funding goes to the hospitals and emergency workers who will provide that care. First-responders, such as ambulance and paramedic services, have received 4 percent of that money to date. And typical government grants to hospitals for bioterrorism preparation are $5,000 to $10,000 — not enough to equip one critical-care room.

— Hospitals should stop diverting ambulances and boarding patients in the hallways.

"I didn't say work on it. We said they must end it. This is simply unacceptable," Kellerman said.

The American College of Emergency Physicians called the report groundbreaking but said Congress must heed recommendations to fund the necessary improvements.