She and others said they were worried that identified individuals could be forced to evacuate to shelters that cannot accommodate people with disabilities, or that incomplete data could provide false assurances of government rescue.

For now, at least, federal officials have resolved not to identify people in “stigmatized groups” who might need help in emergencies, such as those with mental illnesses or intellectual disabilities, or those who are obese.

Dr. Karen DeSalvo, a former New Orleans health director who helped develop the Medicare pilot program and now leads the Office of the National Coordinator for Health Information Technology, said that the program protected patient privacy and that its benefits outweighed its risks. “This is the next chapter of what good data can do for good purposes,” she said. The federal government has spent more than $22 billion for the digitizing of health records.

“We are all going to have to, I’m hoping, come to some consensus with how we’re balancing privacy and security with the need to save somebody’s life,” Dr. DeSalvo said.

The idea for the program began in Tuscaloosa, Ala., after a tornado struck in April 2011. An ambulance rolled up to one of the houses left standing to take a woman to the hospital because she had run out of oxygen. “That’s kind of crazy, why can’t somebody bring her an oxygen tank?” Dr. Lurie recalled thinking after watching the scene.

She witnessed a similar phenomenon in New York after Hurricane Sandy. Patients who relied on medical equipment needed a place to plug it in before draining the batteries. Many crowded into emergency rooms, stressing the health care system. Others had no way to call for help. Eventually, emergency teams knocked on every door of darkened high-rises, because officials did not know where the people who needed assistance were.