Tracking personnel inside buildings: a tough problem to solve.

LOS ANGELES -- In the defense community it's called "blue force tracking," or the ability to know where your personnel are at all times.

First responders call it "accountability," and it was one of the major needs identified in the wake of 9/11.

Fifteen alarms sounded and more than 750 firefighters responded when the hijacked planes struck the towers, said Chief Robert Ingram, branch chief for weapons of mass destruction at the New York City Fire Department and chairman of the InterAgency Board for Equipment Standardization. Many of those firefighters lost their lives after they entered the buildings.

"How do you track that manually? You can't. And that is why other disciplines and agencies lose people," he said.

The InterAgency Board, a working group of first responders that identifies and approves technologies for use by police, fire and ambulance services, has listed the development of a 3-D tracking system as one of its top research priorities, he said. Commanders want icons on a screen showing them where all their personnel are, especially while they're inside buildings.

For New York, it's not as simple as sticking a Global Positioning System transmitter on a firefighter. As soon as they enter the subway or one of the city's 1,700 high rises, that signal weakens, or is lost altogether.

More than six years after 9/11, the fire department is still using a whiteboard and magic markers to keep track of personnel, he said. "It does not matter if it's fire, police or emergency medical services, everyone can use an accountability system like this," Ingram said.

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The Homeland Security Advanced Research Projects Agency planned to test a prototype system in February that will let those manning command and control vehicles track firefighters when they enter a building.

Jalal Mapar, HSARPA program manager, said the first responder 3-D locator relies on a "cocktail solution." Five different systems will collect data to give a "best estimate" of locations. The goal is to "allow emergency managers ... to rapidly and effectively deploy and redeploy their forces or understand and respond to the consequences of potential threats to their forces."

The first of the five sensors is the most unreliable when entering a building. GPS signals are weak, and quickly fade when steel and concrete get in the way.

After that, the four other systems take over.

An accelerometer, or inertial navigation system commonly found on missile guidance sensors, measures where the subject is going and makes estimates of location in three dimensions.

Those on missiles are prohibitively expensive, but the rudimentary sensor on the prototype costs only a few dollars, he said. Ultrawideband for radio ranging sends a signal to the subject and measures how long it takes to get it back. A pedometer measures the footsteps, and a barometric altimeter measures air pressure to calculate how far up the subject has moved inside a high rise.

"If you go in a building or you go underground where you don't get a signal, these other systems compensate," Mapar said. "If I get four or five data points, and one drops out, I can get three I can deal with."

The system includes a distress button, and also alerts commanders when the subject has stopped moving.

The field tests will have to show at least two hours of operation, and that the locator can withstand the rigors of being inside a burning building. It must be resistant to electrical charges, gasses, hard impacts and water. Most importantly, it must be accurate to within three meters, but preferably one, he added.

About 10 units will be sent to the New York City Fire Department for field tests, he added.