CARMEL MOUNTAIN RANCH -- Within a huge building at the U.S. Postal Service center in Carmel Mountain Ranch, outgoing letters are now routinely checked for anthrax.

The new detection system was explained Wednesday to emergency response representatives and the media at the Margaret Sellers Processing and Distribution Center, 1251 Rancho Carmel Drive.

Christina Grimmett, a 20-year postal employee, ignored the group as she sorted batches of mail on the center's 400,000-square-foot work floor.

"I think (the system's) good," said Grimmett, speaking above the noisy machinery. "It will be an advance warning if there's anything in the building."

The system was designed exclusively for the Postal Service after five people, including two postal employees, died when letters containing anthrax were mailed to officials and the media in October 2001.

The North County postal center is one of the largest in the nation, processing about 6 million pieces of mail daily. It is the only mail center that postmarks and cancels mail in San Diego County.

About 1 million to 2 million pieces daily are letters, said Mike Cannone, Postal Service spokesman.

San Diego is the 66th mail center in the nation out of 100 that will get the new biohazard detection system this year under a $175 million contract with Northrop Grumman.

None of the systems had reported positive anthrax tests as of Wednesday afternoon.

By the end of 2005, 270 postal facilities across the country will have the system, officials said.

After two years of testing to be sure it worked and wouldn't interfere with mail flow, the new system uses sophisticated DNA matching to detect anthrax in outgoing letters.

Another process is used to check suspicious packages, officials said.

The biohazard detection equipment, housed in a cabinet about as big as a medium-sized copier, collects air samples as mail moves through the canceling machine.

Between 3 and 9 p.m. daily, the system absorbs airborne particles into a liquid sample. The sample is injected into a cartridge, then automatically tested for a DNA match similar to anthrax.

In addition to the biohazard detection system, officials said, mail is also photographed. A contaminated letter would probably be found within 90 minutes to two hours, they said.

"Chances are that (in that amount of time), mail is still going to be in the building," said Cannone. "This building would be shut down."

Battalion Chief Dave Williams, special operations hazardous materials program manager for San Diego Fire Rescue, said the Poway Fire Department and other agencies will be briefed on an emergency anthrax response in the event of a positive test.

"We treat it no different than a 911 response," Williams said.

About 1,900 employees at the center have already drilled on what to do if the alarm -- a flashing red light and a horn -- goes off, officials said.

At that point, said Cannone, the Postal Inspection Service and local emergency authorities would take over. There is a process for notifying officials, evacuation and decontamination.

"The whole building would be a crime scene," said Richard Whaley, emergency management specialist for the Postal Service.

Contact staff writer Jo Moreland at (760) 740-3524 or jmoreland@nctimes.com.