With its airy lobby and sunlit corridors, the Department of Homeland Security lab at Fort Detrick looks at first more like a modern office building than a place where some of the world's deadliest substances are handled.

But the mission becomes clearer as those corridors lead to clusters of rooms, some with submarine-style air locks and foot-thick concrete walls, where air flows are measured and displayed on monitors throughout the building.

And instead of art, images of bacteria hang on the wall.

Three years after it opened on this Army base in Frederick, the National Biodefense Analysis and Countermeasures Center has become an integral part of the effort to fight bioterrorism. Though officials at the lab do not discuss individual cases, the FBI disclosed recently that the facility's scientists were responsible for testing the letter sent to the White House in April that contained the deadly compound ricin.

"We're on call 24 hours a day," said lab director Pat Fitch. "And when we're called on, we're ready."

The DHS lab is charged with studying the risks posed by biological threats and performing bioforensic analysis when those dangerous agents are used in a crime. By studying the material, scientists often can discern how and where it was made.

And that can lead to clues about who made it.

The $143 million facility opened in 2010 and is managed by Battelle National Biodefense Institute, a subsidiary of Ohio-based contractor Battelle Memorial Institute.

Homeland Security is one of at least seven federal agencies performing biological research at Detrick. The U.S. Army Medical Research Institute of Infectious Diseases will soon move into a massive new building next to the DHS lab. The National Institutes of Health and the Navy also perform high-level research on the base.

Fitch said the unique concentration of labs fosters cross-agency collaboration. Local officials hope the investment by the federal government will spur private economic development similar to what has taken shape around federal cybersecurity at Fort Meade.

The DHS facility employs 150 people and has an annual operating budget of about $50 million.

"The fact that these labs are here means that a lot of other organizations … are either supplying those labs with services or products," said Richard Griffin, director of economic development for the city of Frederick. "Fort Detrick has been doing bioscience work since the '40s and '50s, and so Frederick has a very deep workforce in biotechnology."

Ricin-tainted letters addressed to President Barack Obama, Republican Sen. Roger Wicker of Mississippi, and a Mississippi judge were intercepted by mail-processing facilities in mid-April. An FBI affidavit filed April 26 as part of that investigation noted that the DHS lab at Fort Detrick had tested all three letters and confirmed the presence of ricin.

Fitch declined to discuss the case.

A 41-year-old Mississippi man, James Everett Dutschke, has been indicted in the case. Dutschke pleaded not guilty last week.

New letters containing ricin were mailed to the White House and New York Mayor Michael Bloomberg in late May. FBI agents have twice searched a home in Texas in that case, but no charges have been filed.

Ricin, which is derived from castor beans, is highly toxic; however, it is not easily processed into an airborne weapon. Experts have speculated that the ricin letters would be dangerous only if recipients consumed the powder.

The DHS lab houses laboratories that handle material classified at three threat levels. Anthrax, for example, is generally considered a "biosafety level 3" substance. The most dangerous category, BSL-4, is reserved for fatal viruses and substances that are susceptible to becoming airborne and for which there are no vaccines.

Hemorrhagic fevers, such as the Ebola virus, are handled in the highest-level labs.

Scientists in those labs wear full-body pressure suits and are monitored remotely as they work.