At 9:33 a.m. on Tuesday, the New Haven Fire Department responded to a Code Two emergency call — a possible anthrax threat. An employee of the Claims Department of Connecticut Transit had found a letter containing white powder, and three firefighters soon arrived and evacuated the building.

But the letter and its contents — corn starch — were part of a state mandated emergency response drill that takes place twice a year.

“The purpose [of the drill] is to test domestic preparedness, especially in the transportation setting,” state police officer Charles Shaw said. Other agencies involved in the drill included the New Haven Fire Department, the Federal Bureau of Investigation, the Department of Environmental Protection, the New Haven Police, and the state and city health departments. Shaw said a central purpose of the drills is to ensure smooth and efficient cooperation among the various departments.

The need for the drills is very real, said James W. Moore, deputy director of the city’s Emergency Operations Center.

During the past two years, at the height of the nation’s anthrax scare, New Haven authorities received 78 Code Two calls, several of which originated on the Yale campus. None of the calls turned out to be actual anthrax attacks. As a consequence of the volume of anthrax scares, state authorities decided that the threat of biological or chemical attacks was real enough to warrant twice-yearly drills.

Before the drill on Tuesday, members of the participating departments, as well as employees of Connecticut Transit, received a typed description of the scenario. All participants acted out their roles with seriousness. After the Claims Department employee called the authorities to report the possibility of an anthrax attack, firefighters arrived on the scene.

The firefighters said the standard plan of action for such a situation is to investigate, isolate, deny entry and quarantine — all of which they did on Tuesday. Three firefighters entered the building and evacuated all the employees, then quarantined the three workers who had come into contact with the letter and cordoned off the affected area. They proceeded to interview the employees, asking questions about where the letter had come from, who had sent it, and what it looked like.

Control of the situation was then turned over to John Cretella and Hershel Wadley, two members of the Fire Department equipped with full hazardous materials suits and gas masks. The men found the office where the letter had been left and carefully placed the letter and powder into a sealed container.

The firefighters and employees that had come into contact with the letter went through the motions of being decontaminated, although no actual chemicals were used in the drill.

“I’m 100 percent confident that any incident that happens, we’ll be prepared for it,” Fire Department Battalion Chief Kevin Delaney said. Delaney said he believed the drill had proceeded smoothly and that no weaknesses in the response strategy had surfaced.

Overall, the participants agreed with Delaney, but some employees of Connecticut Transit expressed dissatisfaction.

“I really think that if this had been real, they should have told us why we were out here,” said June Rowland, an employee of the Claims Department.

When the equipment had been packed up and the emergency response teams had left, state employees returned to their offices to resume work. But the drill was not without impact.

Division administrative officer Dean Bonanno said the drill brought home some of the realities of living in a post-Sept. 11 world.

“[The drill] made me realize that just by doing my job every day, I could be potentially handling mail that could be contaminated,” Bonanno said.