The threat from Allied bombing raids is still far from over in Germany, even though the war ended 52 years ago.

The risk comes from unexploded bombs lying just below the ground where they fell.Nearly every week, a neighborhood in or around Berlin receives a phone call from the police telling inhabitants to evacuate their homes until a World War II bomb is defused and they are out of danger.

"Here we are, seven to eight years before retirement, but the work could last at least another generation," said Norbert Funke, the greying director of Berlin Aerial Photography Analysis, which examines U.S. and British wartime photographs for signs of unexploded bombs beneath the city.

Funke and his four colleagues spend six hours a day squinting over the black-and-white stereoscopic (three-dimensional) pictures, looking for shallow craters where bombs during the 1940s may have landed but not exploded.

Once they find the small crescent path of an undetonated bomb on one of their 8,000 photos, which British and U.S. air forces took to determine a raid's success, they send surveying teams with metal detectors to investigate on site.

In 1983, a 1,100-pound bomb went off in front of a school in a central Berlin district, fortunately during the summer recess. Later that year, the city of West Berlin opened Funke's office and entrusted his team with preventing a repeat.

Despite 14 years of work, the team - which now covers the whole of the Berlin area - cannot say a district is completely free of danger. Explosives continually surface under schools, behind the Brandenburg Gate, in the future federal government quarter.

"If you worked eight hours a day at this, a normal work day for most people, you wouldn't make it," Funke said, referring to of the level of concentration required. "The biggest worry is that you'll overlook something."

In September 1994, Funke's nightmare came true. Three construction workers were killed and several injured when an excavator tripped the fuse of a U.S. bomb which had been covered by only a few feet of dirt.

Officials from the Berlin prosecutors' office questioned Funke's staff shortly after the blast. Although they were cleared of any negligence, Funke said the incident still haunted him.

"You ask yourself who should take the blame," he said. "That is always an issue for us."

Since that explosion, construction teams are required to consult the department's aerial photograph analyses before beginning work.

As the capital of Nazi Germany, more bombs fell on Berlin during 1943 and 1944 than any other German city. Up to 50,000 died in the raids.

"Every day, Allied planes swooped by once or twice. In a big attack, you saw 1,200 fighter planes. The skies were black," Funke said.