BERLIN (AP) – Authorities are investigating yet another fire in Berlin, the latest in a string of a dozen major fires this year.

A three-alarm fire destroyed a vacant home early Saturday, immediately prompting suspicion.

“When the building is vacant and has no electricity, and knowing the history of what’s been happening, it’s a red flag right away,” said fire Capt. Rob Jewett.

What’s been happening is a dozen major fires since January, including one a week ago that left 12 residents of an apartment building homeless. Some have been listed as suspicious and at least two are classified as arson.

No one was hurt in Saturday’s fire and the cause is listed as undetermined. State and local fire investigators are on the case. The fire was reported just after 4 a.m., on 3rd Street. It was under control within about 45 minutes.

A week earlier, fire destroyed a three-story apartment building. Investigators said it probably was not suspicious. The cause of a fire that hit two apartment buildings in the same neighborhood in June is undetermined, but officials have said two other fires on opposite sides of the city earlier in June were arson and a number of others this year are suspicious.

In January, three people were killed in a fire that gutted two apartment buildings, and two more buildings were heavily damaged in another fire in February. That prompted state fire inspectors to examine a number of buildings in Berlin. Jewett said the major fires, as well as many others that haven’t made the news, are taking their toll on the department.

“We’re a very tired bunch,” he said.

“The guys are on edge,” he said. “You go to work and say ‘Where is the fire going to be tonight?”‘ The department typically has four firefighters on duty and calls off-duty firefighters when they need extra help. But Jewett said the department is understaffed, as illustrated when Saturday’s fire went to three alarms and brought only a total of a dozen firefighters to the scene.

Jewett said he and his colleagues are keeping their fingers crossed. “God help us that one of us doesn’t get seriously injured or killed,” he said. “We’ve had a lot of close calls.”