A third fire in less than two years broke out about 5 p.m. at the abandoned Pennington Place Apartments in Lexington on Thursday.
Assistant Fire Chief David Ades said firefighters approached the situation as if people were in the building at 245 Codell Drive because of the prevalence of squatters and children who frequent it.
No one was injured.
Ades said the cause is unknown and the amount of damage will make it difficult to determine. There is no electricity in the buildings.
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The fire, which was extinguished within 20 minutes, was contained to one unit although it went through the roof of that building.
Vanessa Gibens, who has lived in the Codell neighborhood since the early '90s, said she often sees people going in and out of the abandoned complex. She said the building is a popular place for teens and whole families often live illegally in the apartments.
Because abandoned buildings are always a risk for fires, Ades said, it is up to the city to look into possibilities to resolve the dangerous situation and look into options such as demolition.
Ades said the fire department would keep a presence outside the building overnight.