A team of investigators hunted for evidence Tuesday in the cause of a Back Bay fire that took the lives of two Boston firefighters and injured more than 13 last week.
Lieutenant William McCarthy of the Fire Department’s investigation unit said the investigators were at 298 Beacon St. to assess the damage as part of their ongoing probe.
The cause of the fire has not been determined, authorities said.
“It is standard operating procedure,’’ McCarthy said of Tuesday activity in the charred four-story building. “We rule out whether it was mechanical, electrical, or chemical’’ causes for the fire.
The fire, which began in the basement, quickly gained intensity on a windy afternoon and went to nine alarms. Lieutenant Edward J. Walsh Jr. and Firefighter Michael R. Kennedy, who had hauled in a hose to fight the flames, were trapped inside and could not escape.
On Tuesday, a lane of traffic in front of 298 Beacon St. was cordoned off with yellow tape.
Investigators spent some of the day using a 3-D laser scanner that takes measurements and can create realistic 3-D images of buildings, spaces, and large objects, according to the device’s manufacturer.
Investigators were also seen going in and out of the building’s front door and up and down exterior stairs leading to the basement.
A bright green evidence marker was placed in the road directly in front of the building’s entrance and a fire hose sat undisturbed on the stairs.
A prosecutor with training in fire investigations has been assigned to the case, said Jake Wark, a spokesman for Suffolk District Attorney Daniel F. Conley.
Wark described the assignment of the prosecutor as a routine step in death investigations.
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