A fire alert by a 10-year-old boy helped his septuagenarian grandparents rush out of their Dover Road flat with him after spotting the fire in their son’s room on Saturday evening.

The fire was spotted around 6.30pm after Nirban Chatterjee, a Class V student, came running to his grandmother Moushumi, complaining of an acrid smell from inside the room in their second-floor flat at 11 Dover Road.

Nirban’s mother was out buying gifts for her son’s birthday party on Sunday night and father Rathijit was elsewhere.

When Moushumi reached the adjacent room, she found that her son’s clothes were on fire. She ran down the stairs with her husband Rittik and grandson.

As thick smoke kept spiralling up, Dolly Banerjee, who was on the floor above the Chatterjees in the three-storey building all alone, didn’t know how to step out.

She managed to reach the rooftop from where firefighters rescued her and brought her down.

Dolly lost her consciousness soon after. “She regained consciousness soon, and no one was injured,” a police officer said.

It took almost an hour for three fire engines to control the fire. A team of disaster management personnel and police were present on the spot.

“We feel a short-circuit might have triggered the fire. The gas cylinder was switched off,” Rathijit said. “Thankfully, our son was not asleep and could raise the alarm at the right time.”

“We will carry out a forensic study of the room from where the fire began,” an officer of Ballygunge police station said.