A 24-year-old woman, who lived alone in a flat in Sarsuna on the city’s southern fringes, died, possibly after inhaling poisonous fumes from a fire that charred the mattress in her bedroom early on Tuesday.

Though the cause of the fire remained unknown till Tuesday evening, police and forensic officials are suspecting that a burning mosquito coil could have triggered the fire in the one-bedroom flat. As all windows were closed, the fumes got trapped inside.

Gautami Burua, who lived on the ground floor of a three-storey building at Sarkarhat Lane, was found lying unconscious at the doorsteps when the police broke open the door around 3.45am on Tuesday morning. She later died in the hospital. The police said there were no apparent burn injuries on her.

Neighbours had alerted the police early on Tuesday when thick fumes entered their home on the upper floor through an open window.

“All the windows were closed in Gautami’s apartment. The fume had come out of two openings in the kitchen and bathroom and entered our house,” said a neighbour on the first floor.

After the police came and found smoke coming out of the ground-floor apartment, they broke a glass window and then used a hammer to break open the flat’s main door.

“When the door was opened, there was only smoke and darkness. As they tried to enter, they stumbled on Gautami, who was lying lifeless on the floor in front of the door,” the building’s caretaker said.

She was breathing when the police took her to Vidyasagar State General Hospital. However, after a few hours she died in the hospital.

A neighbour said Gautami was married and her husband used to visit her often.

The body has been sent for post-mortem to be conducted on Wednesday. A forensic department team visited the spot to collect samples of the charred mattress to ascertain the origin of the fire. An officer of Sarsuna police station said they were examining if any burning mosquito coil could have caused the fire.

A senior officer said that Gautami was found near the door was proof that she had tried to open the door, possibly to let out of the fumes.

One of Gautami’s neighbours said she had lost her mother a few years ago and her grandmother very recently. Both used to stay with her as Gautami’s father works abroad, he added.

A neighbour said as Gautami lived with her grandmother, her husband used to visit them often.

In 2011, a 32-year-old senior consultant with PricewaterhouseCoopers, apparently died in his sleep in his Patuli home after inhaling carbon monoxide produced by a fire that broke out in his bedroom.

The mattress he was sleeping on along with his laptop and iPod were partially charred. It was suspected that either a short circuit in the switchboard to which the laptop was connector or a cigarette butt could have triggered the fire.