Carol Oldfield mistakenly filled a pan with the lubricating oil instead of cooking oil at her home in Ripley, a town in Derbyshire, U.K. on March 6 this year, the Derby Telegraph reported.

The 74-year-old turned her cooker on in the kitchen before going into the living room and falling asleep for a couple of hours, according to the newspaper.

Derbyshire Coroner’s Court heard how Oldfield woke up from her nap to find her home had filled up with white smoke.

A spokesperson for Derbyshire Fire and Rescue Service told Newsweek that firefighters responded to Oldfield’s home at around 7 p.m. on March 6.

“Crews rescued Carol Oldfield from the front bedroom of the property and walked her outside, handing into the care of paramedics from East Midlands Ambulance Service,” the spokesperson said. “The fire was in the kitchen of the property.”

Assistant coroner Emma Serrano told the hearing, which was held remotely, that Oldfield had told firefighters that she wasn’t able to find a way out of her home because of the smoke.

Firefighters told her to wait upstairs until they could ventilate the house and escort her out.

The inquest heard that initially, it appeared that Oldfield had emerged from the ordeal largely unscathed.

But Dr. Marco Giovannelli, a consultant who works at Royal Derby Hospital, wrote in a report that Oldfield’s condition deteriorated over the following days.

She started coughing and complained of having a hoarse throat, the doctor wrote. An examination of her brain showed that she had early signs of dementia.

On March 16, Oldfield was moved to end-of-life care and she died two days later.

Summing up the case, Serrano said the three-in-one oil Oldfield had used was different to cooking oil.

“She turned on the hob and went into the front room and fell asleep. The room filled with white smoke, which she inhaled,” she said, according to the Derby Telegraph.

“She woke up and called the fire service who managed to get her out of the address but sadly the damage had already happened She did not recover and sadly passed away.”

Oldfield’s cause of death was listed as pneumonia and smoke inhalation. Serrano ruled that Oldfield’s death was due to misadventure.

An obituary published in local newspaper the Ripley & Heanor News said Oldfield “passed away peacefully” on March 18 and that a private family funeral service had been held on April 17.

The obituary added that she would be “greatly missed” by her surviving family members and friends.

This article has been updated with comments from Derbyshire Fire and Rescue Service.