A fire which engulfed a home in Parry Avenue in the early hours of June 9 last year could have been caused by drone batteries left to charge overnight, a coroner's court heard yesterday.

Calling it a "tragic misadventure", State Coroner Marvin Bay said that the fire was "accidental in nature" and "electrical in origin". He found no basis to suspect foul play.

In just two hours, businessman Tang Hui Jen's home off Yio Chu Kang Road, where his four-generation family lived, was reduced to a charred state.

The blaze claimed the lives of his 64-year-old wife Angeline Tan and his Australian business partner of 30 years, Mr Ian Johnson, 74, who was a guest at their home.

Six people, including two firefighters, sustained minor smoke inhalation and heat-related injuries.

The fire started at about 3am in the living room of the two-storey semi-detached house, where three drone lithium polymer batteries had been left to charge on the carpeted floor beside the sofa.

The batteries were for a multirotor service drone, the G4 Surveying Robot, that Mr Tang and Mr Johnson intended to import and distribute locally.

Other electrical items, such as an electrical reclining sofa set and massage chair, were also not completely turned off.

There were also power extension sockets near the sofa and running under the living room carpet, which were used to charge various household electrical items.

Domestic helper Noemi Lozano Corpuz was asleep in a room on the first floor when she was awakened by the smell of smoke. Upon seeing the sofa area on fire, Ms Corpuz rushed to two bedrooms on the second floor to alert five other occupants before she escaped through the back door with Madam Tan's father-in-law, Mr Tang Song Bak.

Six of the 10 occupants were able to evacuate by climbing out of their bedrooms before the Singapore Civil Defence Force (SCDF) arrived.

Mr Tang, who initially believed it was a small fire, hid in the master bedroom toilet with his wife and used wet towels to facilitate their breathing. Hoping to put out the fire, he filled a pail in the toilet and opened his room door, only to be confronted by thick black smoke. In a state of shock and panic, Mr Tang climbed out to the balcony and jumped off onto the porch, sustaining a head injury and an arm fracture. Only after jumping did he recall that his wife was still in the toilet.

Six pump ladders and five supporting vehicles were activated to put out the fire, which was eventually quelled at 6.45am.

Mr Johnson was found in the corridor next to a guest bedroom, while Madam Tan was inside the master bedroom toilet. They died from extensive burns. Both rooms were on the second floor.

Mr Johnson had reportedly reassured Mr Tang that it was safe to leave the batteries to be charged overnight as they had extra safety features. Mr Johnson was the co-director and designated technical expert of their company, and had attended a course in Germany on operating the drones.

However, the coroner had cautioned against leaving drone batteries or similar devices to charge overnight entirely unattended.

"Charging of batteries of drones ... should be done only with supervisory presence of persons who can intervene in the event of an exigency, such as an adverse reaction when the battery is overcharged or damaged," he said.