Kym Brett Curnow and backpackers Thomas Leslie Butcher, Anna Sushchova Winther and Julia Kohrs-Lichte died on November 17, 2015, on Grigg Road in Scaddan during lightning-sparked bushfires in the Esperance area that lasted 11 days.

The cause of death could not be ascertained but each person was "extensively incinerated with severe thermal damage", counsel assisting the coroner Lyle Housiaux said on Monday.

The fire danger index rating forecast for that day was worse than the 2009 Black Saturday bushfires in Victoria, but the Department of Fire and Emergency Services only took over from the shire in the afternoon.

The blaze moved rapidly after it jumped containment lines and entered private property, travelling about 70km in five hours, Sgt Housiaux said.

A watch and act alert was issued at 1.10pm but was not upgraded to an emergency warning until 5.50pm.

At 2.45pm, the fire had reached the Karingal Pastoral Company farm, where Mr Butcher was a mechanic, Ms Winther a cook and Ms Kohrs-Lichte a chaser bin operator.

Owners David and Linda Campbell were friends with Mr Curnow, a farmer who was also an experienced firefighter.

Mr Curnow arrived about 3.30pm and suggested they leave, but the Campbells said they would defend their property, the inquest heard.

Mr Butcher was concerned for his friend's horse, Cougar, and decided to leave with the animal and women.

"It is not entirely clear why they turned left on to Grigg Road, as this decision took them into the path of the fire front, but it was known that this was the usual route Mr Butcher took when travelling to Esperance," Sgt Housiaux said.

Mr Curnow also turned left onto Grigg Road.

"He may have been going to check on his own property and family, or alternatively he may have been trying to stop Mr Butcher from driving east towards the fire," Sgt Housiaux said.

After travelling about 3.5km, it appeared Mr Butcher's vehicle was hit by the firestorm, veered off the road, smashed into trees then rolled.

Mr Curnow's vehicle also veered off the road after travelling about 3km, crashed into trees and was engulfed in flames.

Mr Curnow's remains were found in the back of his vehicle that evening.

The remains of Mr Butcher and Ms Kohrs-Lichte were found inside their vehicle and Ms Winther's remains were found outside.

Cougar died inside the horse trailer.

Sgt Housiaux said all had been "exposed to the full intensity of the fire".

Coroner Sarah Linton is examining whether the fires could have been predicted and/or prevented and why the victims left the relative safety of a farm in favour of trying to escape by driving away.

Australian Associated Press