Broome pearl diver Jarrod Hampton likely suffered an air embolism and could not have been saved in time, a doctor specialising in dive medicine has told a coronial inquest.

The evidence is significant because the company he worked for has been under scrutiny over its safety procedures and whether enough was done to help Mr Hampton.

The inquest in Perth is examining the 22-year-old's drowning on his second day at work for Paspaley Pearls while drift diving south of Broome in 2012.

Mr Hampton had been on his second last dive of the day when, witnesses have told the court, he suddenly surfaced, cried for help and then disappeared under the water again.

He was pulled to the boat by his air line but was unconscious and could not be revived.

Dr James Caruso is the chief medical examiner and coroner for the City of Colorado, an expert in hyperbaric medicine and former US Navy diver.

He was called as a witness by the pearling company.

Dr Caruso told the court evidence showing Mr Hampton rapidly ascended, had air bubbles in the left atrium of his heart, and surfaced and yelled out before losing consciousness pointed to an air embolism.

That is a condition where bubbles develop in the blood and lead to a heart attack or stroke.

"An air embolism [was] very likely the injury that resulted in drowning," Dr Caruso said.

Expert witnesses differ on cause of death

Paspaley lawyer Gail Archer asked Dr Caruso what Mr Hampton's prospects would have been if he had been wearing a buoyancy vest and was rescued when he first surfaced.

Dr Caruso replied it may have prevented him drowning, but it would not have stopped the effects of the air embolism.

He said patients with an air embolism needed recompression with 100 per cent oxygen in a hyperbaric chamber as soon as possible, especially if they were unconscious.

It took five hours for the pearling boat Mr Hampton was on to reach Broome after his death.

Dr Caruso said his chances of surviving in that time were "vanishingly remote".

"It's likely if you went several hours in the long transition, you are delivering a deceased diver to the chamber," he said.

Dr Caruso's evidence contradicted that given by Carl Edmonds, another doctor specialising in dive medicine, who said an air embolism was unlikely.

Dr Edmonds also said when Mr Hampton had lost hold of his work line on a dive before the fatal dive, he likely took some water into his lungs, and this would have predisposed him to greater risk on following dives.

"The conclusion would be he had some degree of hypoxia, which would mean he was very vulnerable," he said.

Paspaley Pearls has since made buoyancy vests mandatory for divers on its pearl boats.

The inquest continues.