A WOMAN who died while diving at the National Diving Centre in the Forest of Dean was using sub-standard breathing equipment, an inquest has heard.

Experienced diver Mary Restell 54, her husband Roy and a friend were using trimix, a mixture of three different gases, for the first time during the dive.

The inquest at Gloucester Coroner’s Court on Thursday (14th January) heard that she was using her own equipment and some of it was not up to standard.

The combination of trimix, which is more difficult to breathe than compressed air, and a regulator that was not functioning properly, led Mrs Restell to have breathing difficulties and become unresponsive deep under water at the former quarry.

On November 8th 2014, the couple met with good friend and diver Claire Boxall to plan the deep dive at the diving centre near Chepstow on November 15th, where she would dive with them. They had used the centre previously and knew the layout.

"It was the first time we had used tri-mix, a mixture of oxygen, helium and nitrogen, and the dive was scheduled to take 44 minutes," he said.

They descended to 60 metres together without incident, but when they started to swim back in the direction of the pontoon she seemed unfocussed and was making ineffective movements.

"She began to sink and I tried to manage her buoyancy as well as my own. There was no understanding in her eyes and although there was some water in her mask, she made no attempt to clear it," he said.

"Suddenly, she dropped below 60 metres and I saw a rush of air from her mouthpiece. She signalled that she could not breathe.

"The only thing I could do was to risk decompression sickness and the bends by taking her to the surface as quickly as possible."

The staff did their very best to to help Mary but she died at the scene, and although Roy suffered from the bends, he made a good recovery.

Expert witness Thomas Anthony, who provides technical support to Navy divers, was asked by the coroner to check all the equipment Mrs Restall had used.

He said it seemed as though she still had plenty of gas at the time of the incident, but two regulators in her equipment were not performing correctly and did not appear to have been serviced recently.

"This meant she would have to make a lot more respiratory effort to get the amount of gas she needed," he said.

"Also, the gas itself is dense and more difficult to breathe at that depth, which would have added to her problems.

"Because she had to work hard to breathe there would also have been a build-up of carbon dioxide (in her blood)."

He said all this seemed to fit with Mrs Restall becoming unresponsive at depth.

Summing up, the coroner said the cause of death was a gas embolism and a lung-related pulmonary barotrauma and pulmonary tumour.

Mrs Restell had been in good health before the dive but had died from a build up of gas in the blood, said the coroner.

“Joining all the facts together, there is only one conclusion I can come to, and that is the accidental death of a woman who had been doing something she loved,” she said.