Two friends died while diving in a disused quarry, a Gloucester inquest has heard.
The centre was closed while police and safety experts investigated
Janine Davison-Evans, 27, from Stockton-on-Tees and Hank Austin, 25, from Ascot, were found dead at the Diving Centre at Tidenham, Gloucs.
The inquest heard the pair visited the centre on 9 April, 2004.
Dr Ian Calder said Miss Davison-Evans died as a result of a difference in pressure between her lungs and the atmosphere. Mr Austin drowned.
The National Diving Centre's managing director Stuart Pelham-Davis told the inquest that the site, at the disused Dayhouse quarry, had been fully approved by the Health and Safety Executive and the Royal Society for the Prevention of Accidents.
The centre's duty manager Kieron Stringwell, an experienced diver, raised the alarm and searched for the missing divers after discovering their car.
He told the inquest how he found their bodies 65 metres below the surface of the water as he helped police with their search.
Mr Stringwell said: "I could see their bodies on a layer of crushed rock at the bottom of a wall. One diver was on top of the other they were both facing upwards."
The inquest heard the divers were both using air cylinders which are only recommended for depths of about 30 metres.
Mr Stringwell said that from below that depth the pressure made air toxic and a mixture of gases should be used.
Pathologist Dr Ian Calder said Miss Davison-Evans had died as a result of barotrauma - a difference in pressure between her lungs and the outside atmosphere.
He said: "The lungs tear as a result. The blood is just replaced by gas. It is a fairly catastrophic situation."
Dr Calder told the inquest the "primary cause" of Mr Austin's death was drowning.
The coroner recorded verdicts of accidental death.