After descending to the anchor, which was in 18 metres of water, the first group, of which I was a member, proceeded to the cave and tunnel. After about 15 minutes, when exiting the top of the tunnel, I sighted the other group approaching the tunnel's bottom entrance which is 26 metres deep. Approximately 10 minutes later I saw the female and one male making a rapid blue water ascent with the other male following below. My group started our scheduled ascent during which we saw the surfaced divers return to the boat. While we were doing a safety stop at three metres, two masks were seen to fall from the rear of the boat. The remaining diver from the second group retrieved one and one of my buddies the other.

Upon surfacing we found the boat's skipper administering oxygen to the female. This was the first indication that there was any real problem. The skipper advised us that he had called the Port Hacking rescue vessel, Rescue 2. One of my buddies, who was an ambulance paramedic, took over treatment of the patient.

I was advised by the female's two buddies that after descending right to the bottom, the female's submersible pressure gauge was fluctuating wildly as she breathed. The two males had no appreciation of what this meant so they continued the dive. Approximately 20 minutes into the dive, she began having difficulty with insufficient air being supplied by her regulator. This difficulty rapidly increased to such an extent that she could not breathe. One of her buddies then began buddy breathing with her (neither of the two males had octopus regulators). They began an ascent and the male vented both BCDs to slow ascent as they surfaced. The ascent from 20 metres took slightly less than 60 seconds.

The boat's skipper had immediately noticed their problem and had called the rescue boat via radio. He got the distressed female back on board and, as indicated above, administered oxygen.

I checked the female's equipment and found that she had 100 bar of air remaining in her tank and that both her second stages were working correctly. However, I noticed that when I took a breath, her submersible pressure gauge registered a slight fluctuation. I immediately suspected that the tank valve was only partially opened. I discovered that I could not turn the valve in either direction. The male who did the emergency ascent advised me that he had turned the valve on and had opened it fully.

Later examination showed that not only was the valve very stiff, it had probably completely malfunctioned and would not open even if the knob was turned the full three turns. Even when it was turned, it took over one full turn before the valve opened even slightly and air was able to enter the pressure gauge. It did not appear to open past about one and a half turns. This was checked a number of times. It appeared that the valve was faulty and only opened a small way.

Within five minutes Rescue 2 arrived and they advised that the Westpac Rescue Helicopter was on its way from Prince Henry Hospital, Little Bay.

` Although the female was not suffering any apparent injury (she was conscious and alert), the crew of Rescue 2 decided that it would be better if she was transferred to their boat and transported to nearby Jibbon Beach where she could be examined by the helicopter's doctor. The helicopter was on site within a few minutes and a crewman was dropped in the water so he could board the boat. The helicopter landed the doctor at the beach where he met the boat. Apart from a headache, he found that the female had no apparent problems but he decided to transport her by helicopter to the hyperbaric unit at Prince Henry Hospital. A section of beach was cleared of sunbathers by Police (who had just arrived) and rescue crew. After being placed in a stretcher, we assisted loading the female into the helicopter which had landed on the narrow beach.

The female was flown to Prince Henry Hospital where she was placed in the hyperbaric chamber and recompressed for four hours. A more detailed examination at the hyperbaric unit had shown that she had probably suffered a minor air embolism in the brain. She was kept in the hospital for 30 hours for observation. It is probable that the headache she suffered was caused by a combination of the stress of the incident and the lack of air during ascent.

What lessons can we all learn from this incident?