Air Supply Cuts Off When Regulator Failed

A diver’s regulator suddenly failed and cut off air supply, even though there was still a third of the air pressure remaining in the tank.

Reported Story

I was diving with a regulator which I had purchased eight months earlier. It was the first dive of the day and I entered the water at approximately 7:45 am (with 2910 psi, 200 bar) at which time I descended to a depth of 91 ft (28 m) looking for sharks.

Relatively quickly, I left this depth and made my way shallower to an average depth of around 60 ft (18 m) and was photographing along the way. I was diving solo, however there were approximately 16 other divers on the dive at various points along the wall. I passed another photographer in order to stay out of his shot and went on a bit further. Upon seeing a fan that I wanted to photograph, I did what I always do. I looked at my computer to check my air and depth. At that time I was at approximately 53 ft (16 m) deep with approximately 1100 psi (75 bar) in my tank.

Regulator Failed, Air Cuts Off, Cut Off Air Supply

I took several shots of the fan. I remember completing a big exhale when I finished and righted myself to begin swimming on. However, when I tried to take a breath, there was nothing. I immediately grabbed my octopus, expecting I would get some air, but there was absolutely nothing – no air at all. I did a 360 in the water to see if I could see someone close enough to help and saw the diver I had just passed. I quickly motioned to raise his attention, but he wasn’t looking up and I believed he was too far for me to risk swimming toward him. I made the decision to do an emergency assent to the surface. I was already having the involuntary “pulsing” urge to breathe by this time. At some point, I looked at the computer and it read 000 time/air remaining.

On the way to the surface, I tried again to breathe, but there was zero air. When I popped up at the surface, the dinghy was very close to me so I quickly got in. I was telling the driver that I ran out of air and had to do an emergency assent, and that I needed to be put on oxygen. At this point, I grabbed for my dive computer and it read 900 psi. I was confused by this (because I saw it at 000) and I tried both regulators again, but neither would breathe. I remember showing him the computer and saying something like “There IS air in the tank!”

Upon arriving at the resort, the dive manager put me on oxygen for about 20 minutes or so. I, along with others, watched as he immediately checked my regulator on another tank. I believe it breathed maybe once on the full tank, however not on any partial tank. He took the tank I was using, and in front of everyone, he examined it thoroughly and there was nothing wrong or unusual with the tank. I used this tank the rest of the trip with a new first stage and everything worked fine.

The boat manager tested my system again after the next dive by having someone come back with 900 psi. It continued to fail, and would not breathe.

I sat out of diving for about 30 hours and went back with a new first stage system. I had no other incidents with the new first stage, and I was using the same tank that had been used with the failure. I believe this clearly was a catastrophic failure of my regulator first stage, and it failed closed.


Scuba regulators work on a “downstream” principle, where the air flows down from a high pressure to an intermediate pressure and then down to a low pressure. Because of this they are often thought of as “fail safe” because many failures will cause a free-flow of air rather than cut off the air supply. Indeed, it is very rare for a first-stage to fail in the way this diver described.

This particular first stage has an Automatic Closer Device to seal the first stage when it is taken off the tank, to prevent water getting into it. After initially reporting the incident on the DAN Incident Reporting System (DIRS), the diver followed up to report, few months later, to advise that the manufacturer has posted a “Consumer Safety Notice” on their website, recommending a “voluntary product check” because a component of that system may not have been tightened to the correct torque, leading to “a possible gas flow failure during a dive”.

Any diver who owns a regulator that has an automatic closer device should check the manufacturers website for product safety notices.

“Solo” diving, or diving without a companion close by, has gained popularity in recent years since the “self-reliant diver” certification courses became widely available. A core element of many of these courses is the adoption of a redundant air source, in case a failure such as this occurs. Unfortunately though, this diver was not carrying a redundant air source and needed to make an emergency ascent. Luckily it was the first dive of the day and the diver had moved to shallower water during the dive.

~ Peter Buzzacott, MPH, PhD