The aim was simple – executing it wasn’t. To successfully dive below 1000ft and demonstrate humanity’s ability to explore the depths of the continental shelf.

The problem? This was 1962. The dive pushed technology, human physiology and the contemporary understanding of decompression theory to its absolute limit. The endeavour was heralded for its scientific achievement but would sadly claim the life of one of its participants. The co-founder of the British Sub-Aqua Club, Peter Small.

Peter Small had been instrumental in the growth of scuba diving in the UK. A journalist for national newspapers and magazines, he brought the new and exciting sport of scuba diving to a mainstream audience. 

The incident was headline news at the time but has since faded into diving lore. To me, it perfectly encapsulates the spirit of the early diving pioneers. 

The Plan

The mission’s architect was Swiss mathematician Hannes Keller. Keller had been working closely with Dr Albert Bühlmann researching the effects of different breathing gases on the body. Bulhmann, who would later become synonymous with the decompression algorithms that bear his name, was an expert in the cardiovascular system at the University of Zurich.

Together they performed numerous experiments investigating the physiological impact of different gases including helium, nitrogen and even argon. The exact composition of these experimental mixes and the results were kept a closely guarded secret. 

As this was the 1960s, the experiments weren’t purely theoretical. Keller himself was lowered to 120m in Lake Zurich in a converted oil drum. Barely making it back alive, the dive was nonetheless considered a success and the pair continued with further dives pushing ever deeper.

Their progress drew attention from the US Navy, who saw the potential applications of their research, provided funding and resources to support a headline-grabbing dive to 1000ft (303m). That depth also corresponded with the approximate depth of the continental shelf, another useful soundbite for any marketing team. The US Navy’s interest in deep diving is obvious but Keller and Bühlmann’s research was also closely watched by NASA. Decompression illness is a significant concern for astronauts and any breakthroughs would of been helpful to the ongoing Space Race.

Peter Small, as a prominent figure in the diving community and a well-known science journalist, was an ideal addition to the team. When Small heard of the project he asked to join immediately. 

The Descent

The team travelled to Santa Catalina Island, off the coast of California, to carry out the dive. The influx of US Navy funding allowed Keller to design and build a small diving bell, named Atlantis, that would support the divers during their descent and the long period of decompression on the slow return to the surface.

The cramped bell was only 2 meters high and 1.5 meters in diameter, with a small hatch at the bottom to allow the divers to exit. It was pressured with ordinary air, to save the cost of using helium, with the divers using small sets they would refill throughout the dive with the variety of mixes Bühlmann and Keller had meticulously planned.

A test dive was performed 2 days before the 1000ft dive. Atlantis was lowered to 100m with both divers successfully swimming outside the bell and testing their equipment for an hour. This is likely the first time any diver had stayed so deep for so long. On return to the surface, Small complained of muscle pains, most likely decompression sickness, but appeared to recover quickly. The 1000ft dive would continue as planned but it proved an ominous sign of things to come.

On the 3rd December 1962 the team sailed from Catalina Island to attempt their record-breaking dive. Keller’s surface crew, including Dr Bühlmann, would run the operation from the support vessel Eureka, supplied by another interest party: the Shell Oil Company. 

Initially, the dive started well. A successful equipment check was carried out at 5m, with everything appearing in order, and then the descent began in earnest as the Eureka payed out the cable lowering the Atlantis into the deep. The first sign of any abnormality occurred during the descent – Keller noticed that the bottom gas mixture was only showing 80 bar instead of the expected 150. With the press and dignitaries in attendance the decision was made to press on but reduce their planned bottom time at 300m from 5 to 3 minutes.

The Atlantis’ descent eventually stopped with the small bell hanging in the darkness just above the sea bed at a depth of 309m.   

Problems

Keller moved quickly to exit the bell carrying ceremonial US and Swiss flags. He aimed to plant them into the seabed but immediately encountered problems on entering the water. The flags wrapped themselves around his mask and hoses. Struggling, Keller fought to free himself and after a couple of minutes both managed to re-enter the Atlantis.

Exhausted and disoriented, both men attempted to close the hatch and allow its controlled ascent to the surface. However, Keller’s fin became stuck in the hatch and the two men couldn’t clear it. Keller removed his mouthpiece, exposing himself to the rich air in the bell, and immediately passed out. Peter Small kept his in place, connected only to his own set – a decision that would prove fatal.

Within 30 seconds of re-entering the bell both men were unconscious. Keller experienced hallucinations from the extreme partial pressure of oxygen (at 300m it was well over 6 ATA) from the air he was now breathing. Around half an hour passed before Keller regained consciousness. It took Small almost 90 minutes before he came round, exhausted and unable to stand, he still appeared in relatively good health.

The team’s support divers, Richard Anderson and Christopher Whittaker, now faced the unenviable task of trying to close the fouled hatch of the Atlantis. With the hatch ajar, the bell couldn’t be raised to the surface without risking it flooding and severely compromising the planned decompression schedule.

Whittaker bravely made two consecutive dives to 60m attempting to close the hatch. He didn’t return from his second attempt and was never seen again. The hatch was eventually closed by Anderson, giving the occupants precious time to continue their decompression.

As the prolonged decompression continued, Small appeared to enter a restless sleep. The bell was recovered and as it was craned onto the pier Keller checked on Small and realised he wasn’t breathing. Keller attempted mouth-to-mouth. 

Atlantis was opened with Small immediately evacuated to a nearby US Navy hospital ship. He was pronounced dead on arrival.

What went wrong?

An inquiry was held and agreed on the cause of death: Peter Small died of a severe gas embolism likely caused by his depressed respiration while unconscious. It noted the negative impact of press and commercial interest – a familiar tale whenever there’s an incentive to just press on regardless of risk.

The inquiry determined what had happened, but failed to explain the why. Why did two experienced divers struggle to perform tasks at the bottom and what drove them to unconsciousness that would eventually lead to Peter Small’s death? 

This is often where the story ends, but to really understand what may have caused the tragedy off Catalina island, you have to look at Keller and Bühlmann’s secret gas mixture and dive schedule. The exact profile and gas mixes of the dive were not publicised and only became available a number of years after the fateful dive. 

If a contemporary understanding of gas theory is applied it gives a fascinating insight into the challenge the two men unknowingly faced. 

The Secret Mixes

The key to understanding what Keller and Bühlmann were attempting lies in a journal article they co-wrote two years after the incident off Catalina. ‘Deep Diving and Short Decompression by Breathing Mixed Gases’ appeared in The Journal of Applied Physiology and gives an excellent summary of their theory. 

The aim was to move from helium to nitrogen as the diluent during the ascent of the dive. As a lighter molecule helium is absorbed into and out of the body faster than the heavier nitrogen. If these physical properties are managed an optimal decompression schedule could be achieved.

In short they were trying to validate the benefits of isobaric counterdiffusion (ICD) in reducing decompression times.

As shown in the table, Small and Keller were exposed to partial pressures of Oxygen far above the recommended upper limit of 1.6 ATA that is accepted today. They were using full face masks that mitigates some of the risk associated with an ‘O₂ hit’ and potential seizures. Oxygen toxicity was already well understood at this time but the accepted safe limits were far higher than today. Peter Small himself described the absolute limit of air diving as 90m in his own book Your Guide to Underwater Adventure published in 1957. 

Keller was exposed to wildly high levels when removing his face mask inside the bell, suffering severe seizures, but is unlikely to have played a direct role in the accident.    

One implication of uber-deep diving with helium that was not understood at the time is High-Pressure Nervous Syndrome (HPNS). The condition causes symptoms such as decreased mental function, dizziness, visual disturbances and tremors when helium is used a breathing gas. Symptoms normally present on dives below 150m and appear to increase in frequency and severity with depth from there.

At over 300m, with Keller reporting tremors, confusion and the feeling of fear it is likely HPNS played a role in both divers’ ability to perform tasks and deal with incidents at that depth. The only methods for preventing the condition is by slowing the rate of compression (i.e. a slow descent) and using another inert gas, like nitrogen, in the breathing mix. None of these methods were known or used at the time.

The only guidance I could find on acceptable descent speeds to that depth are published by the US Navy for saturation diving. They recommend no faster than 0.6m per minute at depths to 300m. Keller and Small completed their descent in 30 minutes so around 10m per minute.    

The final significant consideration for their breathing gas was its density. At extreme depth the density of a breathing gas really matters. As the density of the gas increases so does the body’s effort to breathe eventually reaching a point it is unable to exhale the CO2 generated by the effort of breathing. The recommended safe density of a breathing gas is 6g/l, the bottom gas Keller and Small used was 8.9 g/l rising to over 11 g/l during the ascent phase.

Final Thoughts

Keller and Small were attempting a dive that would be fraught with risk today but in 1962 it was perilous. Looking back with a modern lens it’s unlikely Keller and Small knew the true risks they were taking. The absolute limit achieved open circuit diving, nearly 70 years later, is still around the 300m mark.

Hannes Keller’s contribution to the science of diving was significant but the death of Peter Small and Christopher Whittaker left it somewhat tarnished. His reputation remained nuanced up to his death in 2022.

The BSAC stands as a lasting legacy to Peter Small’s numerous achievements in diving (most of which haven’t been covered here). Within the club he’s remembered in an annual award bearing his name that celebrates excellence in underwater exploration. 

Peter Small didn’t live to see the scientific results of the dive. However, they are found on the wrists of most divers to this day. The culmination of Dr Bühlmann’s research was the decompression algorithm used by nearly every dive computer today.