Michael Müller has been diving since 1972 and has specialized in building and diving with oxygen rebreathers since 2003. Recently, he wrote an article about the lost oxygen rebreather of Hans Hass. This article describes in detail the composition of this unique early rebreather. I am very grateful to Michael for granting permission to publish this article on my website.

Für die Deutschsprachigen unter Ihnen ist der Originalartikel am Ende dieses Artikels in deutscher Sprache verfügbar.

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A technically minded hobbyist, scuba diver and enthusiastic user of bubble-free oxygen diving equipment tells the story of

‘Agaïs 1942’

The lost first oxygen rebreather from Hans Hass

article by Michael Müller

To get straight to the point: There is no specific designation for Hans Hass’s first diving apparatus. The name “Aegean 1942” was coined by me. I have long been involved with rebreathers, and I wanted to give his very first diving apparatus a special name because it has unique technical fundamentals and other features that we no longer find in later diving equipment in this form. Hass primarily focused on the advantages of bubble-free diving at that time. An oxygen apparatus offered the best conditions for this. Thus, the type “Aegean 1942” was created in collaboration with Drägerwerk. My goal was to trace this link from the diving rescuer to today’s commonly used oxygen rebreathers.

Submarine diving rescuers and small submersibles before 1941

The predecessors for this diving apparatus were the submarine rescue devices built by Drägerwerk at the time. They were designed to rescue crews from sunken submarines, and were perfectly constructed for this purpose. The breathing bag was arranged around the neck and the upper chest area, which changed the body’s center of gravity, making them suitable only for vertical, rapid ascent, but not for free swimming. After surfacing, they guaranteed a safe, unconscious position. The fact that pure oxygen was breathed had an impact on the depth from which one could ascend; experiments showed that even at a depth of 100 meters, it was possible to breathe pure oxygen safely for five minutes, and at 50 meters for 10 minutes.

The small diving devices from Drägerwerk were essentially the same devices but could be used for underwater work at shallow depths, such as ship maintenance or seabed tasks. The diver was weighted with iron sandals, a so-called tail weight chain, and a neck weight to walk on the seabed. Both devices operated on the pendulum breathing principle, where the gas is exhaled through a single hose, passing through the soda lime canister into the flexible breathing bag, and inhaled back through the same hose to the diver. The soda lime absorbs the carbon dioxide, and the spent oxygen is replenished from a compressed gas cylinder. The smallest device of this type allowed for approximately 30 minutes of underwater activity.

The rescue collars were typically made from reddish-brown rubberized fabric and closed with a clamp fastener at the bottom. The front part of the collar housed the “Kali cartridge,” containing the soda lime in a disposable cartridge, as well as a 0.4-liter oxygen cylinder with a pressure of 150 atm without a pressure reducer. The valve of the oxygen cylinder was manually operated to control the flow within limits. A pressure reducer was not required.

Hans Hass, who had previously undertaken his first diving adventures free-diving or with a surface-supplied, open-bottom diving helmet, sought a swimming diving device after his Caribbean expedition to ease his underwater activities. Recognizing the potential of these devices, he initiated the development of a corresponding swimming diving device at Drägerwerk in Lübeck after a test in the diving tank in 1941. He convinced the company that underwater research and swimming diving were essential for the discovery of new raw material and food sources and that such an oxygen diving device would also be advantageous for military purposes.

For this purpose, he met several times in 1941 with the then chief engineer Hermann Stelzner from Drägerwerk, who unfortunately passed away in the office on October 19, 1942, just two hours after completing the last sentence of the second edition of his book “Diver Technology.”

Oxygen Rebreathers

The principle of oxygen devices had been known for years. Without going into details about the advantages and disadvantages, there are two basic design principles: the pendulum breathing devices, whose operation has already been described above, and the oxygen rebreathers, which are of interest to us here. In these devices, the breathing gas is controlled by check valves and conducted through two breathing hoses. The valves are arranged so that inhalation occurs through one hose and exhalation through the other. The carbon dioxide is absorbed in the soda lime, and the used oxygen is replenished in the breathing circuit via a compressed gas cylinder.

Since Hans Hass, as a researcher, publicist, and filmmaker, focused primarily on biological relationships and the depiction of underwater natural beauty, the technical development of the oxygen rebreathers he used, particularly in the early years, is scarcely documented. Unfortunately, the first device no longer exists. Only a few photos of it have survived.

The lost first prototype, model “Aegean 1942”

In 1942, Hans Hass conducted his first expedition to the Aegean Sea with the expedition ship “Universitas.” On July 12, the newly developed swimming diving device by Drägerwerk was used for the first time by Ari Rosini, allowing him to breathe freely while moving almost weightlessly underwater. Unfortunately, only extremely blurry photos and general descriptions from various Hans Hass books are known for this device. However, this device represents the transition phase from the diving rescuer to the first swimming diving device, requiring special attention. The following description is based on video clips from the Hass film “Men among Sharks,” as well as previously unknown and unpublished color slides that are housed in the Hans Hass Institute, led by Michael Jung.

Breathing bag (counterlung)

In developing this swimming diving device, Hermann Stelzner built on the experiences with the diving rescuer. The breathing bag was moved to the back, allowing it to be used for swimming diving in any body position. At the front was a chest apron with the oxygen cylinder, which was equipped with a pressure reducer or dosing valve.

The following drawing shows the basic structure of the device:

No reference to counterweights is found in the literature that had to compensate for the buoyancy of the breathing bag. We therefore do not know whether any were planned or not. It is possible that lead plates were present, as in the subsequent Dräger rebreathers, which were then attached directly below the breathing bag. For this reason, we have not depicted any counterweights in our illustration.

The breathing bag, also known as a breathing sack or counter lung, is made of the same material as the diving rescuer and the small diving devices. It consisted of characteristic reddish-brown rubberized fabric and was closed at the bottom with a clamp fastener. Below it, on the right and left, are the attachment eyelets known from the diving rescuer. There was no overpressure valve to release the oxygen expanding in the counter lung during ascent. Instead, the gas was allowed to escape “through the corners of the mouth (past the mouthpiece), as well as through the nose” (H. Hass in “Contribution to the Knowledge of Reteporidae”) over the diving mask.

Lime Container and Double Breathing Hose

Inside the breathing bag is the lime container. It appears to be non-refillable and uses the disposable cartridges known from the small diving devices, with a usage duration of one hour.

Since the issue of pendulum breathing and the associated CO2 accumulation in the breathing hose was already known at that time, Stelzner and Hass used the following trick: They split the breathing hose shortly after the soda lime cartridge using a Y-piece. Inside it (not in the mouthpiece) were mica check valves, so the inhaled breathing gas was directed through one hose to the mouthpiece, while exhalation went through the other hose back to the soda lime cartridge. The cartridge itself, as with the diving rescuer, was flushed twice by the breathing gas, achieving an effective double cleaning of CO2. The main differences from all known subsequent models are the disposable soda lime cartridge and this Y-piece. This device thus represents the link between the pendulum breathers and the modern rebreathers, where the breathing gas passes through the lime container only once.

Mouthpiece

The same mouthpiece as used in the diving rescuers was employed. It featured a built-in shut-off valve (plug valve) and was complemented by an attached V-shaped manifold for the double corrugated hoses.

Oxygen Cylinder

Initially, an oxygen cylinder with a capacity of 0.6 liters and a pressure of 150 atm was used, providing 90 liters of oxygen, which lasted up to an hour. Later, in “Men and Sharks,” Hass mentioned a 0.8-liter cylinder with 200 atm. Regardless, the cylinder of the swimming diving device, like the diving rescuer, was filled by simply overflowing from a large reserve cylinder, with the subsequent pressure increase achieved using a Dräger hand filling pump.

Pressure Reducer

A key change compared to the diving rescuer is the presence of a pressure reducer. This ensures a constant flow rate of about 0.9 liters per minute, which corresponds to the average resting consumption of a human. In his dissertation, Hans Hass mentions one liter, though he mistakenly states per second, which would have emptied the cylinder in just one and a half minutes. To allow for increased oxygen demand and buoyancy control, the regulator also has a bypass valve, which can manually supply oxygen as needed. Hans Hass refers to this as the “button.”

These pressure reducers were already available and used by Drägerwerk for self-rescuers in mining, for instances of entrapment or exposure to toxic atmospheres. For example, they were present in the Model 180 from 1938. The pressure reducer only needed to be modified for underwater use. It was fitted with a 90-degree elbow in the high-pressure area and a hose connection to the breathing bag in the low-pressure area.

Use and Whereabouts

At the beginning of the Aegean expedition, only one piece of the described swimming diving device existed, which Hans Hass himself used. A second copy was sent later. With these devices, Hans Hass conducted a series of self-experiments, particularly regarding the possible diving depths. Regularly, depths of up to 20 meters were reached, which corresponded to the officially approved maximum depth limit at that time. In the film “Men among Sharks,” Hass mentions a maximum achieved depth of 35 meters. Considering the current limit of 6 meters for recreational divers, this is quite an extreme value! Indeed, there were at least two diving accidents that Hass survived only by luck. Once, due to high partial pressure during deep diving, he suffered from oxygen toxicity called hyperoxia, and once, due to low partial pressure during ascent, he suffered from hypoxia, a lack of oxygen. In “Men and Sharks,” he describes the condition at a depth of five meters as “like a light switch had been turned off inside me…”. Subsequent color photographs from the Hans Hass archive show detailed images of the type “Aegean 1942” for the first time:

It appears that no example of the very first device “Aegean 1942” has survived, as almost all the equipment from the Aegean expedition fell victim to the chaos of the war and post-war period. The expedition ship “Universitas” exploded as a munitions ship…

Outlook In all subsequent expeditions, Hans Hass used more modern rebreathers without a Y-piece, which combined the separate breathing hoses. The first and oldest surviving example of these is located in the Aquazoo/Löbbecke Museum in Düsseldorf. The author was able to identify at least three different stages of development, including the “Model 138” sold in the Federal Republic by the company Barakuda for 490 marks, which was used in the first “Xarifa” expedition.

Eventually, due to the fatal accident of Jimmy Hodges on a “Xarifa” expedition, Hans Hass largely stopped using oxygen rebreathers and switched to compressed air diving equipment. He conducted over 2000 dives to depths of up to 20 meters with oxygen rebreathers.

At the annual meeting of the Historical Diving Society in 2014, the author will present a functional replica of this interesting “Aegean 1942” device.

For further reading:

1. Chief Engineer Gustav Ryba: Handbook of Mine Rescue Services, Volume II, Arthur Felix Publishing, Leipzig, 1930.
2. Hermann Stelzner: Diver Technology, Charles Coleman Publishing, Lübeck, 2nd Edition, 1943.
3. Various books by Hans Hass.

Michael Müller, born in 1958, electrical engineering graduate. Inspired by books by Hans Hass, he began snorkeling in 1972. His first experiences building his own camera housings, UW photography  Open

circuit diving with the GST since 1974. 1980 First self-built single-hose automatic, from 2003 Construction of rebreathers, which he uses almost exclusively almost exclusively in extremely shallow water.

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Michael, auch im Namen aller Taucher möchte ich dir sehr für deine Forschungsarbeit und deine Erlaubnis danken, diesen fantastischen Artikel mit den Lesern meiner Website zu teilen!

Michael, also on behalf of all divers, I would like to thank you very much for your research work and your permission to share this fantastic article with the readers of my website!

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