INTERVIEW – In Hong Kong, workers at a hyperbaric site are under pressure for a month. A new organization of work that raises questions.
At a depth of 50 meters, in Hong Kong Bay, a gigantic drill slowly digs its furrow. By the end of 2018, an underwater tunnel will link the city to Landeau Island and its international airport. This ambitious project is being led by Bouygues Construction. To prevent the structure from collapsing under the pressure of the water, the air is compressed to five bars at the heads of the tunnel boring machine. Teams of tubists take turns every six hours to maintain them, then return to a pressurized “housing” to spend the night (see Bastien’s testimony). The mission lasts 28 days during which they will be kept permanently under pressure, with a gas mixture composed of nitrogen, helium and oxygen.
These extended stays make it possible to avoid the daily decompressions that hyperbarists undergo in occasional intervention. They also represent a considerable gain in productivity: the daily intervention time of agents is almost doubled. But is this method safer? If it has been experienced in the past, it has never been experienced on such a large scale for such a long time. Bernard Gardette, hyperbaric physiologist, former scientific director of Comex, specializing in underwater engineering, discusses this work organization.
Are hyperbaric stays really safer than one-off interventions?
Bernard Gardette: Yes, because divers or tunnel boring machines often carry out long and difficult operations. They have to decompress every day and thus put their body to the test. However, the risk of decompression sickness in professional diving, although rare (less than one in a thousand), increases with the depth, duration and arduousness of the site. Hence the interest in reducing the number of these decompressions.
The productivity argument has often been put forward – and it is well founded – but hyperbaric stays are also less risky for the health of divers. In addition, this four-week rotation organization was already used in the context of tunnel crossings in Germany a few years ago. The people who developed the procedures in Hong Kong were inspired by the German yard.
Decompression responds to global procedures, which have greatly improved since the 1970s. Obviously, they become less safe for very long or very deep stays, but this is not the case for the Hong Kong site, which is 50 meters long. depth. Overall, they remain reliable.
Bernard Gardette, hyperbaric physician: “ Tables have evolved a lot and are set up empirically. We go back half as fast today as 30 years ago “
Do we have hindsight on the effects of long exposure to a hyperbaric environment?
Bernard Gardette: Yes, because from the 1970s, on oil platforms, saturation diving (deep and lasting several days) gradually replaced intervention diving, until robots replaced men. Then it was used by the tunnel boring machines.
We know the pathologies linked to poor decompression, such as dysbaric osteonecrosis, recognized as an occupational disease. But this bone damage is closely linked to the fact that at the time, the decompression tables were put in place empirically, they were not as thin as they are today. Moreover, the number of cases is declining.
We have also observed accelerated pulmonary aging, neurological and memorization disorders in hyperbaric workers, but it is not known whether this is linked to saturation or difficult working conditions on sites (stress, noise, etc.). The link with hyperbaric stays has not been demonstrated.
Bernard Gardette : ” Whether you stay two hours or eight days, it’s the same thing, your body is saturated with gas. “
During long stays, were certain symptoms observed in hyperbarists?
Bernard Gardette: Throughout the studies, we mainly observed hygiene problems inside the box, which posed a risk of infection. When you are locked in a room, bacteria grow quickly and can be pathogenic. In our work, for example, we have shown that these bacteria are concentrated at very high levels in the shower curtain. Cleaning procedures have been developed; in particular, toxic products must be avoided because pressurized air increases the toxicity of detergents.
The other significant point is the psychological aspect. During these long stays, the hyperbarists live in groups, confined in a small space. It’s a bit like getting on a very small boat for a crossing of the Atlantic with strangers … There can be problems of mood and disagreement, reinforced by the voice distorted by helium, sometimes a source incomprehension.
>> Read more: “Hyperbarism: 28 days of work underwater”
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