[abstract] DECOMPRESSION TABLES FOR THE WESTERN SCHELDT TUNNELING PROJECT.

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[abstract] DECOMPRESSION TABLES FOR THE WESTERN SCHELDT TUNNELING PROJECT.

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Title: [abstract] DECOMPRESSION TABLES FOR THE WESTERN SCHELDT TUNNELING PROJECT.
Author: Sterk, W; van Rees Vellinga, TP
Abstract: INTRODUCTION: Two tunnels under the Western Scheidt are being constructed, with a length of 6.6 kilometers and to a maximum depth of approximately 60 meters, using a hydroshield boring technique. This is the first time that this technique is used to such a depth in a soft ground river delta area. Occasional human compressed air work was expected to be necessary. The greatest pressure to be encountered was estimated as 6.5 to 8.5 bar (G). The 1993 Dutch DCD caisson decompression tables were chosen for the conventional air range to a pressure of 3 bar (G). As much higher pressures were to be encountered, several procedures common in diving were planned, as use of trimix and saturation techniques. As often, the engineers underestimated the necessity of human interference under pressure. The project started in July of this year, without the necessary measures being completed to use advanced diving techniques. METHODS: As work progressed, the air tables had to be extended. For this purpose, the computational model that generated the NDC diving tables was used in a more conservative version. Tables were calculated up to 4.5 bar (G), using oxygen from the 1.5 bar stop on in steps of 0.3 bar to the surface, interrupted by regular air breaks. RESULTS: So far, 94 man exposures in the range to 3.0 bar and 387 exposures between 3.0 and 4.2 bar were done, with bottom times of 19-240 minutes, without any signs of DCS. However, symptoms of nitrogen narcosis were experienced at pressures over 3.6 bar, interfering with work performance. Also, one worker had some minor symptoms of long term oxygen toxicity. Although Doppler bubble detection was planned, this could not be realized so far because of operational circumstances. CONCLUSIONS: The extended decompression tables for compressed air work appear to be reliable, but this has to be confirmed by future Doppler bubble detection. To prevent nitrogen narcosis, advanced diving techniques should be used in compressed air work for pressures exceeding 3.6 bar.
Description: Undersea and Hyperbaric Medical Society, Inc. (http://www.uhms.org)
URI: http://archive.rubicon-foundation.org/5820
Date: 2000

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  • UHMS Meeting Abstracts
    This is a collection of the published abstracts from the Undersea and Hyperbaric Medical Society (UHMS) annual meetings.

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