ABSTRACT
Tunnelling by the hydroshield technique requires workers to be exposed to overpressure for the inspection and repair of cutting tools. For decompression purposes, we used the Bühlmann model ZH-L16 which was specially adapted to meet the needs of the construction site. In order to examine the validity of the model we retrospectively evaluated 1,961 overpressure exposures (OEs) registered during the first phase of construction, which ranged from 1 to 3.4 bar. Exposure times varied widely from 5 to 455 min. and decompression times from 3 to 271 min. The overall rate of decompression sickness was 0.56% (11 cases: 4 knee pains, 4 shoulder pains, 1 shoulder-chest pain, 2 skin bends. There were no central nervous lesions). Four of the cases happened within the highest pressure range of 3.0 - 3.4 bar (101 OEs), 3 within the next lower range of 2.5 - 2.9 bar (180 OEs) and 3 within the remaining pressure ranges (1,762 OEs). Therapeutic recompression with pure oxygen proved successful in all cases. In conclusion, we consider the Bühlmann decompression model to be a satisfactorily appropriate procedure for construction sites. One important risk factor for decompression incidents seems to be an uncomfortable body position resulting from a cramped air lock. A more spacious one should therefore be mandatory.
