Decompression sickness during construction of the Great Belt Tunnel, Denmark

Thirteen cases of decompression sickness (DCS) occurred during the construction of the 8-km long railway tunnel under the Great Belt in Denmark between January 1992 and February 1996. 320 compressed air workers were subjected to 9018 pressure exposures in four tunnel boring machines. Overall DCS incidence was 0.14%. Working pressures ranged between 0.25 bar (1.25 atm abs or 126.3 kPa) and 2.95 bar (3.91 atm abs or 396.3 kPa) and working times ranged between 2 minutes and 339 minutes. During the first 1798 pressure exposures 7 DCS cases occurred using French air decompression tables from 1974. The following 7220 exposures were then decompressed in accordance with the newly issued French air decompression tables of 1992. After changing schedules 6 DCS cases occurred and DCS incidence was reduced to 0.08%. Two of the first seven DCS cases had permanent residual symptoms after recompression treatment. All DCS cases, except one, occurred among the 30% of exposures that imposed the greatest decompression stress. DCS incidence among these exposures was 0.42%.