Decompression sickness in surface decompression breathing air instead of oxygen

We report an unusual decompression sickness (DCS) incident in a commercial diving project. Eleven divers completed 91 dives to 23.5-36.2 m with bottom times ranging 23-67 min. The divers were breathing compressed air while immersed. Decompression was planned as surface decompression in a deck decompression chamber breathing oxygen typically for 15-30 min. Due to a technical error the divers breathed air rather than oxygen during the surface decompression procedure. Two divers suffered DCS. Both were recompressed on site with the same error resulting in them breathing compressed air rather than oxygen. One of them experienced a severe relapse with cardiovascular decompensation following recompression treatment. While DCS was expected due to the erroneous decompression procedures, it is noteworthy that only two incidents occurred during 91 dives with surface decompression breathing air instead of oxygen. Accounting for this error, the median omitted decompression time was 17 min (range 0-26 min) according to the Bühlmann ZHL-16C algorithm. These observations suggest that moderate omission of decompression time has a relatively small effect on DCS incidence rate. The other nine divers were interviewed in the weeks following completion of the project. None of them reported symptoms at the time, but five divers reported having experienced minor symptoms compatible with mild DCS during the project which was not reported until later.