Review of excursion procedures used in commercial heliox saturation diving

Introduction: This study reviews heliox saturation procedures used in offshore commercial diving and focuses on bell excursion dives. It excludes initial compression and final decompression. Our first objective was to trace the history and the reasons behind the successive changes that led to the current practice. Our second objective was to review the current practice and identify problem areas and perspectives. Methods: We first present the background of excursion diving and reference key procedures from the US Navy, Comex, and international standards. We then review the procedures of 13 anonymised diving companies and compare their sources, designs, and operation parameters. Results: The current excursion procedures are derived from a few original procedures (US Navy, Comex). It appears that, without relevant scientific support since the 1980s, companies have empirically adapted these procedures to their needs. Two designs prevail: excursions from storage depth and excursions from the deepest depth. Recent innovations offer ‘standard’ and ‘extended’ excursions, sliding excursion windows, as well as shallow and deep excursions. Companies participating in the study have a low risk of DCS with excursion diving. Excursions rarely produce immediate DCS symptoms but associated bubble formation could impact the final decompression. The trend is towards reduced excursion distances and explicit post-excursion intervals. Oxygen toxicity remains a general concern in saturation diving, but the PO2 values used in the procedures reviewed are unlikely to cause pulmonary toxicity according to the dose models in use. Conclusions: We observed a trend towards harmonisation under the pressure of international standards and through cooperation within industry association committees. We recommend scientific monitoring of saturation divers to measure the decompression stress and support further research and development. We recommend that companies document their procedural developments to record and thus keep the lessons learned.