An Evolution of Scientific Mixed Gas Diving Procedures at the National Park Service Submerged Resources Center.

Abstract

The Submerged Resources Center (SRC) of the National Park Service has been conducting an assessment of sites of cultural significance in the Lake Mead Recreational Area since 2002. Many of the sites were flooded when Hoover Dam construction was completed and the reservoir filled, such as the aggregate plant and associated structures. Others have been deposited after Lake Mead filled, including a B-29 lost in 1948. Because many sites of interest are located at depths exceeding 150 ffw (45 msw), work initially began with ROV surveys. Later activity involved mixed gas training and in situ work with divers using heliox. Equipment profiles and techniques have evolved as subsequent phases of the project were fielded. Initially, open-circuit equipment was used, then mixed teams using closed-circuit rebreathers (CCRs) with the open-circuit divers, and most recently teams solely using CCRs. In addition to the SRC divers, participants from NOAA and NGOs have been involved. This paper will examine the background of the project, diving standards utilized for the heliox operations, and the procedures and safety concerns involved with teams using multiple modes of diving with mixed gas on these research operations.