I own a copy of the NOAA Diving Manual, 2nd edition, December 1979, which goes into the mechanics of mixed gas diving and various diluent gasses at some length. This resource would do little for your research in terms of historical genesis, except to illustrate that trimix was routinely in widespread use in the 1970's by scientific, military, and commercial divers.
A more useful reference for you would be the US Navy Diving Manual, Volume II, dated January 1977. This was the first time the Manual was divided into two Volumes: I was for air diving, Volume II covered mixed gas diving. A complete history of the development of mixed gas as a breathing media is presented, albeit in a concise format (five pages) in Chapter 9, pages 9-1 - 9-7. Googling on any of the inventors would likely provide you with additional information. One example may help you along:
"In 1924 the Bureau of Mines and the Navy joined to sponsor a series of experiments in the use of helium oxygen mixtures. The initial work was done at the Bureau of Mines Experimental Station in Pittsburgh, Pennsylvania. In 1927 the Navy shifted the operations of it's own Experimental Diving Unit (EDU) from Pittsburgh to Washington DC where the work continued. The first tests showed no detrimental effects on animals or humans from breathing a helium oxygen mixture" (US Navy Diving Manual, Volume II, 1977, pp 9-4). That should provide you with a few links to work with.
Yet another resource that may prove useful would be "Deep Diving" by Brett Gilliam, et al. (Watersports Publishing, 1992 and 1995). Gilliam et. al. offer different context regarding 'deep diving' with an emphasis on the historical development of mixed gas diving to conduct sport diving; and here is one point you may wish to ponder in your paper.
Clearly the US Navy has been using trimix since the 1930s in one form or another. Mixed gas diving did not achieve any sort of widespread legitimacy among sport divers, however, until the 1990s - 60 years later - although that date is relatively imprecise and may be debated by any number of specialists who may have been experimenting with mixed gas for cave dives, etc. in the late 1980s. Still, I do not consider such endeavors to constitute "widespread legitimacy" among sport divers.
The point is that the "invention" of trimix occurred in the late 1800s, it was first experimented with in the early 20th century (1919), and was first used (in the ocean) by military divers during a practical test when the submarine USS SQUALUS was salvaged from a depth of 243 fsw in 1939.
So you're going to need to clearly differentiate between "invention" (= discovery) of O2 toxicity and theories regarding mixed gases in the late 1800s (google on Henry Fleuss and Paul Bert); "invention" (= adoption) of mixed gas by the US Navy (1920s/1930s); and "invention" (= migration) of mixed gas to the international sport diver community at some point in the 1990s.
Still, I think you've chosen a very interesting topic and I wish you well with your paper.
Regards,
Doc
