Hello,
There are some naïve interpretations of Gavin's data appearing here.
What the QinetiQ database shows is that if the gas density rises beyond 6g/L during realistic levels of exercise underwater there is a markedly increased risk of the diver developing a hazardous degree of CO2 retention. That does not mean they WILL die, or that there WILL be some sort of accident. Moreover, there is a lot of individual variability in disposition to develop high CO2 levels when the density and work of breathing increase. Some divers will maintain a normal CO2 even under these circumstances. So, of course there will be a huge number of examples of divers / dives where the density was higher than 6g/L with no obvious adverse outcome.
However, there have almost certainly been more deaths among the "cause unknown" cohort due to this problem than we realise. AND if you are a responsible organisation formulating recommendations for application by the wider diving population, it would be very unwise to ignore a risk factor such as this which is defined by hard data. Those of you validating diving dense gas by pointing out that you do it with no problems, or claiming that if it was bad then there would have been more deaths are completely missing the point.
Simon M