Yeah, I wish I had a reference as it is pretty unbelievable. But I have heard it at several in person presentations. It also might not be all that unbelievable if only 15% (completely made up stat) of CCR divers use a checklist.
Did just find this reference here:
Staying Alive on Rebreathers: It Really Is All About Set-Up
I think I've also heard the same from Neal Pollock, and maybe Garreth Locke.
"Concannon, a speaker at Rebreather Forum 3.0 and a well-known attorney whose law firm has strong practice in sports and recreation law, sees the issue as a cultural one.
“I am certain that the fix does not require a redesign by mainstream manufacturers or changes in the training [curriculum] offered by established agencies: it’s much more straightforward than that. I believe we need to change the attitude of the average diver preparing for a CCR dive, and this change includes the use of a pre-dive checklist.”
During his law practice and work as advocate for several dive-industry clients (including CCR manufacturer AP Diving and training agency TDI), Concannon has investigated dozens of fatalities. “Striking in its absence in 100 percent of the cases I have seen that involved a rebreather is a physical checklist; no sign of one on the diver’s person, in his kit, on his rebreather.”
This, Concannon says, indicates a “cultural short-coming.”"
But if it is 100% or 90%, it doesn't matter. We need to use written checklists to prevent this type of incident. And we need to make it the cultural standard.