19/12/2025
Is Trimix the New Nitrox? Thoughts on BSAC’s Deeper Diver Course
For a long time, trimix has been treated as something other in diving — technical, specialist, and only appropriate once a diver crosses a certain invisible threshold.
BSAC’s new Deeper Diver course takes a noticeably different approach, and I think it’s worth discussing.
The comparison that keeps coming to mind is nitrox in the early 1990s. Once controversial, nitrox eventually became normal not because it pushed depth, but because it improved understanding and reduced risk. It standardised the thinking, and divers then applied that thinking to dives they were already qualified to do.
Deeper Diver hopes to do something similar for deeper diving and helium.
BSAC has always permitted air, and later nitrox, to 50m. That hasn’t changed. What has changed is our understanding of narcosis, gas density, CO₂ retention, and cognitive performance at depth. It extends what a Sports Diver is already qualified to do by giving them the tools to make better-informed gas choices - air, nitrox, or trimix all the way to 50m.
Trimix is constrained. Oxygen must be no less than 20%, helium is capped at no more than 40%, and the maximum PO₂ is 1.4. This isn’t hypoxic trimix and it isn’t about extreme depth. It’s about managing narcosis and gas density sensibly, within clear guardrails.
Crucially, the course doesn’t mandate helium. It aims to educate divers so they can understand that there may be better options, and to understand the risks and trade-offs properly.
That approach is quite different from traditional trimix pathways, which are usually framed as explicitly technical, or from systems like GUE, where helium is normalised but only within a complete technical framework. Deeper Diver sits somewhere else: education first, progression second.
That said, I don’t think the course is beyond criticism. Personally, I think there’s a strong argument that it could sit at Sports Diver rather than Dive Leader, and I’m not entirely convinced by the pricing of the course pack relative to its content. Those points don’t undermine the intent, but they do affect accessibility.
Full transparency: my name appears in the Deeper Diver instructor manual as one of the authors. That’s exactly why I think it’s important to be open about both what works and what could be improved.
Whether you agree or not, I think this course marks an interesting moment in how we talk about deeper diving, gas choice, and education. I’m genuinely interested in hearing thoughtful perspectives from others.
