Snorkel vs freedive risk

Risk score is a heuristic 0–100 derived from six weighted factors. Depth is the dominant factor: pressure at 10 m is double surface pressure (1 bar per 10 m descent), and every additional 10 m roughly doubles the risk of an arterial gas event. Breath-hold time matters because hypoxia onset is non-linear — most untrained breath-holders hit a blackout-prone CO₂ curve at 60–90 s, regardless of how fit they are.

Site type layers on environmental risk: a Fiji lagoon (Mamanuca sheltered side, Beqa Lagoon) is dramatically calmer than Somosomo Strait on an incoming tide. Finning intensity is a proxy for oxygen consumption — sprint finning at 10 m burns your gas budget 2–3× faster than calm finning at 4 m. Experience is the trained-vs-untrained gap, which is the single biggest cause of shallow-water blackout (SWB) in the 6–12 m band — exactly where tourists dive.

Buddy presence is your rescue probability multiplier: an unconscious freediver at the surface with a buddy gets rescued in <30 s. Alone, that statistic jumps past the 4-min brain-damage window. Bands: 0–25 Very Low · 25–50 Low · 50–70 Moderate · 70–85 High · 85+ Critical.

• Not medical advice. If you have cardiac, pulmonary, or sinus conditions, consult a dive physician — even for the snorkel.
• Doesn't model ear / sinus equalisation problems. If you can't clear your ears in a Y-regulator check on the surface, freediving is off the menu.
• Doesn't account for cold water. Fiji is warm — but a 27 °C thermocline at 25 m on the Bligh Water still slows your CO₂ response.
• Doesn't predict marine-life encounters. Shark encounters during breath-hold freediving are rare but handled differently — operators brief you on the day.
• Not for scuba. The depth-time-pressure model for compressed-gas diving is different. Use a separate scuba planner (e.g. SSI / PADI table or a computer).