Tools
Gas Specs
Analyse any nitrox or trimix mix at any depth: PPO₂, equivalent air depth (EAD), equivalent narcotic depth (END), gas density, and maximum operating depth (MOD).
Senast uppdaterad 29 september 2026
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What it is
Gas Specs takes a breathing mix and a depth, then tells you everything that matters about how that gas behaves there. Where Best Mix designs a blend for you, Gas Specs analyses one you already have. Set the oxygen and (for trimix) helium fractions, set the depth, and read the numbers.
The in-app title is “Gas Specs” (the same name appears on the home card and in the header). Internally the tool is the gas analyzer at the plan/ead-ppo2 route, so older references to “EAD/PPO₂” or “Gas Analyzer” point at this same screen.
How to use it
Set the oxygen
Add helium if it's trimix
Set the depth
Read the stats panel
Every input card has both a slider and a tap-to-type number field with plus and minus steppers, so you can drag for a quick estimate or type an exact figure. O₂ runs 5 to 100%, He 0 to 100%, and depth 1 to 300 m. The tool opens at air (21% O₂, 0% He) at 12 m. The field you are typing into stays above the keyboard.
O₂ and He can’t add up to more than 100%, so raising He lowers O₂ to fit. If that pushes O₂ under 5%, every figure in the panel shows a dash and the alerts wait until the mix is back in range.
Depth follows your unit setting, so the slider reads in metres or feet. PPO₂ is always reported in bar, never converted.
What each output means
Each value shows a short field label, with the descriptive phrase as a smaller subtitle beneath it.
| Output | Shown in app | Meaning |
|---|---|---|
| Oxygen partial pressure | PPO₂ (bar value) | Partial pressure of oxygen: PPO₂ = FO₂ × absolute pressure. The toxicity number. |
| Equivalent air depth (EAD) | EAD (subtitle “Equivalent air depth”) | The depth at which plain air gives the same nitrogen loading as your mix. Lets you reuse air-based no-deco thinking on nitrox. Helium is excluded. |
| Equivalent narcotic depth (END) | END (subtitle “Equivalent narcotic depth”) | The air-equivalent depth for narcosis. Tells you how clear-headed the mix keeps you at depth. |
| Maximum operating depth, working | Working MOD (subtitle “PPO₂ 1.4”) | Deepest depth at a 1.4 bar working limit, for active swimming. |
| Maximum operating depth, deco | Deco MOD (subtitle “PPO₂ 1.6”) | Deepest depth at a 1.6 bar limit, for resting and deco stops only. |
| Gas density | Gas Density (g/L value) | Real density of the mix at depth. Dense gas is hard to breathe and traps CO₂. |
| Equivalent air density depth (EADD) | EADD (subtitle “Density Equivalent”) | The depth at which air has the same density as your mix, a quick read on breathing effort. |
| No-decompression limit (NDL) | NDL (minutes, subtitle “No-stop time, GF 80”) | Minutes you can stay at this depth on this mix before a decompression stop becomes mandatory, at your default GF high. See No-stop time. |
| Minimum breathable depth | Min Depth (subtitle “Hypoxic”) | For hypoxic mixes only: the shallowest depth where PPO₂ reaches the 0.16 bar floor and the gas is safe to breathe. |
The panel shows both MODs at once: a Working MOD at PPO₂ 1.4 and a Deco MOD at PPO₂ 1.6, so you can see the active-swim limit and the deco-stop limit side by side without changing a setting.
No-stop time (NDL)
The NDL stat is the no-decompression limit: how many minutes you can stay at this depth on this mix before a decompression stop becomes mandatory. The Deco Planner’s engine (Bühlmann ZH-L16C) descends from the surface on this mix at your default descent rate, then counts from the moment you arrive. It is the same figure the Deco Planner shows on a level of that depth and gas. It uses your default gradient factors from Manage → Settings → Deco Planner, and the subtitle names the GF high it used (“No-stop time, GF 80”). With the stock GF 50/80 and air, 30 m (100 ft) gives about 10 minutes.
- A dash means the figure is still being worked out, or the engine could not answer.
- ∞ (“No limit”) means the model sets no practical limit at this depth, as in the shallows on air.
- 0 min (“Deco stop required”) means a stop is already mandatory on arrival.
Narcotic-gas assumptions
EAD and END both convert a partial pressure back into the depth on air that would produce it, using the absolute pressure for your water type:
- EAD uses the nitrogen fraction only. It finds the depth at which air’s nitrogen partial pressure matches your mix’s, then reports that depth. Helium is treated as non-narcotic and excluded, since EAD measures nitrogen loading (your decompression reference), not narcosis.
- END depends on whether you count oxygen as narcotic. This is the Treat O₂ as narcotic toggle in Settings → Diving. With it off, only nitrogen narcoses, so END equals EAD. With it on, everything except helium narcoses (nitrogen plus oxygen), which raises your END at the same depth. Turning it on is the more conservative reading.
Gas density uses standard surface densities (O₂ 1.429, N₂ 1.251, He 0.1786 g/L) scaled by absolute pressure, then by the water temperature. Those constants are measured at 0 °C (32 °F), so the reading is multiplied by 273.15 / (273.15 + T), where T is the Water temperature you set in Settings → Diving (default 15 °C / 59 °F). Gas gets thinner as it warms, so a warmer setting reads lower. The 5.2 and 6.2 g/L limits below are published figures and do not move with the temperature, which means a warmer setting warns a little deeper. EADD compares the mix against air’s surface density and is a ratio, so the temperature cancels out of it.
Warnings
The stats carry status colours and the screen raises alerts for the dangerous cases:
- High PPO₂. Above the 1.4 bar active limit the tool flags the value as deco-only and warns to avoid it during active swimming. Above 1.6 bar it warns of seizure and blackout risk.
- Gas density. Above 5.2 g/L it cautions and suggests adding helium. Above 6.2 g/L it warns of CO₂ buildup and tells you to add helium or reduce depth. Both limits are user-adjustable defaults (5.2 and 6.2 g/L), set in the deco and gas defaults.
- Hypoxic mix. If PPO₂ falls below the 0.16 bar breathable floor the tool marks the mix hypoxic and shows the depth above which it’s unsafe to breathe.
The O₂ and He sliders cannot produce an impossible mix. Raising O₂ past 100 − He percent automatically lowers He (and raising He past 100 − O₂ percent lowers O₂), so the two fractions always sum to 100% or less.
Behaviour and limits
On a tablet held in landscape the screen splits into two columns: the O₂, He and depth sliders on the left, the stats panel and any warnings on the right. Each column scrolls on its own. On a phone, or on a tablet held upright, the tool stays one scrolling column.
Gas Specs reflects only the numbers you type in. It assumes the mix is exactly what you entered, so analyse and label your real cylinder before diving.
Related
- Best Mix Calculator designs the mix that Gas Specs analyses.
- Deco Planner uses the same PPO₂ and MOD logic to schedule gas switches on a full dive.
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