---
title: "Depth limits"
description: "Reading the four numbers a mix is held to at depth, and every warning it can raise."
---

> Documentation Index
> Fetch the complete documentation index at: https://docs.divelogic.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Depth limits

import { GasCard } from "@/components/react/PlannerScreens";

Give the planner a mix, a depth and an oxygen ceiling and it answers with four
numbers and a list of warnings. That answer is the block on every gas card, and
the block the gas wizard shows at its limits and confirm stages.

## The four numbers

- **MOD**, the maximum operating depth, is where the mix's ppO₂ reaches the
  ceiling the gas is held to. It rounds down to the whole metre, never deeper
  than the real figure. A mix with no oxygen shows nothing here.
- **ppO₂** is the oxygen partial pressure at the depth being judged, in bar, and
  what the two oxygen warnings are measured against.
- **EAD** is the depth at which the mix's nitrogen load feels like air: helium
  and oxygen count as non-narcotic. It rounds up to 0.1 m, never less than the
  real figure. The wizard labels it **END**.
- **Density** is grams per litre at that depth, a work-of-breathing figure
  rather than a decompression one. See [Gas density](/theory/gas-density).

The planner picks the depth rather than asking: a back gas at the plan's maximum
depth, a staged gas at its switch or drop depth, anything else at its own MOD.
That is why the same 50 % mix reads differently on a deco card.

## The warnings

Six conditions, in this order. The two density conditions are mutually
exclusive, as are the two oxygen conditions.

| Condition | Severity | What you see |
|---|---|---|
| Density above 6.2 g/L | Error | `High gas density — exceeds 6.2 g/L` |
| Density above 5.2 g/L, at or below 6.2 | Warning | `Elevated gas density — exceeds 5.2 g/L` |
| Narcotic depth above 30 m | Warning | `High EAD — exceeds 30m` |
| ppO₂ above 1.6 bar | Error | `ppO₂ too high — exceeds 1.6 at depth` |
| ppO₂ above your own limit, at or below 1.6 | Warning | `ppO₂ exceeds target 1.4` |
| MOD shallower than the depth being judged | Error | `MOD (22m) is shallower than dive depth` |

**The 1.6 bar error is absolute.** It fires whatever ceiling you set on the gas,
so raising your own limit past 1.6 does not silence it. The 5.2 and 6.2 g/L
figures are the SPUMS advisory and the NEDU limit.

Analysis uses the conventional gas-planning pressure approximation rather than
the schedule's, so on an altitude or fresh-water plan a card's MOD and the
schedule's depths will not agree exactly.

## Next

[Switch depths](/gases/switch-depths) sets the depth at which each of these
numbers is judged, and the depth the gas becomes available at.

Source: https://docs.divelogic.ai/gases/analysing/index.mdx