---
title: "Oxygen time limit"
description: "Reading how long the NOAA table allows at one ppO₂, and how long until the single-day OTU limit."
---

> 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.

# Oxygen time limit

import { OxygenTimeScreen } from "@/components/react/ToolScreens";

Oxygen time limit answers *how long can I stay at this ppO₂?* It returns the
NOAA single-exposure time for one partial pressure of oxygen, the time at which
the CNS clock reaches 100 %, and the time to the single-day OTU limit.

## What you enter

- **From**: **ppO₂**, to type the partial pressure, or **Mix and depth**, to
  have the tool work it out.
- **ppO₂** (bar): the partial pressure breathed.
- **Oxygen** (%) and **Depth** (m): shown instead with Mix and depth. The ppO₂
  assumes salt water at sea level.

There is no time field: the time is the answer.

## Reading the result

- **Single-exposure limit** (min): the main figure, the NOAA time allowed at
  this ppO₂ in one exposure. It reads **No limit** below 0.5 bar.
- **300 OTU in** (min): how long until the pulmonary dose reaches the
  single-day limit, or **Never** below 0.5 bar.
- **ppO₂** (bar): the partial pressure used.

This tool reports times, not a judgement, so its figures carry no rails or
colours. The verdict restates the main figure, for example *At 1.40 bar, one
exposure reaches 100 % CNS after 150 minutes.* Between the table's rows the
tool works the time out from the rows either side.

## What shortens the limit

- **Earlier exposure.** The times are for one exposure from a clean start.
  Oxygen already breathed the same day, on this dive or an earlier one, leaves
  less. The planner accounts for it; this tool does not.
- **ppO₂ above 1.6 bar.** The NOAA table stops at 1.6 bar. Above it the tool
  holds the 1.6 bar figure of 45 minutes, which overstates the time allowed.
- **Reaching the limit.** 100 % CNS is the end of the tabulated allowance, not a
  target. The planner warns from 80 %.

## Next

- [CNS and OTU](/tools/cns-and-otu) reads the exposure for a set time.
- [Oxygen exposure](/theory/oxygen-exposure) covers the clocks on a whole plan.

Source: https://docs.divelogic.ai/tools/oxygen-time-limit/index.mdx