Oxygen Exposure Calculator (CNS & OTU) – Free Nitrox Tool for Divers

Use oxygen exposure calculator to dive with sharks Protea Banks

African Dive Adventures™ provides advanced scuba diving tools for divers worldwide.

Oxygen exposure calculator helps divers track CNS percentage and OTU exposure when diving with Nitrox, allowing safer dive planning and oxygen management.

Advanced Oxygen Exposure Calculator for Scuba Diving (CNS & OTU)

Oxygen exposure calculator helps divers estimate CNS percentage and OTU loading across multiple Nitrox exposure segments. Use it to model repeated exposures, apply surface interval decay and track a running day total for more advanced enriched air dive planning.

Advanced CNS / OTU Calculator

Enter up to four exposure segments. The tool applies a simplified surface interval decay model to the running CNS total and calculates cumulative OTUs for the day.

Segment 1

Segment 2

Segment 3

Segment 4

Day Exposure Summary

Final running CNS: 47.3%
Estimated cumulative CNS after entered segments and surface interval decay.
Total OTUs: 52.8
Estimated total OTU loading across all active segments.
Lower oxygen exposure range
This tool uses a simplified planning model for public web use. It does not replace training, dive computer algorithms, agency procedures or conservative judgement underwater.
CNS limits are estimated from interpolated NOAA-style single exposure values between PPO₂ 0.6 and 1.6. Residual CNS decay is modelled using a simple 90-minute half-life approximation across surface intervals.

Oxygen Exposure Calculator

This oxygen exposure calculator helps divers track Central Nervous System (CNS) exposure and Oxygen Tolerance Units (OTU) when diving with Nitrox. Monitoring oxygen exposure is essential for staying within safe limits and reducing the risk of oxygen toxicity during single or repetitive dives.

What is CNS in scuba diving?

CNS (Central Nervous System oxygen exposure) measures the risk of acute oxygen toxicity during a dive. It is expressed as a percentage, with most recreational diving limits set at 80% (recommended) and 100% (maximum).

What are OTUs?

OTUs (Oxygen Tolerance Units) track long-term oxygen exposure, particularly over multiple dives or repeated diving days. OTUs are used to monitor cumulative oxygen loading and reduce the risk of pulmonary oxygen toxicity.

When should divers monitor oxygen exposure?

  • Repetitive Nitrox diving over multiple days
  • Deeper dives approaching MOD limits
  • Long bottom times on enriched air
  • Liveaboard or multi-dive trips
  • Technical or extended range dive planning

Oxygen safety reminder

An oxygen exposure calculator should always be used alongside MOD limits, dive computer settings and conservative dive planning. Divers must monitor PPO₂ throughout the dive and stay within training limits at all times.

Build a Complete Nitrox Dive Plan

Oxygen exposure is only one part of safe dive planning. Combine this tool with Nitrox planning, nitrogen management and gas consumption tools.

Nitrox Calculator Calculate MOD and best mix for enriched air diving. Equivalent Air Depth Calculator Understand nitrogen exposure when diving with Nitrox. SAC / RMV Calculator Plan gas consumption and improve dive safety. Scuba Diving Tools and Calculators Explore the full dive planning toolkit. Protea Banks Dive Map Understand dive sites and reef structure. Shark Diving Calendar Plan the best time to dive with sharks.

Frequently Asked Questions

What is a safe CNS limit?

Most recreational guidelines recommend staying below 80% CNS during a dive, with 100% considered the maximum exposure limit.

What happens if CNS is too high?

Exceeding safe CNS limits increases the risk of oxygen toxicity, which can lead to serious underwater complications including convulsions.

Do OTUs matter for recreational divers?

OTUs are more relevant for repetitive diving and multi-day dive trips, where cumulative oxygen exposure becomes important.

For Nitrox training standards and oxygen safety guidance, refer to your certifying agency such as PADI.