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MN90 Tables

French Navy Tables 1990 — Official FFESSM reference for dive training

Recreational Air FFESSM

⚠️ Warning — These tables are for informational purposes only. They do not replace proper training or a dive computer. Ascent rate: 15-17 m/min. See How to read the tables.

Official source

French Navy tables (1990). Ascent rate: 15-17 m/min from bottom, 6 m/min between stops.

Max depth
65m
Entries
—
Ascent
15-17m/min
Stops
3-6-9m
Stop duration by depth
Main MN90 Table

How to read MN90 tables?

  • Depth — Maximum depth reached
  • Time — Bottom time (descent start → ascent start)
  • 3m, 6m, 9m — Stop duration in minutes
  • TDT — Total Decompression Time
  • DGL — Dive Group Letter (A to P)

Emergency procedures

Fast ascent (>17 m/min)

No symptoms: descend back to half-depth within 3 min, stay 5 min, then ascend normally.

Stop interruption

If <3 min at surface: descend and redo the full stop.

Understanding MN90 Tables: Complete Guide

The MN90 tables (Marine Nationale 1990) are the gold standard for dive training in France. Used by FFESSM for levels N2 through N4 and instructor certifications (E3, E4), they calculate mandatory decompression stops during ascent after air dives.

How they work

During a dive, nitrogen from compressed air dissolves into body tissues proportionally to depth and duration. MN90 tables model this absorption and indicate required stops at 3, 6, and 9 metres to allow nitrogen to safely off-gas, preventing decompression sickness (DCS).

Successive dives

After a first dive, residual nitrogen remains in your body. The Successive Dive Group (GPS), from A (low saturation) to P (high saturation), quantifies this residual loading. Before any successive dive, consult Table I (residual nitrogen) and Table II (time penalties) to determine the time penalty to add. A minimum surface interval of 15 minutes is required.

Conditions of use

MN90 tables are calculated for sea-level dives with compressed air (21% O₂, 79% N₂). They assume an ascent rate of 15-17 m/min from depth to the first stop, then 6 m/min between stops. Any different conditions (altitude, heavy exertion, cold) require additional safety margins.

FAQ — MN90 Tables

What is the difference between MN90 and MT2019 tables?
MN90 tables are designed for recreational air diving and are the FFESSM exam standard. MT2019 tables, published in the French Official Journal in 2019, are for professional diving and cover air, Nitrox, and Heliox mixtures with more conservative profiles.
How do I calculate stops for a successive dive?
Note your GPS from the first dive. Use Table I with your GPS and surface interval to find the residual nitrogen coefficient. Then cross-reference this coefficient with your planned depth in Table II to get the time penalty. Add this penalty to your actual dive time to read the stops from the main table.
What should I do if I ascend too fast?
If you exceed 17 m/min with no symptoms: descend to half your maximum depth within 3 minutes, stay there for 5 minutes, then ascend normally completing all required stops. If symptoms appear (tingling, joint pain, dizziness), administer O₂ and contact emergency services immediately.
Can MN90 tables be used at altitude?
No, MN90 tables are calculated for sea level. At altitude, the lower atmospheric pressure changes decompression calculations. Use altitude-specific tables or a dive computer with altitude compensation above 300m elevation.
Which FFESSM levels require MN90 knowledge?
MN90 tables are part of the curriculum starting from N2. N2 divers must read stops for a single dive. N3 must master successive dives (GPS, time penalties). N4 and GP must plan complex dives and manage emergency procedures. Instructors (E3, E4) must teach the complete table system.