The French Decompression Tables (MT92 / 1992) are divided into 8 tables by working time:

• Table 1: less than 30 min
• Table 2: 30–60 min
• Table 3: 60–90 min
• Table 4: 90–120 min
• Table 5: 120–150 min
• Table 6: 150–180 min
• Table 7: 180–240 min
• Table 8: 240–480 min

Tables are defined for working pressures up to 4.8 bar in 0.15 bar increments. Real interventions rarely match exactly:

• Select a table whose pressure is equal to or immediately above the actual working pressure.
• Choose the time equal to or immediately above the actual working time.

A compensation table must always be available in case the scheduled working time is exceeded. The last time is listed separately as the extra for emergency tables (manual page 90).

At the start of decompression, the worker is decompressed to the first stage (or surface) at a constant speed.

• Maximum speed: 1000 hPa/min (1 bar/min)
• Value used in the tables: 300 hPa/min (0.3 bar/min)

• Stage time begins as soon as the worker reaches that stage pressure.
• The last minute of stage time is used to decompress to the next stage (or to atmospheric).
• Stage times are given in each table.

Principle. Breathing pure O₂ with a mask accelerates inert-gas elimination and reduces deco times. Especially suited for long air operations or significant pressures. The deeper the O₂ stage, the more effective — the 0.3 bar stage is combined with the 0.6 bar stage in all O₂ schedules.

Limits. Due to O₂ toxicity, mask-O₂ stages are limited to 1.2 / 0.9 / 0.6 bar. There is no 0.3 bar stage (combined with 0.6).

• O₂ percentage in the airlock atmosphere is limited to 25%.
• Continuously monitor the airlock O₂ rate during mask O₂ breathing.
• Masks must be equipped with an overboard dump.
• Ventilation flow should keep the airlock O₂ as close to 21% as possible.
• Any grease that may ignite under high partial O₂ pressures is strictly forbidden in the decompression airlock.

Breaks. O₂ stages require a 5-minute AIR break every 25 minutes. Stage times already include these breaks.

Compression. All compressed persons must equalize their ears correctly and must not exceed 3000 hPa/min (3 bar/min). Anyone failing to equalize must get an immediate equalizing stop and, if needed, a drop in pressure. If equalization is impossible, the person is decompressed and abandons the operation.

Tables. The tables give deco profiles by operating conditions (pressure, sickness, length of stay). If conditions could reduce safety, use the next greatest working time for an extra margin.

Initial vs successive operations.

• Surface interval: time between two interventions (end of deco → start of new pressurization).
• Initial intervention: no pressurized intervention in the previous 12 h.
• Repetitive intervention: surface interval < 12 h. Only allowed if pressure never exceeds 2.1 bar.
• If highest exposure > 0.75 bar in any 12-h period, only one repetitive intervention is possible and the next surface interval must be > 12 h.
• For repetitive deco: add the working times of both interventions; if pressures differ, use the highest reached.

The intervention report must include:

• Date of operation
• Names of workers and Lock Operator (with signature)
• Place of intervention
• Operating pressure
• Workers' surface interval
• Pressurization time (start of deco for max length of stay allowed)
• Type of work carried out
• Time decompression began
• Deco procedure used + breathing gas + arrival/departure time for each stage
• Names of personnel in attendance at the surface, etc.

The report is a working document — fill it in gradually during the operation.

• Poor physical condition, nervous tension
• Hyperthermia or cold
• Tiredness or accumulated intensive operation

Take these into account when choosing the table. If conditions could reduce safety, use the next highest working time for extra margin.

• No sustained physical effort (running, stairs, gym, etc.).
• Rest period on site:
  • Up to 20 min deco → 1 h rest
  • 20 min – 2 h deco → 2 h rest
  • Over 2 h deco → 3 h rest
• Worker must stay on site within easy access of the surface medical lock.

• Symptoms generally appear within 30 minutes of return to atmospheric pressure, but can appear up to 24 hours later.
• Longer delay → usually less severe.
• A fully operational recompression chamber must be available for 12 hours after the intervention.

• Operating pressures are gauge (relative).
• Tables assume surface atmospheric pressure of 1000 hPa (1 bar).
• Valid for altitudes 0–300 m and barometric variation 0–50 hPa. Outside these limits, apply an altitude adjustment.

• Time in minutes between the start of pressurization in the airlock and the start of decompression.
• Times are expressed in hours and minutes (00hr00).
• Use the same watch for all events.

Reference only. Always apply on AMP / DMO instruction. Pressures are relative (gauge) bar.

• (·) Period = 25 min breathing O₂ on the mask, then 5 min surrounding air.
• Continuous = continuous breathing of O₂ with the mask.
• Airlock O₂ must stay ≤ 25%; mask must have an overboard dump; no grease in the chamber.