Section 6.00 – Nitrox Diving

This section describes the requirements for authorization and use of nitrox for Scientific Diving.

6.10 Requirements for Nitrox Authorization

Prior to authorization to use nitrox, the following minimum requirements must be met:


Only a certified Scientific Diver or DIT diving under the auspices of the MBL is eligible for authorization to use nitrox.

Application for authorization to use nitrox must be made to the DCB. Submission of documents and participation in aptitude examinations does not automatically result in authorization to use nitrox.  The applicant must convince the DCB through the DSO that they are sufficiently knowledgeable, skilled and proficient in the theory and use of nitrox for diving.


In lieu of writing/promulgating AAUS specific training standards for Nitrox divers, AAUS references the standards for Nitrox diver training as defined by the WRSTC and/or ISO.  AAUS programs who wish to train Nitrox divers may do so using one of the following options:

  • a) Under the auspices and standards of an internationally recognized diver training agency.
  • b) Under the auspices of AAUS using the minimum guidelines presented by the most current version of the RSTC/WRSTC and/or ISO Nitrox diver training standards.

“Minimum Course Content for Enriched Air Nitrox Certification” – World Recreational Scuba Training Council (WRSTC),

“Recreational diving services- Requirements for training programs on enriches air nitrox (EAN) diving”. ISO 11107:2009 – International Organization for Standardization (ISO),

Practical Evaluation

  • Oxygen analysis of nitrox mixtures.
  • Determination of MOD, oxygen partial pressure exposure, and oxygen toxicity time limits, for various nitrox mixtures at various depths.
  • Determination of nitrogen-based dive limits status by EAD method using air dive tables, and/or using nitrox dive tables, as approved by the DCB.
  • Nitrox dive computer use may be included, as approved by the DCB.
  • A minimum of two supervised open water dives using nitrox is required for authorization.

Written Evaluation

  • Function, care, use, and maintenance of equipment cleaned for nitrox use.
  • Physical and physiological considerations of nitrox diving (eg.: O2 and CO2 toxicity)
  • Diving regulations, procedures/operations, and dive planning as related to nitrox diving
  • Equipment marking and maintenance requirements
  • Dive table and/or dive computer usage
  • Calculation of: MOD, pO2, and other aspects of Nitrox diving as required by the DCB

6.20 Minimum Activity to Maintain Authorization

The diver should log at least one nitrox dive per year.  Failure to meet the minimum activity level may be cause for restriction or revocation of nitrox authorization.

6.30 Operational Requirements

Oxygen Exposure Limits

  • The inspired oxygen partial pressure experienced at depth should not exceed 1.6 ATA.
  • The maximum allowable exposure limit should be reduced in cases where cold or strenuous dive conditions, or extended exposure times are expected.

Calculation of Decompression Status

  • A set of MBL/DCB approved nitrox dive tables should be available at the dive site.
  • Dive computers may be used to compute decompression status during nitrox dives. Manufacturers’ guidelines and operation instructions should be followed.
  • Dive computers capable of pO2 limit and fO2 adjustment should be checked by the diver prior to the start each dive to ensure conformity with the mix being used.

Gas Mixture Requirements

  • Only nitrox mixtures and mixing methods approved by the MBL/DCB may be used.
  • MBL personnel mixing nitrox must be qualified and approved by the MBL/DCB for the method(s) used.
  • Oxygen used for mixing nitrox should meet the purity levels for “Medical Grade” (U.S.P.) or “Aviator Grade” standards.
  • In addition to the AAUS Air Purity Guidelines outlined in Section 3.60, any air that may come in contact with oxygen concentrations greater than 40% (i.e.. during mixing), must also have a hydrocarbon contaminant no greater than .01 mg/m3.
    • For remote site operations using compressors not controlled by the MBL where this is not verifiable, the DCB must develop a protocol to mitigate risk to the diver.

Analysis Verification by User

  • Prior to the dive, it is the responsibility of each diver to analyze the oxygen content of his/her scuba cylinder and acknowledge in writing the following information for each cylinder: fO2, MOD, cylinder pressure, date of analysis, and user’s name.
  • Individual dive log reporting forms should report fO2 of nitrox used, if different than 21%.

6.40 Nitrox Diving Equipment

Required Equipment

All of the designated equipment and stated requirements regarding scuba equipment required in the MBL/AAUS Manual apply to nitrox operations. Additional minimal equipment necessary for nitrox diving operations includes:

  • Labeled SCUBA Cylinders in Accordance with Industry Standards
  • Oxygen Analyzers
  • Oxygen compatible equipment as applicable

Requirement for Oxygen Service

  • All equipment, which during the dive or cylinder filling process is exposed to concentrations greater than 40% oxygen, should be cleaned and maintained for oxygen service.
  • Any equipment used with oxygen or mixtures containing over 40% by volume oxygen must be designed and maintained for oxygen service. Oxygen systems over 125 psig must have slow-opening shut-off valves.

Compressor system

  • Compressor/filtration system must produce oil-free air, or
  • An oil-lubricated compressor placed in service for a nitrox system should be checked for oil and hydrocarbon contamination at least quarterly.