Changes and comments

Changes and comments

The 6th edition is now submitted to the printing office!

The sixth edition has now (May 29th 2024) been submitted, in Norwegian as well as English language,  to the printing office. I expect it to be returned within the next few weeks. Once received we will release the PDF version (free of charge) online as well

We circulated the draft 6th edition of the NDTT in February 2023. We have received a large number of comments (THANK YOU!). The inclusion of changes has been realtively straightforward, but we wanted to list each comment and provide a response in English to each of them in English. The translation and written response to each comment has taken a long time to complete, but finally it is finished.

In the right panel you may download the latest draft of the 6th edition. This is not the final version and though changes are minor compared to the official version, this draft should not be used for operational purposes.

Main changes in the (draft) 6th edition of the NDTT


The next edition will hold a bottom text on each page identifying the edition/Revision. (Rev A) We have expanded the explanation of table safety. Though the tables are expected to have a 2-5% DCS incidense when tested scientifically, real-life operational incidense will be a 10-order less (e.g. 0.2-0.5%). The reason for this is that actual diving will normally not "dive out" the tables, additional decompresssion will typically be added as a personal measure for added safety and due to under-reporting (Rev L).


A short description of  adjustments introduced in the NDTT relative to the original US Navy Diving Manual Rev 7 has been provided. (Rev A).

We have explained that though the expected DCS incidense of these tables are in the order of 2-5% when tables are tested scientficallye, the operational expected incidense will be tenfold less (i.e. 0.2-0.5%) due to the fact that tables seldom are "dived out", extra decompression is commonly added as a personal safety measure and due to underreporting (Rev L)

Standard air table

We have received a suggestion for describing decompression procedures for depths between the 3 msw intervals. A practical example: No-decompression limit for a 15 msw dive is 90 min and 60 min for a 18 msw dive. By interpolationj a no-decompression bottom time limit for a 16 msw dive would be 90 min. We have not taken position to this suggestion and in addition to the safety aspect we would like to know whether there is a real operational need for such interpolation. Please contact us if you have any opinion on this matter!

We have removed the previous reccomendation for a day without diving after three consecutive days of diving with at least one strenous dive. Data suggest that multiday diving has an acclimatizing rather than a sensitizing effect on DCS  (Rev H).

Dive computers

This chapter held contents mainly relevant for recreational diving. For this reason we have decided to remove it.

Diving at altitudes above 250 m

The flowchart has been revised to correct for an error related to N2 group addition for short acclimatization to height (corrrect value 7h10 min rather than 16h as presented in the previous flowchart) (Rev F).

Flying after diving

Serial 9, second sentence shold read: "The rules for flying after diving should be respected for all exposures to heights exceeding 1750 m asl.

Serial 12, the text in Ed 5 last paragraph should read (changes marked in bold types: "The diver has a Repetitive Group Designator of “B” from the preceding dive giving a penalty of 15 min to the 18m table. The repetitive group designator should be calculated for a bottom time of 35 min (15 min penalty + 20 min actual bottom time). A 35 min bottom time at 18 m will cause a Repetitive Group Designator of “F”."  (Rev B)

There is no reason to respect a minimum stand-off time before returning by helicopter if the helicopter can descend during the return flight and no additional altitude is required (Rev L).

Multilevel diving

There are a number of printing errors in the Norwegian version of the multilevel diving tables (serial 9). 

Page 17, Serial 4, fifth bullet: The dive should be completed with a 3 min safety stop.... (Previous edition "5 min") . The examples (serial 7 and 8) have been corrected with respect to the length of the safety stop (Rev G).

The prohibition for maximum Repetitive Dive Group of N has been removed - this did only affect maximum stay at the 12 msw stage with 10 min and the regulation did not add in any practical term to increased safety. It is stressed that shallowest stage/level is 12 msw (Rev L).

Oxygen toxicity

A spelling error ("OUT" rather than "OTU" has been corrected in Serial 9. (Rev D).
The example (serial 12) provided incorrect decompression advice as decompression was based on a table depth of 30 msw rather than the correct 24 msw EAD. This in turn affected the total OTU calculation since 12 m decompression is 15 min rather than 30 min as suggested in Rev 5 (Rev G)

The full chapter has been revised and UPTD/OTU has been replaced with ESOT (Rev O).

Diving with Nitrox

At present the tables advice pO2 not to exceed 1.5 Bar during the bottom phase and 1.6 Bar during decompression. Should this be reconsidered? IMCA and USN has 1.4 Bar as a threshold value for breathing gas in the bottom phase.

The recommendation to restrict Nitrox mix for SurDO2 to Nitrox36 has been removed - there was no particular reason to impose this restriction (Rev L).

Standard air decompression tables

We have received a suggestion of inclusion of a formula/equation or alternatively a seaparate table that will allow preparation of no-decompression dives for smaller depth increments than 3msw. A practical example:  Maximum allowed bottom time for a no-decompression dive according to the 15 msw table depth is 90 min. The similar no decompression time for 18 msw table depth is 60 min. If the diver plans for a dive to 16 msw he/she will be restricted to a bottom time of 60 min for such a dive. However, if the bottom time is calculated as a linear interpolation, a bottom time of 80 min would be acceptable. The authors have not taken a position to this request, but we would appreciate any comment as to the operational use for a separate table for no-decompression dives rated in 1 msw steps in table depth.


We have been questioned regarding correct decompression procedures in the event that there is a need for work at shallow depths at the end of a SurDO2 dive. If the bottom time call for a an in-water decompression stop (12m or deeper) work would not be allowed at shallower depth. However, for those dives where no in-water staged decompression stop is called for, the diver may finish the dive at depths not shallower than 6m. Surface interval should start to run once ascent to surface starts. However, for some of the long bottom times, work shallower than 12m is prohibited. These bottom times are indicated by italic typeset in the SurDO2 table. (Rev C)

A table has been inserted to facilitate identification of Nitrox dives profiles that may exceed daily limits or call for two days off diving after a given period of successive days of diving (Rev K).

The recommendation to restrict Nitrox mix for SurDO2 to Nitrox36 has been removed - there was no particular reason to impose this restriction (Rev L).

Prevention of Decompression sickness

The two tables have been simpliefied. In NDTT Ed 5  work at bottom depth was categorized as Low, medium or high. In the next edition this is reduced to two categories: "Low/Medium" and "High" (Rev I)

The general advice to avoid streneous physical activity for 3h after a dive has been modified for divers involved in the armed forces and emergency services. Such divers should limit the Repetitive Dive Group to "H" if a streneous activity is expected in the 3h post-dive period (Rev K).

Diving depth listed in the table for bottom time restrictions should be interpreted as equivalent air depth when nitrox is used according to Norsok U-100 and U-103 (Rev L and M).

Deep chamber dives

The particular deep chamber dive profiles (60 and 90 msw air exposures) have been removed. We have added a recommendation to let subjects exposed to deep chamber dives, for the purpose of experiencing Nitrogen narcosis, to breathe oxygen at 9 msw stops and shallower. 

Procedures in the case of omitted decompression or uncontrolled ascent (+last page)

We discovered 1.11.19 that a printing error has caused page 109 and 110 to be incorrect. Page 109 holds the procedures in the case of omitted decompression or uncontrolled ascent, while the very last page only holds the ISBN number. Corrected pages can be downloaded here. The printshop has now (Dec 2019) replaced page 109 with the correct one..

Decompression with closed bell (TUP)

The authors were approached aug 2019 by the Norwegian Oil and Gas Association, Forum for diving and subsea intervention. We were asked whether we could provide standardized tables for TUP-diving (transfer under pressure). This has now been included in the draft 6th edition (Rev H).

A table has been inserted to facilitate identification of Nitrox dives profiles that may exceed daily limits or call for two days off diving after a given period of successive days of diving (Rev K).

Emergency decompression procedures

We have suggested a set of emergency decompression procedures for those cases where there is vast omitted decompression - typically situaations where the diving profile is unknown and/or the bottom time exceeds the longest stipulated time in the tables (Rev H). 

Basic Life Supoort (BLS ) Flowchart

Flowchart revised in agreement with European Resuscitation Council 2021 guidelines (Rev H). 

Oxygen Treatment of Non-Diving Related Injuries

The text describing treatment details of Gas gangrena, CO intoxication and osteoradionecrosis has been removed and the reader has been adviced to search other litterature to learn more (Rev I)

Examination checklist

We have made a few changes to this list after valuable feedback from consultans in neurologi Tor-Arne Pisani Valen and Bernd Müller at the unit for hyperbaric medical treatment, Department of Occuptional Medicine,  Haukeland University Hosptial. (Rev J)

Hearing comments

You may download the latest (draft)  6th edition of the NDTT below. You may additionally download the comments we have received and our responses to each and one of them.