5th Ed

The revision process - 5th edition 

There were two main reasons for a new revision of the NDTT in 2019:

  • Inaccuracies and errors reported in the fourth edition should be updated
  • Changes in Norwegian legislation for inshore diving should be incorporated

The errors identified in the fourth edition have been comparatively few and small. However, the Norwegian Labour Inspection Authority has changed regulations for inshore diving which significantly has affected decompression procedures. Most importantly, bottom time restrictions - identical to UK and NORSOK - has been enforced. Secondly, the regulations have specified requirements for multilevel diving.

A summary of changes may be read below. A hearing was completed June 30th.  All feedback has been reviewed and the editors have summarized their responses in this document (Norwegian lanugage only).


Changes and comments

About this website

This website is edited by Jan Risberg (principal author of NDTT 4th edition). It is constructed to be a link between the authors and readers of these tables. Corrections and comments to the tables will be formalized through publication of new revisions. In the time period preceding a revision, there will be discussion between the editors as well as professionals. This website will present suggestions for table changes. We sincerely appreciate comments to the tables: supportive, improvement proposals, inaccuracies a.s.o. Please send us an  e-mail to allow us to follow up!

Topics discussed on this particular page of the website has not been approved/formalized and is not intended to replace recommendations of the last official edition of the table.The revision proposals available for download at the right hand panel, should not be used operationally.

Edition 5 is expected published during spring 2019

We are currently in process of finalizing Ed 5 of the tables. Our temporary/working document can be downloaded here. Please contact us if you have suggestions for improvement.

Changes implemented after the hearing document was distributed have been identified by yellow colour.

Areas subject to revision or correction

Diving at Altitude above 250 m

The text describe limitations for travel to altitudes before diving and how to calculate decompression when diving at altitude. The tables do not satisfactory describe limitations for returning to sea level after a dive at altitude (typically With helicopter) or driving over a mountain area after diving at altitude. A possible solution has been presented in Rev A0

Flying after diving

It is emphasized that the highest repetitive dive group the past 24h should determine minimum surface time before flying (Rev A0).

Standard Air Decompression Table

A request for listing of repetitive groups for bottoms time 5 min has been received. This is relevant for multilevel-dives. In rev A0 such groups have been identified for 5 min bottom time for table Depths 36, 39 and 42m.

A "non" diving day (Serial 18)  has been defined as as a surface interval of minimum 24 (Rev A9). There has been inconsistencies regarding maximum depth (6m or 9m) of "unlimited number" of repetitive dives (Serial 13 and 17, page 7), This has been corrected in Rev A11.

Multilevel diving

A method for using dive computers as an additional safety equipment when diving according to multilevel tables has been described (Rev A10). The requlatory requirements for such diving has been detailed (Rev A15)

Petroleum related diving

Norsok U-103 provide specific guidance for decompression planning of inshore, Nitrox diving. We have described this in some further detail (Rev A12). An earlier provision in NORSOK U-103 2014 ed) stipulated extended decompression time for Nitrox diing with bottom times exceeding that allowed at the actual diving depth. This particular provision has been removed in the 2019 edition and the text modified accordingly (Rev 18).


The example (Serial 4) was not appropriately designed with respect to diving depth causing pO2 to be excessively high. The depth has been changed to avoid this concern (Rev A5)


A question has been raised regarding the consequences of undertaking a dive to depths not exceeding 6m after a SurD-O2 dive. How should this affect the required minimum surface interval for the following SurD-O2 dive. In rev A0 it is suggested that the surface interval should be extended by the dive time of the preceeding shallow dive.

We have received feedback that some DDC are unable to decompress 10 m/min from 15 to 12 m. Section 8 has been rewritten to underscore that this rate (10 m/min) is the optimal rate, but a lower rate is acceptable. (Rev A4)

The procedure for handling oxygen convulsions has been slightly modified (Rev A10 and 21).

The example for SurD-O2 dive has been adjusted according to the bottom time limitations stiuplated by the Norwegian labour Inspection Auhority (Rev A10).

The 45 msw/25 min profile inaccurately described a 4 min stop at 12 msw in Ed 4 of NDTT. This has been corrected  in Ed 5 (printing error in English version of NDTT only).

Page 62: "Total decompression time" has been misprinted for bottom times 70 and 80 min, should read 107 and 133 min. However, decompression stops and Oxygen breathing time is correctly stipulated. There are a few rounding errors (1 min) of listed total decompression times for  some other Depth/bottom time combinations, but these do not affect decompression stipulations (water stops, Chamber oxygen breathing time). (Rev A7)

Page 64: The SurD-O2 table for 51m profile was printed inaccurately because the Depth of decompression stops were not identified. These should be 21, 18, 15 and 12m. The graphic layout has been modified to correct this ambiguity

Prevention of decompression illness

There may be situations in which extension of decompression, to accommodate for individual risk factors, may incur decompression according to a tabulated bottom time indicated as exceptional. There is, however, no need to shorten the actual bottom time to avoid this. (Correction suggested in Rev A3)

Procedures in the event of omitted decompression or uncontrolled ascent

The title was incorrectly and inconsistently translated from the Norwegian original text and has been changed. (Rev A6)

Emergency procedures

There are inconsistencies between the text and the flowchart. The recommendation for oxygen use is probably excessive. Rev A0 suggest simplifications. Further modifications and adjustments have been included in Rev A10.


A new form/checklist ("Summary - Dive and development of symptoms") has been included in Rev A15.

Draft versions

Draft NDTT Ed 5