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DM 4. Decompression procedures

The DCIEM (Canadian Defence and Civil Institute for Environmental Medicine) Standard Air Decompression Tables must be used for all Macquarie University diving operations. The full tables can be found in AS/NZS2299.1, Appendix F, Table F1 (A). A short version of the DCIEM tables has been adapted to fit Macquarie University (no-decompression diving only, 30m maximum) and is included in 'diving forms'. A field version of this table is available from the UDO. The DCIEM EANx Tables must be used for all EANx diving operations.

4.1 - Risk factors

The DCIEM tables make specific alterations for situations such as diving at altitude. These procedures must be followed when appropriate. Substantial risk-increasing factors (such as diving in cold water, or doing strenuous work during the dive) should lead to further shortening of dive time. Dive coordinators should make DCIEM table calculations using the next deeper water depth when substantial risk-increasing factors are present (adding 3 metres to the maximum depth for the purposes of table calculations). In cases of multiple substantial risk-increasing factors DCs should consider adding 6 metres to the maximum water depth for the purposes of table calculations.

The UDO may require safety factors such as adding additional depth to the maximum depth for the purposes of table calculations, or limiting the maximum number of ascents per dive or day. For more information on risk factors during diving, please contact the UDO.

4.2 - Repetitive dives

A repetitive dive is any dive conducted within 18 hours of a previous dive, or that has a Repetitive Factor greater than 1.0 when calculated using the DCIEM tables. Repetitive diving is allowed at Macquarie University. A maximum number of dives per day and per diver is indicated in the Fieldwork Notification & Dive Plan and must not be exceeded without prior approval of the UDO.

Procedures for calculating Repetitive Factors and Repetitive Groups are included in AS/NZS2299.1, Appendix F, section F5 (Repetitive Diving) and will be explained to all divers and DCs during the induction process by the UDO. Special care must be taken when calculating repetitive dives to ensure that return groups are properly calculated. Attention is also drawn to maximum repetitive group associated with remote areas (see section 4.4). When diving three times a day or more, divers should have a 24 hour break from diving after three days of diving. When diving once or twice a day, a 24 hours break should be observed after four days of diving.

4.3 - Safety stops

For all single dives deeper than 9 metres and all repetitive dives regardless of depth, divers should perform a safety stop at between 3 to 5 metres depth for 3 to 5 minutes, except where the performance of a safety stop increases risk from other hazards or where the safety stop is deeper than the actual dive.

4.4 - Remote area bottom time and repetitive group adjustments

AS/NZS 2299.1:207 provides limits to bottom times and repetitive group, based on the distance to the nearest recompression chamber and has been approved for use by scientific divers. Transport time must be realistically assessed by the DC based on the most reliably available form of transportation.

Maximum Dive Depth

Maximum Bottom Time, in minutes

 (metres)

Column A

(chamber within 2 hours)

Column B

(chamber further than 2 hours away)

6

480

360

9

240

190

12

150

120

15

75

60

18

50

40

21

35

30

24

25

20

27

20

15

30

15

10


AS2299.1:2007 Table 4.2 also specifies maximum Repetitive Groups limits for repetitive dives, depending on level of recompression chamber support (based on DCIEM air tables).

 

Maximum Dive Depth

Maximum Repetitive Group

(metres)

Column A

(chamber within 2 hours)

Column B

(chamber further than 2 hours away)

6

H

G

9

H

G

12

H

G

15

G

F

18

F

E

21

E

D

24

E

D

27

D

C

30

D

C

 

4.5 - Dive computers

Macquarie University encourages the use of personal dive computers as recorders of dive time and depth only. All dive planning and decompression calculations must be done using the appropriate DCIEM tables. A copy of the DCIEM tables must be present during all dive operations. It is noted that dive computers have various depths cut-offs for counting dive time. It is the responsibility of the surface support personnel to calculate bottom time, based on time leaving surface and time reaching surface, minus any safety stops and ascent time. Dive computer's "bottom time" should not be transferred to the 'Dive Safety Log' without checking that they accurately represent the time from leaving surface to the time starting the final ascent.

Recommendations for dive computer use:

  1. Where a computer has the ability to do so, it should be adjusted to the setting most similar to the relevant DCIEM tables;
  2. Where a diver is using a dive computer as well as DCIEM dive tables, the DCIEM tables are expected to be more conservative. However, the advice of the more conservative of the two must always be followed;
  3. A diver should not begin using a dive computer if they have had an exposure to ambient pressures of greater than 1 ATA during the previous 24 hours unless the computer was also exposed at the same time, to the same pressure (i.e. it was being worn at the time);
  4. Computers should not be shared between divers;
  5. DCIEM ascent rates rules (15-18 meters/min) must still be followed; and
  6. DCIEM safety stop rules must still be followed.

 

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