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  • Decompression dives

Decompression dives

If you exceed the no-decompression limit on a dive, when NO DEC TIME reaches zero, your dive changes into a decompression dive. Therefore, you must perform one or more decompression stops on your way to the surface.

When the decompression dive starts, the NO DEC TIME on your display is replaced by ASC TIME, and a CEILING indicator appears. An upward pointing arrow also prompts you to start your ascent.

Suunto DX provides the decompression information required for ascent with two key values:

  • CEILING: depth that you should not go above
  • ASC TIME: optimum ascent time in minutes to surface with defined gases

If you exceed the no-decompression limits on a dive, the dive computer provides the decompression information required for ascent along with subsequent details that are updated as you ascend.

In other words, rather than requiring you to make stops at fixed depths, the dive computer lets you decompress within a range of depths. This is known as continuous decompression.

Ceiling, ceiling zone, floor and decompression range

Before you do a decompression dive, you need to understand the meaning of ceiling, ceiling zone, floor, and decompression range. You need to understand these concepts to be able to correctly interpret the guidance provided by the dive computer.

  • The ceiling is the shallowest depth to which you should ascend when doing decompression.
  • The ceiling zone is the optimum decompression depth range. It is the range between the ceiling depth and 1.2 m (4 ft) below that ceiling.
  • The floor is the deepest depth at which the decompression stop time does not increase. Decompression starts when you pass this depth during your ascent.
  • The decompression range is the depth range between the ceiling and floor. Within this range, decompression takes place. However, it is important to remember that the decompression slower at or close to the floor compared to the ceiling zone.

The depth of the ceiling and floor depends on your dive profile. The ceiling depth is fairly shallow when you first enter the decompression dive. But if you remain at depth, the ceiling depth moves downward, and the ascent time increases. The opposite is also true: the floor and ceiling depths may change upwards while you are decompressing.

When conditions are rough, it may be difficult to maintain a constant depth near the surface. In such cases, it is more manageable to maintain a depth somewhat below the ceiling, to ensure that the waves do not lift you above the ceiling. Suunto recommends that you decompress deeper than 4 m (13 ft), even if the indicated ceiling is shallower.

Ascent time

The ascent time shown on your dive computer is the minimum amount of time needed to reach the surface on a decompression dive. This includes:

  • Time required to do deepstops
  • Ascent time from depth at an ascent rate of 10 m (32.8 ft) per minute
  • Time needed for decompression
  • Time needed for extra safety stops if ascending too fast during the dive
WARNING:

Your actual ascent time may be longer than displayed by Suunto DX. It may be longer if your ascending speed is slower than 10 m (32.8 ft) per minute or you are doing a decompression stop deeper than the recommended ceiling. Take this into account, since it might increase the amount of required breathing gas to reach the surface.

Decompression guidance

On a decompression dive, there can be three kinds of stops:

  • Safety stop
  • Deepstop
  • Decompression stop

Though not recommended, you may break (ignore) deepstops and safety stops. Suunto DX penalizes such actions with additional stops or other measures, either during the dive or on following dives. For more information, see Safety stops and deepstops.

Suunto DX shows the ceiling value always from the deepest of these stops. Deepstop and safety stop ceilings are always at constant depth when you are at the stop. Stop time is counted down in minutes and seconds.

With decompression stops, the ceiling is always decreasing while you are near the ceiling depth, providing continuous decompression with optimum ascent time.

NOTE:

It is always recommended to keep close to the decompression ceiling when ascending.

Below the floor

The blinking ASC TIME text and an upward arrow indicate that you are below the floor. A low priority alarm will also sound. You should start your ascent immediately. The ceiling depth is shown on the left side of the center field, and the minimum total ascent time on the right side.

Below is an example of a decompression dive with a ceiling of 3 m and total ascent time of 9 minutes.

below floor

Above the floor

When you ascend above the floor, the ASC TIME text stops blinking and the upward arrow disappears, as shown below.

above floor

This indicates you are in the decompression range. Decompression begins, but slowly. Therefore, you should continue your ascent.

At the ceiling

When you reach the ceiling zone, the display will show you two arrows pointing at each other as shown below.

at ceiling

During the decompression stop, your total ascent time continues to count down towards zero. If the ceiling moves upwards, you can ascend to the new ceiling.

You may surface only after ASC TIME and CEILING have disappeared. This means that the decompression stop and any mandatory safety stop have been completed.

You are advised, however, to stay below the ceiling until the STOP text has also disappeared. This indicates that the three (3) minute recommended safety stop has also been completed.

Above the ceiling

If you ascend above the ceiling during a decompression stop, a downward arrow appears in from of the ceiling depth, and a continuous beeping starts.

above ceiling

In addition, an error warning Er reminds you that you have only three (3) minutes to correct the situation. You must immediately descend to, or below, the ceiling. If you continue to violate the decompression, the dive computer goes into a permanent error mode (Error state (algorithm lock)).

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