Safety Talk This Month
Ascent's a critical phase
In browsing through the Annual NDC Diving Incidents Report it was very clear that ascent related incidents are a significant factor in many incidents, including DCI and a number of the fatalities.
It strikes me that the ascent is probably the most critical phase of the dive. It is essential to ascend because we can’t survive, long term, under the water. You don’t HAVE to continue a descent, you don’t HAVE to continue the bottom phase of a dive, however you do have to ascend.
Even more importantly you have to do so safely.
At the start of a dive a direct ascent is easily possible. With a low nitrogen loading you might even get away with a faster than normal ascent but it is still not advisable. However, as the dive progresses the risks associated with a fast ascent increase significantly and as time passes a direct ascent to the surface without decompression stops becomes impossible to do safely. As depths increase, the time you have available before getting into this situation becomes shorter and more critical.
One of the incidents in the 2010 report involved a rapid ascent from a depth of 60m after a 20 minute dive. The consequences? They may well have been predictable, they were certainly tragic. Proper consideration and preparation for this critical phase of the dive is essential.
Jeff Reed, BSAC National Diving Officer
Most important phase
Ascend to the surface and life becomes so much easier. There is lots of gas to breathe, there is the chance to get out of the water onto a secure platform and, if necessary, there is access to support and medical care (eg first aid oxygen, AED and evacuation to hospital or chamber). Even though DCI can be potentially treated, it is still better to conduct any required decompression stops but then again we can’t yet breathe water.
Loss of buoyancy control is still a significant factor in ascent related incidents. For the inexperienced diver there can be little substitute for continual practice. As divers gain experience, one of the triggers in loss of buoyancy control seems to be associated with ascents without a visual reference point (shotline or seabed) and again supervised practice can help but such practice should encourage the use and practice of the reference points all divers carry with them (depth gauge or computer) and how to monitor them properly. Watching just for a consistent change in numbers can, and has, resulted in divers happily thinking they were ascending at a steady rate when they were actually descending.
Even for experienced divers loss of buoyancy control can sometimes occur although it is normally through events such as sticking inflation valves or loss of weights. Simple equipment maintenance can often prevent rather than cure this.
The deployment of DSMBs is frequently implicated in ascent problems including entanglement, snagging, excessive buoyancy or sometimes simply ‘task loading’. Task Loading not only overwhelms the ability of a diver to cope, it frequently has a knock on effect on our buoyancy. Whilst trying to deal with the complexities of multiple simultaneous demands we have a tendency to subconsciously hold our breath. While maintaining depth this is not a significant problem. However, during an ascent not only does it increase our buoyancy, the expanding gas provides further increases in buoyancy and risks lung damage from over expansion with the inherent consequences. The answers include, practice, buddy support and breathing awareness.
Breathing normally at all times is remains the best advice. However, being conscious of our breathing in an ascent situation can help protect us. Rapid breathing shouldn’t be a problem in this context but being aware of any breath holding and consciously overriding it may protect us and avoid overexpansion injury. In excessively fast ascents you may need to breathe out continuously.
Think SAFE – Dive SAFE
BSAC Safety and Development manager
Please enter your text here