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NHS treatment, decompression sickness symptoms, Poole and Reading


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Risk factors

Ascents | Bottom Times |
Environmental Conditions | The Individual | Medical | Summary

Divers control the risk factors inherent in scuba diving by regulating such things as ascents, bottom times, breathing mixes, decompression schedules and also take into account environmental conditions, hydration and personal health.


Any dive performed where compressed gas is breathed requires the ascent to surface to be carried out in a controlled manner, allowing dissolved gases to be diffused safely via the lungs (the effect of Henry's Law) and avoiding over-expansion of the lungs (the effect of Boyle's Law).

Training organisations recommend different ascent rates, typically from 6 to 18 metres a minute. Dive computers often vary recommended ascent rates according to the dive profile and the current depth. Some divers follow their smallest bubbles to gauge the ascent rate.

Whichever method is used, the final 10 metres to surface is crucial - due to the pressure halving and volume increasing by a factor of 2. An uncontrolled ascent in this range is likely to cause problems if:



As with ascent rates, many different recommended dive tables and decompression algorithms are in use. Originally the timings were developed by observing people working under pressure. Later changes were made based upon experimentation and theories based on gas exchange in the body.

Whether a table or computer is used, the decompression schedule is designed to allow the diver to control decompression. Greater dive depths and longer bottom times increase gas loading, requiring longer decompression and increasing risk. Not exceeding bottom times is essential.



In the UK the environmental conditions are a significant factor, even in the summer months.

It is important to get an accurate weather forecast before the dive to assess the likely conditions. Choppy sea states can affect some and sea sickness can lead to dehydration, increasing the risk of decompression illness.

Poor underwater visibility is not unusual, particularly if silt is disturbed. Disorientation and confusion in such conditions can happen very quickly. Cold conditions can affect co-ordination and impair operation of equipment. Fog presents an additional hazard, hindering diver recovery and the ability of the emergency services to assist in the event of an incident.

Tidal conditions can cause real difficulty in completing decompression schedules safely.

All of the above conditions have contributed to divers requiring recompression treatment.



Sea-sickness, dehydration and fatigue are contributory factors in the risk of decompression illness.

Each individual's circumstances and fitness to dive should be taken into account when planning a dive.



Medical issues can play a big part in the increased risk of decompression illness, such as:

For more information about these and other medical issues can be found in our medical faq section.



Our records at The Diver Clinic show that these risk factors have contributed to many divers requiring recompression treatment.




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