Avoiding DCI (or how not to spend the week in the pot’)
Thought it was time to delve back into the archives and see what was being cirulated by members. This is a a short run down on DCI (Decompression Illness) and how to avoid it. This is from Gareth back in 2005 so not too long ago.
By Gareth Leyshon
I have the reputation for being ‘the nutter who does that deep diving’ & worse still ‘the nutter who decompresses for hours after a dive’. Contrary to popular belief, I am not ‘a nutter’; I certainly don’t want to get a ‘hit’ (decompression illness).
We should all understand that any dive carries the risk of DCI, even if you do everything properly.
To safeguard myself I dive defensively, i.e. I try to do things prior, during & after the dive that reduce the risk of a ‘hit’ – this doesn’t guarantee that you will get a hit, it just helps the odds!
Here are a few pointers, & explanations.
If you want more information I would recommend reading the Decompression Matrix by Bob Cole.
1. Be Well Hydrated
• Avoid drinking Alcohol prior & after diving. Alcohol will cause significant dehydrate & reduce blood surface tension (making it easier for bubbles to form).
• Drink ‘still’ fluids prior too & after diving. (On extended decompression consider drinking during the decompression stop phase of the dive).
• Do not drink diuretics such as Tea & Coffee, these increase dehydration. (Note some fruit juices are diuretic.)
• Drink steadily during the day; do not stop drinking in an effort to avoid peeing when in a drysuit.
2. Pre & Post Dive Exercise
• Keep exercise to a minimum both before & after the dive. Exercise prior to the dive increases the generation of bubble nuclei. Post dive exercise increases the potential for micro-bubbles to form DCI bubbles.
• Make use of lifts on boats to minimise work when returning to the boat.
• De kit in the water & share the weight when recovering kit into the boat.
• Ensure divers can sit as near to the ladder to de-kit as soon as possible.
3. Dive Profile
• Avoid Saw tooth profiles – ascents create bubbles, descents compress bubbles & allow them to shunt through the lung filter, swim around objects rather than over them. – Add additional safety stops if you have had a saw tooth profile.
• Yo-Yo profiles are even worse. Multiple returns to the surface & immediate descents are exceptionally hazardous. Ideally avoid re-descent & have a good surface interval. In the event that a descent is required ascend slowly with additional safety stops. If possible breath a gas with minimal Nitrogen content (Nitrox) whilst using an air table.
• The most important section of the dive.
• Ascend steadily at a controlled rate.
• The dive rate must not exceed your table requirements.
• Slow the ascent rate in the last 6m.
• Plan to stop at 6m & 3m to check the dive plan / decompression obligations.
• Add a safety stop at 3m if possible or 6m if surface conditions do not permit it.
• Avoid having to re-descend.
• If the ascent is not controlled add additional safety stops at 6m & 3m.
• DO NOT re-descend on reaching the surface if decompression stops have been missed – advise the dive marshal, consider using Oxygen, ensure you are monitored for signs of DCI.
• Always attempt to ascend up a reference point, cliff, shot-line, anchor-line or SMB line.
• Practice ascending without a reference point once you have mastered ascents on a cliff face or up a shot line (well inside the no-stop limit).
5. Be thermally comfortable before & after diving.
• Keep divers cool (not cold) prior to the dive, this reduces dehydration & perspiration that may rapidly cool a diver once he enters the water.
• Keep warm (not hot) after the dive to ensure steady effective off gassing.
6. No-Stop Diving
• Do not dive to the edge of the No-Stop limits, this is aggressive diving.
• Stop at 6 or 3m for a short period at the end of each dive regardless of the fact it is a no-stop dive.
7. Repetitive Dive Profiles
• Do not bounce dive shortly after surfacing, this significantly increases the risk of neurological DCI. The micro bubbles compress on descent, cross the lung filter to the arterial circulation. This significantly increases the risk of bubble growth in the arterial circulation.
• Ensure sufficient surface interval between dives. A minimum of 2 hours.
• In the case of deep dives with long decompression periods, it is advised that only 1 dive a day should be undertaken.
8. Avoid hot showers & sun bathing directly after diving
• If the blood temperature is raised significantly (hot showers, sun bathing) the blood surface tension is reduce promoting rapid off gassing, significantly increasing the risk of DCI.
9. Sea Sickness
• Many people dive who suffer from sea sickness, once in the water the sea sickness stops.
• Remember that sea sickness increases your dehydration & increases mental & physical fatigue
• Add conservatism to the dive profile to offset these effects.
10. Diving after a cold
• Mucus can be present not only in the airspace’s of the scull & Eustachian tube’s, causing difficulties with ear clearing on descent & the risk of reverse ear on ascent. But also in the lungs effecting lung efficiency & the risk of trapping air between the mucus & lung lining.
• The RN recommends a 10-day break between the end of a cold & resumption of diving.
• At the very least ascents should be slow with additional safety stops.
11. Diving after injury
• DCI has a high tendency to occur where old or new injuries have occurred. This is due to the fact that the circulation around an injury is often poor.
• It is strongly recommended to dive conservatively after any injury, additional decompression or the use of Nitrox will reduce the risk of DCI.
12. Diving when using medication
• It is strongly recommended that divers should not dive with medication in their system.
• Solubility of gases & other materials is increased under pressure (Nitrogen), the same effect occurs with many drugs which are designed to dissolve progressively into the system through the stomach wall.
• In addition to this fact the Narcotic effect may increase significantly with pressure (i.e. like Nitrogen Narcosis)
• Prior to using drugs whilst diving the advice of a diving doctor should be sought.
• The Dive Marshal must be advised, in the event of a diving injury this information may be important & effect the treatment & or symptoms.
• This ignores the fact that the drug may impair reasoning!
13. Modify your dive in adverse conditions
• When Cold the circulation is reduced to the extremities, this reduces blood flow & therefore off-gassing on ascent. Add additional decompression time to the profile &/or stay well inside the no-stop limits.
• If you have been working hard, or under physical or mental stress, add additional decompression time to the profile. Increased consumption of gas means increased absorption of the inert gas (Nitrogen), give time for this to be released from the body.
• If you feel that you, your profile, or the conditions under which the dive has occurred are more extreme than usual, then it is advisable to add a degree of conservatism to the dive profile, i.e. additional decompression.
14. Understand your decompression model
• Don’t just follow your computer or table blindly.
• Use a working decompression model you trust – compare new tables or computers to your trusted model.
• Should a new table or computer gets you out of the water earlier – ask WHY? & is it SAFE?
• Understand how & what the safety factors are doing that you can add or switch on.
• Run comparative test exercises between the table you trust & the new one. Diving defensively (or adding conservatism to your diving)This does not necessarily mean only shallow diving, no decompression or no adventurous diving. This means taking a defensive approach to decompressing. This can be; • Using a lesser table than that allowed i.e. Table B instead of table A.
• Setting the personal preference of the dive computer back from P0 to P1 (Sunnto), or setting the altitude setting A1 instead of A0.
• Breathing a gas with less Nitrogen than that used by the table or computer i.e. Nitrox 32 on an air table.
• Adding additional in water decompression at the end of the dive (ensure this is added to the 1st dive profile prior to planning the next dive).
• Keep the ‘work’ to the minimum during the dive.
• Increase decompression time if you have been working hard.
The consequences of not following this advice can be clearly seen in this article written by an Instructor.
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