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Scuba Q&A: Scuba Diving Anxiety & CO2 Narcosis

Scuba diving anxiety effects many divers. It can be anticipated with beginners, but even very experienced divers can be blindsided by sudden and unexpected anxiety on deeper dives. What causes it?

QUESTION:  I have a lot of anxiety descending…any tips, suggestions or tricks??  I struggle with lots of anxiety when in deep rough water and descending.

ANSWER: This experience sounds entirely descriptive of CO2 retention (hypercapnia) and resulting CO2 narcosis.

You will produce additional CO2 as a result of exertion – which is common in novice divers who typcially have less efficient diving skills.

Scuba diving anxiety is commonly a product of hypercapnia

The retention of CO2 is exagerated if your breathing becomes shallow and rapid. Scuba diving equipment further exagerates CO2 retention because it adds additional dead air space to the respiratory tract.

As you descend, the increasing ambient pressure has a direct effect; elevating CO2 partial pressure inside the body (Dalton’s Law).

See: How deep can you dive using air?

If your dive is moderately deep (30m/100ft+), then increasing gas density in your lungs further contributes to CO2 retention via changing respiratory gas/fluid dynamics that reduces your lungs ability to expel CO2.

Be aware of gas density recommendations

Divers Alert Network (DAN) has issued recommendations on maximum gas density when scuba diving.  Thhe scientifically proven maximum gas density of 5.2g/l actually sets a max recommended depth for diving air (21%) at 31m/102ft.  The limit for EANX3 works out slightly deeper at 33.5m/110ft.

CO2 is a very narcotic gas

CO2 is a highly narcotic gas; 25x more narcosis effect than nitrogen. So any CO2 retention has an immediate cognitive impact.

The cognitive impact of CO2 narcosis initially presents as a strong sensation of unease and develops to acute panic as severity rises. Your capacity for deliberate, rational judgement diminishes rapidly – although you won’t percieve that degredation in thinking ability. There is also a sensation that you “can’t get enough breath”, no matter how hard you breath.

CO2 narcosis presents as scuba diving anxiety

CO2 narcosis is nicknamed “dark narc” for that reason. With experience, CO2 narcosis is very discernable from nitrogen narcosis. This is very common in novice divers and, contrary to some suggestions in this thread, it is entirely a physiological, NOT psychological event (i.e. not underlying anxiety).

The best response to scuba diving anxiety

If you experience CO2 narcosis, the best response is:

1.     Stop all exertion and focus on deep, lung-flushing, breathing.

2.     Mentally resist the rising stimulation to panic. Panic response will decrease breathing efficiency and raise exertion. It will also lead to flawed judgements and dangerous instinctive responses.

3.     Ascend to a shallower depth, as this will directly lower venous ppCO2 and reduce breathing gas density.

3.     CO2 narcosis dissipates quite rapidly (within minutes) if you take appropriate actions.


About the Author

andy davis technical diving philippines

Andy Davis is a RAID, PADI TecRec, ANDI, BSAC and SSI qualified independent technical diving instructor who specializes in teaching advanced sidemount, trimix and wreck exploration diving courses across South East Asia.  Currently residing in ‘wreck diving heaven’ at Subic Bay, Philippines, he has amassed more than 9000 open circuit and CCR dives over 27 years of diving across the globe.

Andy has published many magazine articles on technical diving, has written course materials for dive training agency syllabus, tests and reviews diving gear for major manufacturers and consults with the Philippines Underwater Archaeology Society.

He is currently writing a series of books to be published on advanced diving topics.  Prior to becoming a professional technical diving educator in 2006, Andy was a commissioned officer in the Royal Air Force and has served in Iraq, Afghanistan, Belize and Cyprus.

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