How Deep Can You Dive Using Air?
Three factors controlling how deep can you dive using air
There are three factors that determine how deep can you dive using air:
- Inert-Gas narcosis
- CNS oxygen toxicity
- Gas density
Inert-Gas Narcosis
Inert gas narcosis using air begins to become debilitating through an anaesthetic effect below 30m/100ft. This is due to the high lipid solubility of the nitrogen component (79%) in the air. The correlation between the lipid solubility of a gas and its anaesthetic property is defined in the Meyer-Overton Law of Lipid Solubility.
Read more about Narcosis in this article: Nitrogen Narcosis – Perceptions of Susceptibility
CNS Oxygen Toxicity
Divers have to limit their oxygen exposure to a maximum partial pressure of 1.4 ppO2 in order to avoid Central Nervous System (CNS) toxicity. At high pressure, oxygen interferes with neural function and will cause convulsions. This 1.4 ppO2 limit equates to a 56.6m/185ft maximum depth when breathing air (21% O2).
Read more about Oxygen toxicity in this article: Oxygen Exposure Management For Divers
Gas Density
The issue of Gas Density and its role in CO2 retention (hypercapnia) is woefully under-educated by many scuba training agencies. Gas density has been well studied and it is proven that a greater density of breathing gas reduces respiratory efficiency that leads to CO2 retention.
Studies by the US Navy Experimental Dive Unit (NEDU) have illustrated a huge uptake in CO2 retention when breathing gas density exceeds 6g per litre. When breathing air, that 6g/L limit is reached at just 36m/120ft.
To date, most of the major recreational dive agencies have simply ignored those scientific findings. They don’t teach gas density at all, to either instructors or technical divers.
If big agencies DID acknowledge that issue and applied appropriate safety measures, then it’d severely curtail recreational deep diving – and that’d impact industry profits.
There are some (more ethical) agencies that actively teach gas density management – and they apply a 30m/100ft limit to air/nitrox diving. Beyond this, they use helium (trimix) mixtures to mitigate both gas density and inert-gas narcosis risks.
Simon Mitchell, a leading decompression and hyperbaric physics researcher, gives an excellent lecture on gas density in this YouTube video. Every dive instructor and deep diver should watch it…
Nitrogen Narcosis – Perceptions of Susceptibility
The greatest variation between divers is the individual perception of susceptibility to narcosis. This is the person's awareness of when, or if, they are suffering a decline in mental cognizance due to elevated nitrogen partial pressure.
Does Nitrogen Narcosis Impairment Persist?
A new study on nitrogen narcosis challenges the long held presumption that nitrogen narcosis impairment dissipates immediately on ascent from depth.
Nitrogen Narcosis Sedation & Consciousness
The commonly taught model of alcohol-like intoxication fails to describe the nuanced cognitive effect upon the diver and, at worst, promotes divers towards a dangerous misbelief that they aren't mentally impeded by narcosis
About The Author
Andy Davis is a RAID, PADI TecRec, ANDI, BSAC, and SSI-qualified independent technical diving instructor who specializes in teaching sidemount, trimix, and advanced wreck diving courses.
Currently residing in Subic Bay, Philippines; he has amassed more than 10,000 open-circuit and CCR dives over 30 years of diving across the globe.
He has published numerous diving magazine articles, designed courses for dive training agencies, and tests/reviews dive gear for scuba equipment manufacturers. He is currently writing a series of advanced diving books and creating a range of tech diving clothing and accessories.
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.
Originally posted 2019-02-22 12:12:32.