SCUBA DIVING UNIVERSITY / SAFETY
Oxygen, narcosis & breathing gases
Separate the effects of oxygen, nitrogen and carbon dioxide. Learn why gas selection, analysis and breathing workload belong in the same conversation.
10 lessons in this section
YouDive educational guide · References checked 30 September 2026 · Independent instructor and medical review pending. This library does not provide certification, individual medical clearance or a dive plan.
Oxygen toxicity explained
Oxygen is essential for life, but too much exposure under pressure can injure the body.
Read the guide →02Understanding partial pressure
A gas mixture has the same percentage in the cylinder while its partial pressures change with depth.
Read the guide →03Nitrox benefits and limits
Nitrox changes the balance of oxygen and nitrogen; it does not make every dive safer or allow unlimited depth.
Read the guide →04Maximum operating depth is a boundary
A gas’s maximum operating depth is a planning limit, not a target to reach.
Read the guide →05Nitrogen narcosis and judgement
Narcosis can impair thinking and coordination at depth, including the judgement needed to recognise impairment.
Read the guide →06Carbon dioxide retention
Breathing difficulty and excessive workload underwater deserve an early response.
Read the guide →07Gas density and work of breathing
Depth changes how demanding it can be to move breathing gas through the system.
Read the guide →08Hypoxia and inadequate oxygen
Too little oxygen can cause loss of consciousness, potentially without a useful warning.
Read the guide →09Contaminated breathing gas
Breathing gas quality is a safety issue even when the cylinder pressure looks correct.
Read the guide →10Gas analysis and identification
The cylinder you intend to breathe must match the gas you have planned for.
Read the guide →