Whether you’re a novice or a pro scuba diver, you may be wondering if it’s possible to dive with pure oxygen. Many divers are curious if filling tanks with 100% O2 would allow for unlimited underwater breathing and bottom time.
While this seems appealing in theory, recreational scuba diving with pure oxygen is extremely dangerous in reality. Breathing pure O2 underwater can quickly cause deadly oxygen toxicity seizures and blackouts.
This comprehensive guide examines the risks of diving with pure oxygen in detail.
- How oxygen toxicity happens and its effects
- The safe oxygen exposure limits when diving
- Dangers of oxygen toxicity at various depths
- The equipment and training needed for enriched air nitrox diving
- Rules prohibiting pure oxygen from all scuba training agencies
- Safer alternatives like nitrox blends
- Step-by-step ways to maximize oxygen safety when scuba diving
Let’s thoroughly analyze the science and safety considerations of breathing pure oxygen underwater.
Why Breathing Pure Oxygen Underwater Is Deadly
Before examining the specifics of oxygen toxicity, it’s important to understand why pure oxygen is so risky when scuba diving.
Here are the key reasons:
Increased Oxygen Partial Pressures
The deeper you dive underwater, the higher the ambient water pressure becomes. This pressure exerts a force on your lungs and breathing gas. At 20 feet / 6 meters underwater, the pressure is 3 times higher than at the surface.
This increased pressure compresses any breathing gas in your scuba tank. Inhaling compressed oxygen at depth results in higher oxygen partial pressures in your lungs and bloodstream.
Your body can safely tolerate low pressures of oxygen found in regular air at sea level. But it cannot handle the multiplied oxygen pressures of pure 100% O2 when breathing compressed gas underwater.
No Inert Nitrogen to Balance Oxygen
Standard compressed air is only 21% oxygen; most (79%) is inert nitrogen gas. This nitrogen acts as a buffer, diluting the oxygen. It prevents oxygen partial pressures from becoming toxic when compressed at depth.
Pure oxygen has no balancing nitrogen to offset the high oxygen percentages now pressurized. This makes pure O2 extremely dangerous for scuba diving.
Modern Scuba Gear is Not Designed for Pure O2
All recreational scuba equipment like regulators, tanks, and compressors are engineered for breathing compressed air, not pure oxygen. The fire and detonation risks of high-pressure O2 can cause catastrophic equipment failures.
Using pure oxygen violates training agency safety standards and may result in certification loss. Only technical divers use pure O2, with specialized gear and training.
Now let’s analyze how oxygen causes toxicity symptoms and convulsions when diving.
How Oxygen Toxicity Occurs When Scuba Diving
Oxygen toxicity manifests in two major forms when scuba diving: central nervous system (CNS) toxicity and pulmonary toxicity.
Let’s examine how each happens.
Central Nervous System Oxygen Toxicity
CNS oxygen toxicity stems from oxygen pressures making dissolved O2 in the blood overly saturate nerve tissues. This over-saturation creates free radicals that damage neurons, especially in the brain and spinal cord.
Damaging effects escalate rapidly, with little warning. Vision starts narrowing as a first sign.
Pulmonary Oxygen Toxicity
Prolonged exposure to increased oxygen pressures can also harm lung tissues. Fluid begins building up in lung air sacs, causing burning chest pain and shortness of breath.
This pulmonary toxicity is rarer in divers than CNS effects. But severe cases can cause permanent lung damage and respiratory impairment.
Signs and Symptoms of Oxygen Toxicity
Being able to recognize oxygen toxicity signs is critical for all scuba divers. Here are the symptoms in order of escalating severity:
- Tunnel vision with narrowed visual field
- Tingling sensations in extremities
- Nausea and dizziness
- Mild disorientation and confusion
- Increased breathing rate
- Burning chest pain when breathing deeply
- Severe nausea and vomiting
- Muscle twitching, especially around the mouth and face
- difficulty breathing and chest tightness
- Headaches, fatigue, anxiety
- Severe dizziness/vertigo
- Intermittent vision blackouts
- Uncontrollable muscle spasms and convulsions
- Complete vision loss
- Auditory disturbances and ringing
- Loss of consciousness
Oxygen toxicity can rapidly progress from mild to convulsions and blackouts in just 1-2 minutes. Immediately ascend if any moderate symptoms appear underwater.
Oxygen Toxicity Depths When Scuba Diving
At what depths and partial pressures does oxygen become toxic when breathing it underwater?
Here are the exposure limits:
- 20 feet / 6 meters – Mild symptoms first noticed
- 30-50 feet / 9-15 meters – Moderate symptoms and toxicity risks
- 66 feet / 20 meters – Central nervous system (CNS) oxygen toxicity likely
- 100 feet / 30 meters – CNS oxygen toxicity is almost certain, leading to convulsions
- 130 feet / 40 meters – Maximum recommended depth due to high risk of seizures
These limits apply when breathing standard compressed air (~21% O2). With 100% oxygen, toxicity happens much shallower. Recreational dives should not exceed 130 feet, even with compressed air.
Note these additional factors also increase oxygen toxicity susceptibility:
- Cold water temperatures
- Overexertion when diving
- Back-to-back repetitive dives
Proper training, gas management, dive planning, and conservatism allow divers to manage oxygen exposure while mitigating toxicity risks.
Analyzing Recreational Scuba Gear & Gas Blends
Since pure oxygen is so dangerous for scuba diving, what options exist for safer gas blends and gear?
Compressed Air: The Beginner Standard
All entry-level recreational scuba training is conducted by breathing compressed air:
- Contains ~21% oxygen
- ~79% nitrogen balance
- Pressurized to fill scuba cylinders
Compressed air is relatively safe for conservatively planned dives up to 130 feet maximum. It allows ample bottom time with minimal oxygen toxicity risk and nitrogen narcosis effects.
Scuba gear like regulators and tanks are designed and serviced to handle compressed air fills. Using pure oxygen risks explosions from higher pressures.
Nitrox: Enriched Oxygen Blends for Advanced Divers
While 100% oxygen is prohibited, nitrox-enriched air blends offer an advanced alternative:
- Contains 32-40% oxygen
- Reduced nitrogen levels (60-68%)
- Allows longer bottom times and shorter surface intervals
- Enables deeper “equivalent air depth” dives
- Requires additional nitrox training and certification
- Needs oxygen analyzers to verify blend percentages before every dive
- Has maximum operating depth (MOD) limits
Nitrox-like 32% and 36% EANx mixes can be safer when properly mixed, analyzed, and managed. But additional training and gear considerations exist when increasing oxygen exposure.
Pure Oxygen: Technical Diving Only
Technical divers sometimes use pure oxygen underwater, but only with the following:
- Extensive additional training (Tec, Cave, CCR)
- Special regulators, tanks, and rebreathers designed for pure O2
- Strict depth limits (usually only final 20-foot decompression ceiling)
- No-decompression open-water scuba dives should never use pure oxygen
Even technical divers avoid breathing 100% O2 for long durations at depths below 20 feet. It simply risks toxicity.
Rules & Guidelines for Oxygen Exposure Limits When Diving
To maximize safety, all major recreational scuba training agencies globally forbid pure oxygen use by beginner divers.
- 100% oxygen prohibited for recreational diving
- Maximum 40% oxygen blend for enriched air nitrox
- Nitrox course required to use EANx mixes
- 100% oxygen exposure in diving discouraged
- Maximum oxygen exposure of 1.4 ATA oxygen partial pressure
- Maximum equivalent air depth 130 feet on compressed air
- 100% oxygen exposure is prohibited under any situations
- Maximum 36% oxygen content for recreational nitrox diving
- Additional nitrox certification required
Violating these standards puts your credentials and safety at risk. Never attempt to source or fill scuba cylinders with pure oxygen. Leave 100% O2 diving only to highly trained technical divers.
6 Steps to Safely Optimizing Oxygen Exposure When Scuba Diving
While pure oxygen diving is extremely dangerous, you can take steps to maximize oxygen intake while staying safe.
Get nitrox certified to legally use enriched air blends with 32-40% oxygen. This allows longer bottom times while controlling depth based on the gas mix.
Start conservatively with EAN32 (32% oxygen) to limit oxygen toxicity buildup when first starting nitrox diving.
Use oxygen analyzers to verify tank oxygen percentages before every nitrox dive. Know your maximum operating depth (MOD) for that specific blend.
Extend surface intervals between repetitive dives to 100 minutes minimum. This eliminates residual nitrogen and oxygen loading from previous dives.
Stay hydrated and get adequate, restful sleep between dive days. Avoiding dehydration and fatigue reduces oxygen toxicity risks.
Always make safety stops between 15-20 feet for 3-5 minutes on all dives – even no decompression dives. Slowly ascending the last 20 feet reduces oxygen toxicity after long exposures.
Sticking to these steps lets you maximize bottom time and oxygen exposure while safely staying within training limits.
Recreational scuba diving with pure 100% oxygen is extremely dangerous. The risk of sudden convulsions and blackouts due to oxygen toxicity is too high, leading to drownings.
Stick within recreational depth limits on compressed or enriched air nitrox blends after proper training. Analyze gas mixes to confirm percentages and take steps to extend bottom time while managing oxygen exposure.
Understand the science of oxygen toxicity, how it damages nerves and lungs, and its warning signs. Always dive conservatively within training limits. While 100% oxygen may seem like unlimited breathing underwater, the deadly risks far outweigh any potential benefits for beginners.