Recognize the signs of oxygen toxicity: muscle twitching, nausea, dizziness, confusion, and convulsions.

What are symptoms of oxygen poisoning?

• A. Muscle twitching, nausea, dizziness, confusion, convulsions
• B. Bloody tears and fever
• C. Severe headaches and fatigue
• D. Shortness of breath and chest pain

Answer: (A)

Oxygen poisoning, also known as oxygen toxicity, primarily occurs when a person is exposed to high concentrations of oxygen for extended periods, particularly under increased pressure, such as during diving activities. The symptoms listed are classic signs of this condition and stem from the toxic effects of oxygen on the central nervous system. Muscle twitching and convulsions arise due to the heightened excitability of nerve cells when exposed to oxygen at excessive levels. Nausea and dizziness are common as well, as the body struggles to maintain balance and manage the effects of heightened oxygen levels on metabolism and nerve function. Confusion can result from disruptions in brain activity due to oxygen toxicity, further highlighting the neurological impact of oxygen in such scenarios. While the other options describe various health issues, they do not align with the typical symptoms associated with oxygen toxicity. Understanding these symptoms is crucial for divers, as recognizing the signs early can lead to timely interventions and prevention of more severe complications.

Oxygen Poisoning: The Signs Every Open Water Diver Should Know

In the world beneath the surface, oxygen is a trusted ally. It fuels your lungs, powers your brain, and helps you stay alert as you navigate the blue. But when oxygen levels get too high, especially under pressure, the body can react in surprising and dangerous ways. This is oxygen toxicity, sometimes called oxygen poisoning. It isn’t a mythical menace; it’s a real risk that can show up in the gear bag a diver relies on every time they plan a gas mix and a depth.

Let me explain the core idea first. When divers use enriched air (think nitrox) or other oxygen-rich gas blends, the partial pressure of oxygen (PO2) can rise to levels that the nervous system simply cannot handle for extended periods. The brain and nerves get overstimulated, and that’s when symptoms begin to appear. These aren’t warnings you can ignore—ignoring them can lead to serious, even life-threatening events, which is why understanding the signs is more than a study topic; it’s a safety habit.

The classic signs you should know

Among the possible effects, one set of symptoms stands out as the telltale sign of central nervous system (CNS) oxygen toxicity. When exposure climbs too high, you may notice:

• Muscle twitching

• Nausea

• Dizziness

• Confusion

• Convulsions

That exact lineup is what researchers and instructors emphasize because it reflects the brain’s hiperexcitability under excessive oxygen. It’s not a random coincidence—the nervous system gets overstimulated by oxygen at elevated levels, and those five indicators are the red flags.

Why these particular symptoms show up

Think of the brain as a highly sensitive network of wires. Oxygen is essential, but too much of a good thing speeds up the signals in ways that can short-circuit the system. Muscle twitching is often one of the first noticeable effects, a hint that the nerves are firing more vigorously than they should. Nausea and dizziness creep in as metabolism and brain function struggle to find balance. Confusion is the deeper disruption—short-term memory, judgment, and coordination can waver. And then, if the exposure continues, convulsions can occur as the nervous system slips into a dangerous state.

It’s worth noting that oxygen toxicity is not a one-size-fits-all issue. The CNS signs tend to appear with relatively shorter exposure to high oxygen levels, while longer exposures can bring different problems as well. That complexity is why gas planning and depth limits exist in the first place: a little planning can keep the CNS effects well off your horizon.

What this means for divers in the real world

If you’re wearing a nitrox mix or any gas blend that’s higher in oxygen than ambient air, you’re in a regime where CNS toxicity is possible under the right conditions. The speed at which symptoms appear depends on several factors, including:

• The exact O2 percentage in the gas

• The depth you’re at (which changes the PO2)

• The duration you stay in that environment

• Your individual response to oxygen at high levels

Because of these variables, it’s not enough to know “the right gas” in a vacuum. You need to know how long you’ll be at certain depths with that gas and how to monitor your exposure. This is where modern dive computers, gas-measuring tools, and careful planning come into play in the practical world of diving.

A quick note on other symptoms you might hear about

Some people report tingling, tunnel vision, or headaches with oxygen exposure, but the set of symptoms most reliably associated with CNS oxygen toxicity remains the five you’ve read about: muscle twitching, nausea, dizziness, confusion, and convulsions. If you or your buddy notices these signs, treat them as a red flag and reassess your gas strategy and depth immediately.

What to do if signs appear

Safety is the core of the sport, and oxygen toxicity is a moment when fast, calm action matters most. If symptoms show up:

• Stop breathing the high-oxygen mix if you can do so safely. Switch to a gas with a lower oxygen content or to ambient air if that’s feasible without compromising nitrogen balance and depth limits.

• Ascend to a shallower depth to reduce the PO2. Do this gradually and with your buddy, following the safety plan you’ve agreed on.

• If symptoms persist or worsen, terminate the dive and seek medical evaluation as soon as possible. Oxygen toxicity isn’t something to wait out; professional assessment is essential.

• If you’re using any oxygen-enriched atmosphere on the surface (for example, a high-O2 treatment environment in a rescue scenario), communicate clearly with the surface team and medical staff about the exposure history.

How to prevent CNS oxygen toxicity on the next outing

Prevention is easier when you adopt a few steady habits. Here are practical steps you can weave into your routine:

• Gas planning: Know the oxygen content of your breathing mix and the maximum depth at which you should stay with that mix. Respect those depth limits, even if you feel good at shallower levels.

• Dive computer discipline: Use your device to track PO2 exposure. Many systems warn you if you’re pushing safe limits. Listen to the alarms; they’re not a nuisance, they’re a safety net.

• Buddy checks matter: Agree on a plan with your dive partner. Decide in advance how you’ll respond if either of you notices signs of oxygen toxicity.

• Keep exposure short: If you’re on a higher-O2 mix, lean toward shorter exposures at depth and longer surface intervals to break up any extended exposure.

• Be mindful of equipment and gas handling: Ensure regulators, tanks, and blend mixtures are correct for the planned dive. A small miscalculation can tilt the balance toward toxicity.

• Training and refreshers: Regular refreshers aren’t just a formality. They’re how you stay confident about gas limits and emergency responses.

Real-world context: why this matters for open water exploration

This isn’t just a theoretical quiz fact. In the field, oxygen toxicity has ended dives prematurely and forced quick decisions at depth. A diver who recognizes the early signs can switch gas, adjust depth, and head toward the surface with fewer risks. The more you practice reading the signs—plus the math and planning behind gas mixes—the more you’ll feel in control, even when the water around you is asking you to push your limits a bit.

A simple, human takeaway

Oxygen is a lifeline underwater, but like many powerful tools, it needs respect. The five classic signs—muscle twitching, nausea, dizziness, confusion, and convulsions—are not just a list to memorize. They’re a safety trigger, a signal that it’s time to reassess how you’re breathing, where you are, and what the plan looks like for the rest of the day.

If you’re curious about the science behind these signs, you’re in good company. Diving subjects mingle physiology with gear, and the best instructors blend practical know-how with a dash of curiosity. The result is a skill set you can trust when the water wants to push you in a certain direction.

A few final thoughts to keep you grounded

• Oxygen toxicity is about exposure, not just a single moment. Be mindful of how long you stay in high-oxygen conditions and at what depth.

• Your buddy isn’t just there for fun. They’re a critical part of your safety net. Agree on what to do if signs appear, and practice those steps in a controlled way during training.

• Modern equipment is a powerful ally. Dive computers, gas-checks, and clear stop sequences help you stay inside safe limits.

• It’s okay to adjust plans. If signs show up or if the computer flags a risk, you deserve the choice to back off and regroup.

Bottom line: stay curious, stay cautious, and lean on the tools you have. Oxygen is your friend in the right doses and at the right depths. It becomes a threat when exposure stretches beyond safe limits. Knowing the symptoms is not a quiz prep trick; it’s a practical, real-world shield that helps you enjoy the mystery and beauty of the underwater world with confidence.