Carbon Monoxide is a silent danger in breathing gas for divers—and here’s how to stay safe

Which gas should be avoided in our air supply due to its hazardous effects?

• A. Carbon Dioxide
• B. Oxygen
• C. Carbon Monoxide
• D. Nitrogen

Answer: (C)

Carbon monoxide should be avoided in our air supply due to its hazardous effects on the body. It is a colorless, odorless gas that can enter the bloodstream through the lungs and bind to hemoglobin, which significantly reduces the blood's ability to carry oxygen. This can lead to symptoms ranging from headaches and dizziness to more severe consequences, such as unconsciousness and even death in high concentrations. In the context of diving, the presence of carbon monoxide in breathing gas can be particularly dangerous because it may not be immediately detectable to the diver. It can lead to serious health issues, including carbon monoxide poisoning, which can occur without warning under certain conditions. Other gases mentioned may have their own risks and considerations in diving scenarios, but carbon monoxide stands out due to its acute toxicity and the specific dangers it poses in an underwater environment where proper oxygenation is critical for survival.

Outline (brief skeleton)

• Hook: Carbon monoxide as the quiet danger in air supplies

• What CO is and how it harms the body

• Why CO matters for open-water training and underwater work

• How CO can show up in breathing gas (sources and scenarios)

• Signs to watch for and why detection isn’t always obvious

• Prevention: maintenance, testing, and safe air sources

• Quick takeaways and a closing thought about responsibility and awareness

The silent threat in your air supply: carbon monoxide

You’ve probably heard about carbon monoxide (CO) as a danger in homes and garages, especially around heaters or engines. But CO isn’t just a terrestrial problem. In open-water training and underwater work, CO can slip into the air you breathe, and it’s the kind of hazard that doesn’t announce itself with a smell or a loud alarm. It’s colorless and odorless, a ghost gas that travels with you when you’re counting on air that’s supposed to keep you alive. So, let’s break down what CO is, why it’s so dangerous, and how divers can keep it out of their lungs.

CO: what it is and why it matters

Carbon monoxide may be small in size, but it’s big on danger. The basic story is simple: CO is a gas that binds to hemoglobin in your blood much more strongly than oxygen does. Hemoglobin is the protein that carries oxygen from your lungs to the rest of your body. When CO crowds in, it hogs the oxygen-transport role, leaving your tissues starved for oxygen. The result isn’t immediate pain—it can start with something as mild as a headache or dizziness, but it can escalate quickly to confusion, fainting, or worse, especially in the high-stakes environment of underwater gas exchange.

Here’s the thing to remember: the body’s oxygen supply is already stressed when you’re underwater. Your tissues rely on every breath; you’re not just fighting gravity, you’re fighting time. CO ups the stakes because the symptoms can mimic ordinary fatigue or dehydration. That means you might attribute a strange feeling to a rough dive, a long day, or a poor night’s sleep—when, in fact, CO is the culprit.

Why CO stands out in the underwater world

Underwater, the oxygen you’re delivering becomes even more critical. If CO taints your breathing gas, you’re not just dealing with a head cold or a headache; you’re dealing with a gas that sabotages the very mechanism that keeps you conscious and mobile under pressure. Early symptoms like headaches or lightheadedness can creep in, and you might push through them, thinking you’re just having a rough day. But the poison is stealthy. In some cases, exposure can progress without the diver realizing something is wrong until it’s too late.

Compare CO with other gases you’ve heard about in the same breath—oxygen, nitrogen, carbon dioxide. Each has risks, sure. Oxygen can become toxic if you push it too high for too long; nitrogen can cause narcosis at depth; carbon dioxide can build up and drive us to breathe harder. But carbon monoxide is different: it doesn’t need a lot of the gas to cause problems, and its signs can be slow to show. That combination makes CO a standout hazard in air supplies used for training and exploration alike.

How CO can sneak into breathing gas (and how to spot the red flags)

Gas systems for diving aren’t just about the numbers on a dial; they’re about ensuring every breath you take is clean. CO contamination can come from several sources:

• Faulty or poorly maintained compressors and intake systems near exhaust or vehicle traffic

• Contaminated fill stations where air sources mix in a way that introduces CO

• Proximity to engines or other combustion sources during air filling or storage

• Improperly maintained air storage or transport lines where leaks allow exhaust to seap in

Because CO is invisible and odorless, you won’t smell it or see it coming like you might with a stuffy fill line or leaking valve. That’s why the emphasis in training and in real-world operations is on prevention, not mitigation after the fact.

As a diver, you might instrument with your own vigilance:

• Regular equipment checks that include testing the air source with appropriate detectors

• Confirming that a reputable fill station uses properly calibrated analyzers and follows safety protocols

• Being aware of anything unusual about your breathing gas—if you notice abrupt headaches, dizziness, or a sense of heaviness while breathing, stop and assess

If CO does slip in, symptoms can be subtle at first. A sudden headache after a light morning session, dizziness after a short swim, or unusual fatigue that doesn’t fit the day’s exertion—these can be clues. But remember, CO’s danger isn’t just about feeling unwell. It can quietly reduce your ability to deliver oxygen where it’s needed most, especially under stress or when power and precision are essential.

Prevention: keeping CO out of the loop

The best strategy is practical prevention. Treat your air supply with respect, and treat every fill as a potential risk if you skip the checks. Here are some common-sense steps that help keep CO at bay:

• Use a reputable air source and fill station with routine maintenance and calibration schedules. If a station can show you logs and test results, that’s a good sign.

• Request or rely on gas analysis that includes CO risk assessment when possible. Oxygen content should be accurate, but if you can confirm CO safety, that’s even better.

• Have access to a CO detector designed for compressed air systems, especially in environments where exhaust sources or engine noise nearby could influence air intake.

• Pay attention to the surroundings. If a filling area is near engines, vehicles, or other potential CO sources, raise a flag and choose a safer location or a different gas source.

• Maintain your equipment. Keep hoses, connections, and valves clean and free of leaks. A small crack can become a bigger problem if it disrupts how air flows through the system.

• Stay trained and informed. Understanding the signs of gas contamination and the proper response protocols is part of being a responsible open-water diver.

This isn’t just about a single checklist; it’s about building a culture of safety where gas quality isn’t an afterthought. In a sport that rewards precision, a little extra attention to air quality pays off in confidence and peace of mind.

What to do if you suspect CO exposure

If you notice symptoms that don’t quite fit the day’s activity—and they pop up after you breathe from a particular tank or regulator—stop using that gas. Switch to a known-good source and seek medical advice if symptoms persist or worsen. If you’re in a training environment, alert your instructor or supervisor so the team can check the gas supply and assess the situation.

Remember, in underwater work you don’t want to gamble with oxygen delivery. It’s not about fear; it’s about prudent caution. CO exposure can escalate quickly, and in the worst-case scenario, it can be life-threatening. The moment you sense something off, it’s okay to opt for a safer air source and regroup rather than press on.

A few practical takeaways you can carry

• Carbon monoxide is the gas to watch out for in air supplies. Its stealthy nature makes it especially dangerous underwater.

• CO binds to hemoglobin far more strongly than oxygen, which means your body’s oxygen transport is compromised long before you notice something is off.

• The underwater environment magnifies the risk. Reliable air quality checks and responsible station practices aren’t optional; they’re essential.

• Prevention is your best defense: use trusted fill stations, test air when possible, and use detectors in high-risk environments.

• If symptoms appear, pause, reassess, and switch to a clean air source. Your safety depends on acting decisively.

A closing thought: stay curious and careful

There’s something almost comforting about following a steady process when you’re underwater—knowing that the water around you isn’t the only thing you’ve got to manage. Gas quality is part of that process. CO is a reminder that danger isn’t always loud; sometimes it’s a quiet, almost invisible thing that demands vigilance, a good routine, and a bit of practical skepticism.

If you’re curious about how this all ties into the broader learning you’ll encounter in your open-water journey, you’ll see a lot of crossover between theory and application. The same principles apply—beware unseen hazards, verify what you’re given, and communicate openly with your team. It’s not just about knowing the right answers; it’s about building habits that keep you and your teammates safe when the pressure is on and the water is around you.

In the end, CO’s danger isn’t about one moment of alarm. It’s about respect—respect for the air you breathe, respect for the equipment you rely on, and respect for the teamwork that makes underwater exploration possible. With that mindset, you’re not just prepared for the checks or the questions that come your way—you’re ready to breathe easy, no matter how deep you go.