Most people don’t think much about carbon monoxide (CO). It just isn’t that big of a problem, fortunately. However, it is a problem, and one we can easily address for an initial investment of about $300 and then another $140 every couple of years. Compared to the cost of most dive gear this is a small price to pay for the piece of mind in knowing the gas you are breathing is not contaminated with the tasteless, odorless gas known as carbon monoxide.

Honestly, we never gave it any thought before. None of our scuba instructors had ever mentioned carbon monoxide contamination during any of our scuba courses. And, as far as we knew, no one was getting injured or dying from CO poisoning during dives. We were very wrong. Just in the past few years there have been three CO related deaths and two injuries that we know of. That’s without doing any research. There are likely more. There are also likely to be many injuries and possibly deaths that just weren’t investigated enough to discover CO was the culprit.

How does CO get in our scuba cylinders?

There are a few ways carbon monoxide can get into our scuba cylinders. The most common causes are running a vehicle near the compressor air intake (vehicle exhaust is comprised mainly of CO) and running a compressor so long it starts to produce CO. While many compressors have filters in place to filter our contaminants in the air, they don’t always work, and sometimes may even contribute to the contamination.*

Regardless of how carbon monoxide gets into the scuba cylinder, once it’s there it’s dangerous to the diver. The commonly accepted level of CO in regular grade E scuba air is 10 parts per million (ppm). Anything above this can be dangerous, even deadly, to the diver breathing the contaminated air. While that amount of CO is harmless at the surface, as with every other gas, as you descend the concentration of the gas multiplies with the pressure increase (Dalton’s Law). That 10 ppm becomes toxic to the diver with the increase in proportion.

The commonly accepted level of CO in oxygen safe scuba air is 3 ppm. The reason for the lower limit is that CO, being a contaminant, will increase the risk of fire or explosion if combined with rich percentages of oxygen. While greater than 3 ppm is “safe” to breathe at depth, it is not safe to mix with oxygen.

The way we look at it is if there’s any carbon monoxide in the gas we are about to breathe underwater there’s a problem. There should be no CO moving through the compressor filters and to find any indicates there is a problem somewhere that will only get worse.

What does CO do to our bodies?

During the respiratory process we normally breathe in air containing approximately 21% oxygen and 79% nitrogen (there are traces of other inert gasses). Only about 5% of the oxygen gets used by our bodies and binds to our hemoglobin. Hemoglobin is the part of our blood that carries oxygen throughout our bodies to oxygenate our organs and tissues. The problem with carbon monoxide is that hemoglobin likes it a lot more than it likes oxygen. In fact, hemoglobin has an affinity for CO that is 225 times greater than for oxygen. So when there is both oxygen and CO in a scuba cylinder, the CO will always win. This means oxygen will not bind with our hemoglobin and our organs and tissues will not get oxygenated. Essentially, our bodies become starved of oxygen leading to a black out. Under water this leads to drowning

When people come to the emergency room for exposure to carbon monoxide we have them breathe 100% oxygen for at least 12 hours to wash it out of their systems. The treatment for a diver who has been exposed to CO and survived long enough to get back to the surface is to put the diver in a hyperbaric chamber to expose him/her to 100% oxygen while at pressure.

So how do you detect CO?

Carbon Monoxide Analyzers

There are currently two carbon monoxide analyzers being manufactured specifically for scuba diving purposes.

Analox EII CO Carbon Monoxide Analyzer

C-Squared CO Analyzer (being sold as an Oxycheq analyzer)

Both analyzers do the same job and are in the same price range. They are both compact and easy to travel with. Both require sensor replacement about every two years. So it really doesn’t matter which one you choose.

“But I only dive in the US so I don’t need one”

The two cases we know of that we stated were injuries occurred in the US at a popular dive shop. The shop hadn’t had any issues with their gas before those incidents or since then. It happens! For about $300 you can make sure it doesn’t happen to you!

We are so passionate about this issue because we had a friend fall victim to CO poisoning. He didn’t get injured. He died. His maximum depth on his last dive was 40 feet. His actions showed he knew something was wrong just seconds before he passed out, but there wasn’t enough time for him to react before blacking out. And even if he had, once CO gets in your body the only treatment is exposure to high percentage of oxygen, something that wasn’t going to happen on the dive. A CO analyzer would have prevented his death. A CO analyzer can prevent yours.

* See the following article for more information on how compressors can create carbon monoxide –
Gas Analysis – Keeping yourself safe while cave diving!

At Chipola Divers we test our gas quarterly as well as analyzing every cylinder we fill for carbon monoxide.