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Gas Analysis: Protecting Yourself from Carbon Monoxide Poisoning

Gas analysis means more than simply ferreting out the fractions of oxygen and helium in your breathing mix, particularly in remote areas. Tec De-Ox CEO Eugenio Mongelli and DAN Europe founder and president Dr. Alessandro Marroni review the dangers of CO poisoning and what you can do to avoid it.



by Eugenio Mongelli and Dr. Alessandro Marroni
Header image: Temc De-Ox Carbon Monoxide analyses showing 30 ppm of CO. Not good! Photo courtesy of Temc.

We recently held a webinar that focused on analyzing your diving gas in order to detect potential carbon monoxide (CO) contamination of breathing gas. The webinar (see below), held on March 18, was supported by various diving agencies and organizations around the world.

It’s obvious that diving activities come with risks, and one liability is the quality of your breathing gas. In the current diving era, synthetic mixes, such as nitrox and trimix—to name just two—are widely available and frequently used. Unfortunately, the presence of  poisonous or life-threatening compounds in your diving gas is not as rare as you might think.

The mixing station at Zen Dive Co., Pasadena, California has a built-in carbon monoxide monitor. Photo by Francesco Cameli

Carbon monoxide (CO), an odorless, and tasteless gas that can build up in dive gas for a variety of reasons, as follows:

  1. Inefficient combustion of hydrocarbons (which, in turn, produces CO instead of CO2). 
  2. Oil pyrolysis in electrically powered air compressors, which is as a result of the compressor heating the breathing gas to more than 200°C/392°F during its last stage. This can occur if the compressor is not well maintained and or needs service.
  3. Exhaust from an endothermic engine, found in compressors using fuel or diesel engines.
  4. Cracking of oil residue in diving cylinders if the gas is not purged and the cylinder is not cleaned after a dive.
  5. Smoke from cigarettes.

Limits for CO in breathing gas must follow strict standards which have been issued by a variety of organizations and regulatory bodies including the European EN12021 CE standard, the US Navy Diving Manual (rev.7 2016 Point 4-3.1), and the U.S. Compressed Gas Association (CGA) (ANSI/CGA G-7.197). The consensus is that the limit of CO in breathable gas should be 5-10 ppm, or 0.0005%-0.001% concentration, which is an extremely low limit.

Gas Analysis Webinar. Who are those handsome italian men?

Some Medical Facts 

Carbon Monoxide Poisoning (COP) is a common medical problem worldwide. When at increased environmental pressure, CO’s ability to dissolve in blood and tissues is enhanced by its increased partial pressure.

COP can remain either completely undetectable or can present with a variety of symptoms: weakness, nausea, vertigo, headache, blurred vision, loss of consciousness, and coma. This list of symptoms is presented in order of frequency as well as the likelihood of exposure to a toxic CO concentration.

CO is 300 times more attracted to hemoglobin than it is to oxygen; so, when hemoglobin accepts oxygen atoms from CO, O2 is repelled, causing hemoglobin cells to suffer from lack of oxygen (cellular hypoxia). This process can affect every organ with long-term acute and chronic effects, including psychological disturbances. The cure is restoring hemoglobin’s affinity for oxygen with prompt and generous doses, displacing the unwanted CO molecules from blood, cells, and organs. 

Even if CO is expelled when exposure is over and normal air breathing resumes, the displacement process is slow, and hypoxic damage is still likely. Treatment with 100% O2 at 1 ATA will greatly accelerate the CO displacement process. Significantly quicker washout is obtained using Hyperbaric Oxygen administration (HBO), a treatment that exposes patients to high concentrations of oxygen at higher than 1 ATA. The following half-life figures make it clear just how effective HBO treatment is in expelling CO: 

  • CO half-life: 300 minutes
  • CO half-life in air at 1 ATM: 90 minutes 
  • CO half-life in 100% O2 at 1 ATA: 35 minutes
  • CO half-life in 100% O2 at 2.5 ATA: 22 minutes. 

We generally learn (or we should have been taught) about COP during our first open water course, and divers should take note of it.

Over the last 15 years, CO analyzers designed for diving applications have not been available. The existing analyzers on the market were costly, not portable, required extensive calibration and setting adjustments, and did not have the proper sensitivity. The only way to measure CO was to use chemical tubes, which required extensive operator expertise and expensive devices. Without the appropriate technology, CO accidents happened.

Temc De-Ox makes one of the only portable CO monitors on the market. Photo by Temc De-Ox.

As a result, my company TEMC DE-OX began developing its own CO analyzer with the specific goals of simplicity (of use and maintenance), mobility, battery power, and affordable price. In 2008, we released the DE-OX SAFE analyzer, which not only met, but exceeded, our product goals.

I dive around the world, and I always bring my own unit with me. I check the air quality at diving centers, and always ask the owner’s permission to perform the test.  What I’ve found is that it’s not uncommon to find the presence of CO, but even if the concentration is within a safe limit, it’s enough to alert staff that something may have gone wrong during the filling process.

Dive shop owners are generally incredulous, and they tend to blame the analyzer at first but, once they understand that something could have gone wrong, they want to know what to do to prevent that from happening. I alert them to the risks of running an unserviced compressor and to the possibilities of filter, oil, or air intake malfunctions, along with the causes listed above. After all, ignoring your gas quality could come with a price you don’t want to pay.

Inline analysis. Photo courtesy of Dive Manchester UK: divemanchester.co.uk

The worst possible scenario is when dive shop owners understand, but because their shop hasn’t caused any (reported) accidents, they aren’t convinced there is a need. Unfortunately, ignoring your gas quality comes at a price no one wants to pay.

I was contacted some years ago by our Russian distributor who affirmed the value of  his CO integrated trimix analyzer. He reported that he had filled some rebreather cylinders using a gas booster to be used for a dive at 150 m/492 ft. But, during analysis, he had found the trimix contained 150ppm CO because the helium cylinder that was used had contained a soldering mix likely with argon, and the old mix hadn’t been thoroughly drained before being refilled with helium. The distributor now highly encourages divers to conduct a gas analysis before every dive.

Also, some Maldives friends of mine reported that they had detected over 50ppm of CO in their tanks, likely due to the exhaust from their liveaboard compressor’s fuel engine. The wind had changed direction during filling, directing the CO into the tanks. Luckily, the analyzer alerted the divers when it detected the high concentration.

Now, on every dive, wherever you are, please take care of yourself and analyze your gas. The life you save could be your own. 

Eugenio Mongelli was born in Rome, Italy, in 1965, and has been deeply attracted to the sea, diving, and scuba gear technology since childhood. Having learned to scuba dive in 1982, he first dived a closed oxygen rebreather in 1984 and then began using electronic closed-circuit rebreathers from the mid-1990s. Mongelli became a diving instructor in 1991 and is currently a free diving and scuba diving master instructor, and a rebreather and trimix instructor with FIPSAS, CMAS and TDI. 
Mongelli was happily surprised to discover aquaCORPS magazine in the early ‘90s, which opened his mind to new horizons in diving that have become his life path. A doctor in management engineering and a former naval officer, he founded the TEMC DE-OX company in 1996 with the intent of providing digital gas analyzers specifically designed for both sport divers as well as the military and commercial diving communities. Since then, he closely follows the development of technical diving in all aspects of training, learning, designing new gear, and has been an active part of the global diving community.  

Prof. Alessandro Marroni, MD, MSc, FUHM, FECB (aka “Doc”) is the founder and President of DAN Europe. He is a diving and hyperbaric physician and researcher, specializing in Occupational Medicine, Anesthesiology, and Intensive Care. A passionate diver since his early years, he learnt scuba at the age of 13 and has been an active Instructor since 1966. Author of over 250 scientific papers and publications, he is particularly active in underwater medicine research, with special interest in the prevention of barotrauma and dysbaric illnesses in diving, and in the development of advanced techniques for remote diver’s physiological monitoring and of bidirectional diving telemedicine. He serves as Vice President of the European Committee for Hyperbaric Medicine (ECHM), President of the European Foundation for the Education in Baromedicine, Secretary General of the European College of Baromedicine, and the past President of the International Academy of Underwater Sciences and Techniques, the International Congress on Hyperbaric Medicine, and the European Underwater and Baromedical Society.



Creative director and photographer Brenda Stumpf conjures up a crush of living, breathing mermaids and monsters that dwell deep within our collective unconscious.




“Working at depth is a particular challenge with models and I was fortunate to have a fantastic crew and a subject who was not afraid to dive deep.” 

“Shooting in closed environments allows for more exploration in costuming and effects that might become too dangerous in the open water.  In this shot, with the help of a fantastic hair and makeup crew, we were able to create an underwater ‘ivy jungle’ that our model could interact with to create an image that is filled with movement.”

“California diving is extraordinary, but it is also difficult – cold, and often hampered with poor visibility.  On this day, we struck gold… late summer, water about as warm as it would get in the upper 60’s and visibility around 50 feet.   Under these conditions, Mermaid Virginia was a rockstar… and managed to perform effortlessly for more than double the usual time you would expect from a model under cold water conditions.”


“While not underwater, this is one of my favorite images.  The visibility that day was pure green soup out at the island – maybe 2 or 3 feet… so we improvised and pivoted our plan to do some shoreline images.  Paul became the pirate who finds Mermaid Virginia – washed ashore. The look on his face and the commitment to the story that they both provided – makes this image complete magic to me.”

“The sequences we shot in Mexico are some of my favorites… and this image rises to the top.  I wanted to portray the duality of the beautiful mermaid who is really a monster in disguise.  Above the water, she is beautiful and intriguing, and under the surface, she is all murder and terror.  Mermaid Jessica was able to pull this one due to her extraordinary presence and incredible costuming skills.  As a bonus, we had a few little fish that kept popping into the shots – that I think really added to the overall effect.”

“Nestled deep in the mangroves of the cenotes of the Yucatan, we found a spot that became the perfect ‘lair’ for our siren/monster mermaid.”  

“Another beautiful day on Catalina Island.  If you depart from the dive park, and explore around the island a little… you can find amazing locations at shallow depth, but with a ton of structure and beauty.”  


“This was such a fantastic moment.  Mermaid Linnea is a natural talent underwater, and so calm that all the garibaldi came in to check her out.”  

“Nestled into an underwater cave, this sweet mermaid glances out into the world above.  Mermaid Elisa brought this creature to life and is an extraordinary underwater talent.  She was able to work the rather difficult costuming with ease.”

“A little behind the scenes captured while we were on location for two weeks shooting in multiple locations throughout the Yucatan peninsula.  Best crew, and best models, best team.”  


Photo Details:

Header Image Credits: Location: Simi Valley, CA Model: Traci Hines Safety Diver: Virginia Hankins. “Mermaid Traci was an absolute delight to work with.  This was her first underwater mermaid photoshoot and I’m thrilled at how well it came out. “

Alissa Photo Credits; Location: Roatan, Honduras; Model: Alissa Quon; Safety Diver: Virginia Hankins

Virginia Photo Credits: Image 1; Location: Simi Valley, CA; Model: Virginia Hankins; Hair/makeup: Chrystina Yu Makeup & Natasha Johnson; Image 2; Location: Catalina Island, CA; Model: Virginia Hankins; Safety Diver: Jon Council; Image 3; Location: Catalina Island, CA; Models: Virginia Hankins, Paul Suda; Safety: Mike Varga

Jessica Photo Credits: Image 1; Location: Playa Del Carmen, Mexico; Model: Jessica Dru Johnson; Safety Diver: Mike Varga; Image 2; Location: Playa Del Carmen, Mexico; Model: Jessica Dru Johnson; Safety: Mike Varga

Linnea Photo Credits: Image 1; Location: Catalina Island, CA; Model: Linnea Snyderman; Safety: Jon Council; Image 2; Location: Catalina Island, CA; Model: Linnea Snyderman; Safety: Jon Council

Elisa Photo Credits: Location: Playa Del Carmen, Mexico; Model: Elisa Buller; Safety: Mike Varga

Virginia & Jessica Photo Credits: Location: Playa Del Carmen, Mexico; Models: Virginia Hankins, Jessica Dru Johnson; Safety: Mike Varga

Brenda Stumpf has been diving and making photos for the past 12 years in both closed and open water environments.  She specializes in fine art and portraiture and can be found passport in hand, ready to head out to another great adventure. You can find more on her website: Brenda Stumpf. For more mermaids, check out her book: The Mermaid Project.

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