Home Snorkel Gear Review CO2 Build Up in Full Face Snorkel mask | How to prevent it!

CO2 Build Up in Full Face Snorkel mask | How to prevent it!

by Arjan Ligtermoet

It seems like new full face snorkel masks are released everyday, some expensive, some really cheap. Sometimes we hear frightening news that some masks actually put you in danger while snorkeling due to the CO2 build up inside the mask. How does this work and how can you check if your mask is safe to use?

Our top 3 Full Face Snorkel Mask

How Full Face Snorkelmasks are intended to be used

A snorkel mask is designed for recreational use. Just floating on the surface and comfortably looking down onto the fishies. What it’s not designed for is extensive open water swimming, freediving or swim practice. Just like with a normal snorkel and mask soon enough you will feel like you can’t catch your breath. This is due to the CO2 build up in the mask or snorkel while you exhaust yourself.
Dangerous Full Face Snorkel masks

Dead Space?! CO2 Build UP!

When we breath in and out we humans produce CO2. When we do an activity which exerts us, our body needs more oxygen to keep your muscles working and therefore our breathing becomes faster. At the same time we breath shallower which leads to our problem. Exhaled air contains more CO2 than the air we inhale. If we do this in a closed of space like a snorkel mask or a snorkel we won’t exhale deeply enough to push all the bad air out. Its like breathing in a closed of bag and the CO2 keeps on building until it becomes very toxic and we become unconscious.

Is it safe for kids?! Find out in our next article

The Good News

This all sounds pretty bad. Luckily the designers of snorkel masks have taken this into account. Therefore every mask has a breathing part and a looking part. The breathing part is locate near the mouth en looks a lot like a oxygen mask. This part seals the mouth and nose off from the rest of the mask. On the top of the ‘oxygen mask’ are little valves which are designed to only let in fresh air and don’t let any bad air escape to the looking part of the mask. The bad air is forced to the lower part of the ‘oxygen mask’ and flows to and out of the snorkel on the sides of the mask.
Dangerous Full Face Snorkel Masks

Separating the good masks from the bad

In some cheap and ill made masks the mechanisme as described above doesn’t work. It could be that the valves are faulty and don’t work or the ‘oxygen mask’ has a bad fit and bad air leaks down the sides of the mask. Checking if you bought a good snorkel mask is easy. First check if the breathing part fits neatly over your nose and as close to your face as possible. When you put on the mask and breath in it only the breathing part should fog up. The looking part should stay clear of any fog.

Important to remember

  • A snorkel mask is for relaxed snorkeling only and not made for freediving or extensive open water swimming.
  • Make sure the mask has the correct fit and that the breathing part fits neatly over your mouth and nose.
  • Always try on the mask and breath in it on land, only the breathing part should fog up
  • Always test a snorkel mask for the first time with a snorkeling buddy

So you don’t want to buy a Full Face Snorkel Mask anymore? Check out our top 3 full face snorkel mask alternatives

Safe full face snorkel masks:
Tribord EasyBreath on Amazon $ 59,99/€ 44,90
Ocean Reef Aria on Amazon $ 99,00/ € 89,50

Our review about the Ocean Reef Aria

Example of a FF Mask which isn’t safe: SeaBeast AF90


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Ashly March 5, 2018 - 2:43 am


Erik April 25, 2018 - 7:22 am

My wife and I went snorkelling two days ago (around midday, April 23, 2018.) She used a Tribord full-face mask that has a white frame and pink silicone interior, while I used a conventional mask and snorkel. Even though she is a better swimmer and more athletic than I am, she began to notice she couldn’t slow down her breathing after about 30 to 45 minutes of low-exertion snorkelling. She consciously tried to take slower breaths but felt a sensation of air hunger that rendered her ubable to fully catch her breath in the mask. Then she necame overcome with a sudden wave of extreme nausea and removed the mask. She successfully suppressed the urge to vomit and, once the mask was off, began to catch her breath in the fresh air. However, we were about 75 meters (82 yards) from shore and her episode of hyperventilation and nausea exhausted her too much to swim without me pulling her to safety.

She is a powerful, frequent swimmer and has never had a crisis in water throughout over 30 years of enjoying open water swimming and diving. This was the second time she had used a full-face mask snorkel. the first was a different model and for a shorter length of time.

As I am trained as a Registered Respiratory Therapist, I am fairly ceetain from her physiological symptoms and the accompanying circumstances that this potentially life-threatening incident resulted from gradually increasing partial pressures of CO2 in the mask. My wife exhibited classic signs of hypercapnea. The mask’s deadspace may have been high due to initially conservative, small breaths, and low tidal volumes secondary the low total lung capacity that corresponds to her 160 cm (5’3″) height.

I wonder how Tribord and other sellers have concluded that it is safe for consumers with a wide variety of total lung capacities and varying tidal volume characteristics to breathe from a limited range of mask sizes that have large amounts of deadspace.

My wife and I had a close call. I began struggling to get her to safety in time while our partners, who had already gone ashore, did not initially recognize that my waving to them (between periods of swimming and pulling her with me) were gestures for help. After we were out of the water, the sudden-onset nausea that had rendered her unable to swim to safety, which had followed the very gradually incremental hyperventilation, took the rest of the day to fully resolve.

Please notify Tribord, relevant product safety organizations and diving associations, and whoever might consider using Tribord full-face masks (or other similarly designed masks) that responsible research needs to be conducted to determine whether there is a sufficient level of product safety for these devices to promoted and sold.

After our experience this week, full-face mask snorkel equipment seems to be a very hazardous introduction to the recreational activity and sport of snorkelling.

I will also contact Tribord directly, but I’m thinking it’s worthwhile to comment on this publicly as well, so people can consider the potential risks before using this equipment.

Chris May 7, 2018 - 1:20 am

Just can’t believe this is a serious .When you INHALE, the air HAS to come from the snorkel tube, fresh air. Sounds like a situation where people are hyper-ventilating. Since the mask is not under any kind of pressure, CO2 can’t “build up” inside the mask. Your lungs are many times larger than the mask volume. I suggest you take slower deeper breaths, something you do in SCUBA. Or use a regular mask. Don’t understand the stupid full face thing anyway. It’s not for free-diving, clearly. It’d be like trying to go under with a ballon on your face keeping it afloat. And good quality low-volume mask has to better than this.

E May 7, 2018 - 2:26 pm

–>When you INHALE, the air HAS to come from the snorkel tube, fresh air.

>>Not true in some cases. It is possible to rebreathe exhaled air in certain cases, and not always possible to realize this is happening until the river becomes sypmtomatic of hypercap. After my wife’s close call, I discovered that one of the tiny rubber valve flaps between the inhalation and exhalation circuits had become dislodged, this permitting more exhaled air to enter the inhalation circuit with each breath. Like breathing out of a paper bag, each consecutive breath slightly elevated partial pressure of CO2 in the mask’s large amount of mechanical deadspace between the snorkel and the face.

You are right that these masks don’t even offer as good an experience as conventional masks and snorkels. A good driver can see that easily, but therein lies the dangerous problem: it has been documented that full-face masks appeal to the most novice of snorkelers. This is precisely the population most at risk because they do not know how to inspect the masks’ valve patency or why such an insignificant looking flap can have such monumental importance. They are more complicated than conventional snorkels and that ist’t obvious to first-time users.

Molla Wallace 305 Kuhio Shores May 9, 2018 - 2:39 am

I would suggest that if you are worried, pull the mask off your face for a few seconds every once in a while. The beauty of the mask is that it is easy to readjust it. If you are still worried take a flotation device out with you. The ease of the mask is just terrific. No more fogging!

E May 9, 2018 - 4:40 pm

Full face masks aren’tade safer just by being more expensive. The expensive Tribord mask that my wife used turned out to be just as dangerous as a cheap one. It’s best to avoid them all and go back to using conventional masks with separate snorkels.

E May 9, 2018 - 4:51 pm


The dangerous thing is that people get CO2 narcosis before they can get worried and then it’s too late even if they take off the mask. Before my wife had a chance to become worried, she was suddenly hyperventilating, violently nauseous, disoriented, and too exhausted to swim to safety. And she has been a strong open-water swimmer for decades with no prior emergencies. Since thousands of newbies are attracted to these masks, it’s almost certain that many will not fare as well as she did after I pulled her to shore. I agree, bringing a flotation device is essential, even if a little inconvenient.

Michael Lohse September 1, 2018 - 12:57 pm

I got Deep Vein Trombosis and Pulmonary Embolism, after swimming 3-4days 15-20 min ( relaxed breast stroke ) in the Pool. Auxiliary Vein & Subclavian clogged up. One night on Heparin intravenous in Hospital Emergency Room, CAT SCAN, Ultrasound Scan, etc. Xeralto 1100$+US for 60 Tablets.. and I think I was still be lucky.. I can not be sure it was the mask, but I am a healthy guy, jog regularly, average 30kms a week.. no health problems what so ever. Doctor said it is very unusual that you have blood cloths in your arm, most people have them in their legs. I hope this will be investigated by a federal agency, and more death will be prevented. I though it important to at least warn here..

Bill October 28, 2018 - 6:27 pm

Wow, just used one of these mass produced full face masks. Seemed ok at first, but after 10 minutes started to feel air hunger and uncomfortable. Cut the snorkeling short and returned. Perplexed as to the cause I did a search and found this article. Being an anesthetist I should have realized I was rebreathing co2 and diluting ambient 02%. It feels similar to the experience hiking at elevation in Nepal. Back to the simple face mask for me. Great idea, poor execution on some of these masks.

E October 29, 2018 - 1:25 pm

Yes, so dangerous. Even as a trained anaesthtist or resperatory therapist (my profession), who deals with mixes gasses and fights CO2 every day at work, it’s still not the first thing one thinks of when snorkeling and something feels wrong. Can you imagine how many others, with no training in the effects of CO2 narcosis at all, are at risk with these devices?

I have been in touch with the manufacturer of the expensive Tribord mask that almost killed my wife on a trip to Taiwan. The company’s representative basically said it is impossible for there to be CO2 build-up in their masks because of the theory behind the design. Never mind the facts in the water. Quite an irresponsible way to address this a life-threatening design flaw in one of their products.

If anyone finds these posts after a loved one has been killed by a Tribord full-face snorkel mask, post a reply on this thread and I can send you their correspondence to use a screen evidence that they were willfully marketing a dangerous product and their negligence caused the death.

Since my exchange with Tribord met a dead end, I don’t know what else to do that could resolve the dangers of such a popular product, except to warn people. It looks like 50ftbelow is urging caution with these products, and I appreciate that very much.

E October 29, 2018 - 1:45 pm

Bill, if you still have the mask, can you check the soft rubber or silicone flaps on the one-way inside the housing? If one is missing, dislodged, or propped open with a shell or sand, that’s where your rebreathed air leak was.

Tribord’s valves fall out easily, and it isn’t obvious to the swimmer that anything is missing. Without all of the valves functioning perfectly, the gas exchange theory behind full-face snorkel masks doesn’t work. When a valve flap is missing, the expired air shirt-circuits back into the inspiratory limb and is rebreathed so CO2 partial-pressure gradually elevates and the product becomes a death trap, just as bad as a faulty regulator.
After our close call, I discovered one of these little flaps was missing from my wife’s mask. I took photos and sent them to the manufacturer with an explanation of the issue. As mentioned above, they defended their design in spite of its deficiencies rather than taking the issue seriously.

Donna Rickard February 7, 2019 - 8:17 am

I have snorkelled for years and I love it as a relaxation and exploring the underwater sea life.
Today I decided to use (for the first time) a full face mask – Seablast AF 90. They never really appealed to me but I purchased it from a friend who was visiting from the USA and they purchased two online. No use for them once they returned to Nashville so I bought one off then to give it a go. It actually sat in my cupboard for approx 3 months as by unit I would reach for my fins and my old snorkel mask and venture across the road to admire and count the sea horses.
Today, after only 10 mins of relaxed snorkelling, mostly floating stationary and studying the sea horses I felt very unwell all of a sudden but I continued to move towards the rocks and admire the fish. Only lasted about another 5 mins and I had to get out of the water quick as I felt a little dizzy and nauseous. Within 3 – 4 I was at my front door but feeling worse.
No idea why I felt this way and after a few hours of resting (I felt so sickly) and peppermints I found myself googling to find out if it was related to the mask.
I can not believe what I have since discovered and this brand in particular is the cause of CO2 poisoning and known to cause unconsciousness.

This product should be banned

Joe January 27, 2020 - 6:54 pm

E, Erik, I’m glad you and your wife got through this. You said the mask had a faulty valve. So it is not the mask/design but the vale that may have been the issue. Why throw out the entire mask and design due to a human error in checking the operation of the equipment before use? I don’t disagree that maybe there should be some consideration for lung capacity which can be easily accommodated with a smaller intake compartment. This would prevent the ability of little to no C02 build up without first showing up with a fogging of the fresh intake compartment if the most exhaled breath is entering the fresh air chamber. I don’t disagree, equipment should be checked and faulty equipment not used. Flotation would have help in your case but was saved her is sticking with your swim/snorkel buddy.


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