We can reduce the No. 1 cause of visitor drownings in Hawaii, and as Civil Beat’s Nathan Eagle reported recently, it’s not about surfing or sharks, it’s about snorkeling (“Stand Up Or Die: Snorkeling In Hawaii Is A Leading Cause Of Tourist Deaths”).

As was reported, “Despite being touted as a leisure activity, snorkeling is the most common cause of injury-related death in the islands. In the last 10 years, more than half of all visitors who drowned in the Aloha State did so while snorkeling. Hanauma Bay, an iconic nature preserve, receives more than 1 million visitors annually. More tourists drown there than anywhere else in the state.”

Many are puzzled by this fact, and struggle to find a solution.

Breathing through a tube can quickly go awry, especially if you inhale water. Carbon dioxide is another problem.
Breathing through a tube can quickly go awry, especially if you inhale water. Carbon dioxide is another problem. Nathan Eagle/Civil Beat

The main advice provided by Nathan’s series is that we need to hire more lifeguards and that tourists should be in better shape before they come to Hawaii and get in the water. While this is true as far as it goes, it doesn’t solve the mystery of snorkel drownings and isn’t likely to lead to effective prevention.

As was noted, lifeguards have trouble detecting snorkel drownings: “How do you tell whether this motionless body is a live, breathing person who is trying to see something unusual, or a ‘floater,’ somebody who has suffered a catastrophic medical event and is lifeless and pulseless?”

In public health language, intervention by a lifeguard to save someone after a medical event has happened is called “secondary prevention.” More effective would be a strategy to prevent the medical event from happening in the first place. This is called “primary prevention.”

I believe that better understanding of the physiology of snorkel breathing can lead to a primary prevention strategy based on better education of novice snorkelers. The focus of this education needs to be on the risks of improper snorkel breathing, and on learning safe snorkel breathing. Teaching proper snorkel technique is easy to do and will save lives.

It Starts With The Breathing

The fact is, safe snorkel breathing is not the same as regular breathing. This is for two reasons. First, snorkel breathing uses a tube, which extends our airway “dead space” and reduces the portion of each breath available for gas exchange. Second, snorkel breathing takes place in water, which increases the risk of aspiration (inhaling water into the lungs). Each of these risks can contribute to medical distress and drowning.

The technique used for snorkel breathing matters. Long, slow, rhythmic breaths minimize the dead space and aspiration risk, while rapid shallow breaths increase them. Rapid shallow breaths can also increase aspiration risk by making it harder to interrupt the progress of water from the snorkel, to the mouth, to the airway and to the lungs. Rapid shallow breaths may also leave a smaller residual capacity in the lungs available for a snorkel-clearing exhale.

Most importantly, rapid shallow breathing reduces true lung ventilation (alveolar ventilation) because the increased airway dead space of the snorkel tube must be subtracted from the volume for each breath (tidal volume). It doesn’t seem like this would make a difference, but it can with rapid shallow breathing.

The amount of ventilation where it really matters, at the alveoli where oxygen is exchanged for carbon dioxide, is determined by this equation: alveolar ventilation = (tidal volume – dead space) * respiratory rate.

Using this equation to compare slow deep snorkel breaths with rapid shallow snorkel breaths, we see from the (attached) table that the difference in ventilation is significant, even when the total amount of air being “breathed” is the same (12 L/min). Compared to resting ventilation (4.2 L/min), slow deep snorkel breathing doubles alveolar ventilation (8.4 L/min) whereas rapid shallow snorkel breathing barely increases it at all (4.8 L/min).

This means that how we breathe will determine if a snorkel experience will be safe and enjoyable, or if it will involve fatigue, panic, cardiac ischemia, loss of consciousness or death. Once the impact of increased airway dead space is appreciated, the fact that snorkeling is the top activity linked with visitor drownings, even in shallow-water, makes more sense.

Learning Safe Snorkel Breathing (SSB) makes snorkeling a safer and more enjoyable experience for all involved. To accomplish this, we need help from snorkel rental and sales people, and snorkel tour staff, the visitor and tourism industry at large, and the general public. Teaching SSB should be part of the Hanauma Bay visitor education experience.

Measure Normal rest Snorkel slow Snorkel rapid
Tidal volume 0.5 L 1 L 0.5 L
Respiratory rate 12 breaths/min 12 breaths/min 24 breaths/min
Minute ventilation 6 L/min 12 L/min 12 L/min
Dead space 0.15 L 0.3 L 0.3 L
Dead space ventilation 1.8 L/min 3.6 L/min 7.2 L/min
Alveolar ventilation 4.2 L/min 8.4 L/min 4.8 L/min

Slow deep snorkel breathing doubles alveolar ventilation (8.4 L/min) compared to rapid shallow snorkel breathing (4.8 L/min). Note that snorkel breaths have increased “dead space.”

Safe Snorkel Breathing Tips

Breathe slow and deep: Place the mask on your face and the snorkel in your mouth and breathe in and out through the tube. Breathe slowly, deeply and cautiously with your mouth through your snorkel. It is important to take slow, deep breaths to flush air from the tube.

Relax and become aware of your breaths: The sound of your breathing through the snorkel barrel will be noticeable. No need to panic. You can always lift your head above water if you want, spit out the snorkel and breathe through your mouth like a normal swimmer. Get into the slow snorkel breathing rhythm, relax and enjoy the underwater scenery.

Breathe cautiously: Part of the slow, deep relaxed breaths is to better move fresh air into your lungs, and part of it is to prevent aspiration. You will get some water in the snorkel tube at some point, sometimes either due to waves, or by letting your head dip too low in the water. You will know this has happened when you begin to inhale and water enters your mouth. When this happens, first stop inhaling and hold your breath. Now you have two methods for flushing the water from the tube.

Flush: Learning to clear your snorkel is necessary.

• The easy method is to lift your head above water, spit out the snorkel and breathe through your mouth like a normal swimmer. Tip the snorkel tube back so it is upside-down, and the water just runs out of it. Often this can be done with one hand, assisted by tilting your head back. You are ready to resume snorkeling.

• The more advanced method is to keep the snorkel in your mouth and use your breath to flush the tube. Be sure you are floating at the water surface and not submerged, then exhale forcefully to expel all the water from the snorkel tube. This can be done quickly, with less disruption to your experience.

Safe Snorkel Swimming

Beyond breathing technique is the swimming technique. Jerky movements, body tension, flailing of the arms and legs require more air exchange, and make it difficult to calmly observe our surroundings.

Instead, move slowly through the water using easy flutter kicks. Float or glide when possible. Relaxed movement is in harmony with proper snorkel breathing, uses less energy, requires less oxygen and CO2 exchange, and fosters an enjoyable, perceptive, mindful and safe experience.

Safe snorkel progressive practice:

• Stand up on land, don mask and snorkel (no fins), and begin taking slow breaths deep snorkel breaths. Begin walking slowly (shuffling). Practice until you can comfortably do this for at least 5 minutes.

Practice flushing the snorkel with the same forceful exhale used to expel water from the snorkel tube. (In a group setting, this can done by the trainer tapping people, one by one, on the shoulder from behind as they are snorkel breathing and walking, and listening for proper technique.)

Next, go to a pool, or the beach if conditions are calm enough. Enter the shallow water, don mask and snorkel (no fins), and begin taking slow breaths deep snorkel breaths. Bend or squat until the mask is submerged and continue breathing. When you are comfortable, start floating in the shallow water. Practice until you can comfortably do this for at least five minutes.

Practice both methods of flushing water from the snorkel (manual and forceful exhale). If necessary, deliberately submerge 1-2 feet until water enters the snorkel, then flush.

If possible, take the opportunity to also practice the flutter kick with or without fins while in shallow water.

Once you are comfortable with these steps, you are ready to go out on the reef.

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