Chapter 11: Basic Underwater Skills

Breathing In and Under the Water


Study Question

As you read this page, look for the information that answers these questions:

What is the most efficient way to breathe from scuba?

What are the most common ways to clear water from a snorkel?

Breathing From Scuba

Breathing Under Water

Breathing from scuba is incredibly easy. You literally just stick the mouthpiece in and breathe in and out (through your mouth, not your nose).

As you already know, the number one rule of scuba diving is to breathe continuously and never hold your breath. What you need to be aware of is how to breathe.

  • The average adult’s vital capacity (maximum volume contained by the lungs and connected air passageways) is around five litres. Approximately one liter of this is what is known as “dead air” space — volumes of air in spaces such as the trachea (windpipe) that your body can’t use.


Shallow Breathing  
  • Let’s say you are breathing very shallow, inhaling just two litres of air instead of five. Half this air will remain in your body’s dead air spaces and be wasted.


  • Now let’s say your breathe as deeply as possible, inhaling the full five litres. Now your lungs are able to use fully 80 percent of your inhaled air.
  Deep Breathing


This is why it can be up to four times more efficient to breathe slowly and deeply while on scuba than it is to use short, rapid breaths.

In order to breathe continuously, any time you cannot inhale, you must be exhaling. Throughout your skills development sessions and open-water training dives, you will be doing a number of exercises that involve temporarily removing your regulator from your mouth. You want to develop the habit of exhaling a small, steady stream of bubbles any time this happens.

Breathing from a Free Flowing Second Stage

Modern regulators are designed to be fail-safe. In other words, if the regulator malfunctions, it will release a constant flow of air, rather than cutting off the air supply completely.

Free Flow

If you need to, you can breathe from the free-flowing regulator in order to have enough air to surface (although, if available, a buddy’s alternate-air-source is the better alternative). Your instructor may have you simulate a free flow in the pool by keeping the regulator purge button depressed.

To perform this skill, lean your head as far as you can to one side. If you don’t lean, the flow of bubbles might dislodge your mask, causing it to leak. Remove the regulator from your mouth, place the mouthpiece near your partially opened lips, and depress the purge button. You will be able to inhale off the steady stream of air just as you would when taking a normal breath

Snorkel Breathing and Clearing

Surface Swimming

Scuba divers uses snorkels primarily to conserve air while swimming face down at the surface. Breathing from a snorkel is much like breathing from a regulator. It is especially important to breathe deeply, as snorkels add to the “dead air” space already present in your body’s airways.

One thing that makes using a snorkel different is that water will enter the top of the snorkel barrel whenever a wave passes over your head at the surface or when it is submerged under water. There are two ways to clear water from a snorkel — the blast method and the displacement method.


  • Blast Method: The blast method involves forcibly blowing (exhaling) into the mouthpiece to force the trapped water out the top of the barrel. This procedure permits a swimmer at the surface to clear water from his snorkel without lifting his head.
  Blast Clearing
Blast Clearing
  • Displacement Method: With the displacement method, you can use expanding air to clear your snorkel as you ascend from a breath-hold dive. First, dive down to the bottom of the pool. On ascent, look up toward the surface, with the tip of the snorkel lower than the mouthpiece. As soon as your hand touches the surface, begin exhaling into the mouthpiece and continue to do so all the way to the surface. The exhaled air will force the water out of the snorkel tube. Immediately assume the natural position for snorkeling, with face in the water and snorkel tip pointed upward. Be aware that, although this method will work to some degree with any snorkel, it is best suited for use with snorkels that lack drainage valves at the bottom, such as those preferred by many experienced free divers.

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