Course Outline

Monitoring gas supply is one of the most important considerations for any diver on any dive. An out-of-gas situation can quickly become life-threatening. It is important for you to understand the options available that will get you back to the surface safely.

In the unlikely event that you are low or out of your breathing gas, STOP, BREATHE, THINK, and ACT.

You have two main options to consider.

  • The safest option is to get your buddy’s assistance. You will learn to locate, secure, and breathe from an air source supplied by a friendly donor—your buddy! This is a gas-sharing ascent.
    • Signal that you are out of gas to your buddy. Your buddy will then provide his or her primary mouthpiece and locate the alternate air supply. Don’t put the regulator in your mouth upside down! Link arms with your buddy, and once comfortably breathing, ascend together keeping eye contact, and monitor the console.
    • To simulate the skill, your instructor will ask you to swim horizontally for 10 meters/33 feet, and you will have a chance to act as both a receiver and a donor. This will be practiced in confined water before further training in open water.
  • What if you have no buddy and you are out of gas? This is an unlikely but very serious situation. It means you have not monitored your buddy or your gas supply. In the unlikely event that you have this problem, you will have to perform a controlled emergency swimming ascent (CESA).
    • You already have some air in your lungs. You ascend and slowly exhale all the way to the surface, keeping an open airway because the air will expand on ascent. Swim no faster than 9 meters/30 feet per minute on your way up. Make the aahhh sound through your regulator/mouthpiece, indicating that you have an open airway. This will prevent lung expansion injury.
    • This skill needs to be practiced! You need to perform a CESA if you are in 9 meters to 12 meters /30 feet to 40 feet of water or you are low or out of air and your buddy is too far away. Your instructor will simulate the skill in confined water while swimming horizontally. You will have time to practice this skill and understand that you can reach the surface on one exhaled breath.
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