Monitoring gas supply is one of the most important considerations for any diver on any dive regardless of experience and certification level. This is a habit that even technical instructor-trainers, cave divers, and rebreather divers are careful to cultivate.
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. Now is the time to start to plan your bottom time based on your actual documented gas consumption rate. Your instructor will help you.
In the unlikely event that you are low or out of 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 regulator and locate his or her alternate air source (AAS). 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 your gauges and PDC.
- 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 or you have suffered from a catastrophic equipment failure. In the unlikely event that you have this problem, you will have to perform a controlled emergency swimming ascent (CESA).
- Since you already have some air in your lungs, you can use this breath to help you reach the surface. 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. Exhale continuously while making an aahhh sound through your regulator mouthpiece, indicating that you have an open airway. This will prevent lung expansion injury. Do not remove your regulator—this will help you avoid inhaling water.
- This skill needs to be practiced. A CESA can be initiated if you are in 9 meters to 12 meters/30 feet to 40 feet of water and if you are low or out of air and your buddy is too far away to assist. 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.