CESA (controlled emergency swimming ascent)

When performing a CESA, a diver typically begins by signaling 'out of air' to their buddy, though the CESA is often practiced as a solo skill in training. The diver then looks up, clears the path, and begins a controlled ascent towards the surface, finning continuously. Crucially, the diver must exhale a continuous stream of small bubbles throughout the ascent, making a sustained 'ahhh' sound to ensure no air is held in the lungs.

As the diver ascends, the air in their lungs expands due to the decrease in ambient pressure. Continuous exhalation allows this expanding air to escape, preventing lung overexpansion injuries such as pulmonary barotrauma. The ascent should be slow and controlled, ideally not exceeding 18 metres (60 feet) per minute, which is typically slower than a rapid, uncontrolled ascent.

Upon reaching the surface, the diver should establish positive buoyancy by inflating their BCD (Buoyancy Control Device) or ditching weights, and signal to the boat or buddy for assistance. The CESA is designed for situations where a diver is out of air and their buddy is either not immediately available or too far to share air, and the surface is within a safe, shallow distance.

While a CESA is a fundamental safety skill, its practical application on a liveaboard trip is typically limited to very specific, rare scenarios. Liveaboard diving often takes place in remote locations and at greater depths than shallow training dives. Therefore, out-of-air emergencies at significant depth would generally necessitate an alternate air source ascent with a buddy or, if solo, a rapid, potentially uncontrolled ascent (emergency buoyant ascent) as a last resort, both of which carry higher risks.

However, the underlying principles of the CESA – maintaining an appropriate ascent rate and continuous exhalation – are vital for all ascents, emergency or otherwise. These principles mitigate the risk of lung overexpansion injuries, which can occur even during a normal ascent if a diver holds their breath. Regular practice of buoyancy control and awareness of ascent rates, reinforced by CESA training, makes every dive safer.

On a liveaboard, highly experienced dive guides and well-maintained equipment are standard. However, personal preparedness is paramount. Remaining proficient in CESA and other emergency procedures through occasional refresher courses or practice dives helps ensure you are a safe and confident diver, ready to enjoy the unique dive opportunities a liveaboard offers.

Myth: A CESA is for any out-of-air emergency, regardless of depth. Fact: The CESA is specifically taught for out-of-air situations where the surface is within a shallow, safe swimming distance (typically 6-9 metres or 20-30 feet). From greater depths, the risk of lung overexpansion injury from even slight errors in exhalation, and the increased risk of decompression sickness (DCS) due to rapid ascent, makes it unsuitable. Divers should primarily rely on their buddy's alternate air source at deeper depths.

Myth: You hold your breath on the way up to conserve air. Fact: This is a dangerous misconception. Holding your breath during any ascent, especially during an emergency, is extremely hazardous. As ambient pressure decreases, the air in your lungs expands. If this expanding air cannot escape, it can lead to severe lung overexpansion injuries (pulmonary barotrauma). Continuous, controlled exhalation is crucial.

Myth: A CESA is an uncontrolled dash to the surface. Fact: The 'C' in CESA stands for 'Controlled.' It is a deliberate, slow, and regulated ascent where the diver maintains an appropriate ascent rate (no faster than 18 metres or 60 feet per minute) while finning and continuously exhaling. An uncontrolled dash to the surface is an 'emergency buoyant ascent' or 'uncontrolled ascent' and carries significant risks.

Myth: You don't need to practice CESA once you're certified. Fact: Like any emergency skill, regular practice helps maintain proficiency. While you might not perform a full CESA often, reviewing the principles of continuous exhalation and controlled ascent during safety stops or at the end of a dive reinforces safe habits crucial for all ascents, thereby reducing the likelihood of needing an actual emergency ascent.