緊急浮上

Emergency ascents are broadly categorised by the diver's ability to control their ascent and whether they have access to an air source. The primary goal in all scenarios is to avoid holding one's breath, which can lead to severe lung overexpansion injuries due to Boyle's Law.

Controlled Emergency Swimming Ascent (CESA): This is performed when a diver runs out of air at a shallow to moderate depth (usually less than 18 metres or 60 feet) but can still control their buoyancy and ascent rate while continuously exhaling. The diver slowly kicks upwards, maintaining an ascent rate slower than or equal to 18 m/min, continually exhaling a small, steady stream of bubbles. The aim is to reach the surface safely without immediate assistance.

Buddy Breathing Ascent: If a diver runs out of air but has a buddy nearby, they can share air from their buddy's alternate air source. Both divers ascend together, sharing the air source and maintaining a controlled ascent rate, often performing a safety stop if time and air permit. This requires excellent communication and practice.

Uncontrolled Buoyant Ascent: This is a worst-case scenario where a diver's buoyancy becomes positive and they cannot control their ascent rate, often due to a lost weight belt or severe equipment failure. In such cases, the diver must focus entirely on continuously exhaling as rapidly as possible to prevent lung injury. While less ideal, it is still preferable to holding one's breath during a rapid ascent.

Regardless of the specific type of emergency ascent, several core principles must be followed to maximise safety. Continuous exhalation is non-negotiable; as ambient pressure decreases during ascent, air within the lungs expands, and failure to exhale allows this expanding air to overstretch and damage lung tissues. The exhalation should be a steady, small stream of bubbles, not a forced expulsion.

Maintaining a slow and controlled ascent rate is also crucial. While the maximum recommended rate is 18 metres (60 feet) per minute, slower is generally better if possible. This allows the body more time to off-gas absorbed nitrogen, reducing the risk of decompression sickness. Divers should use fin kicks to control their upward movement, avoiding a rapid, uncontrolled rise.

Other important steps include jettisoning weights only as a last resort in uncontrolled buoyant ascents, and always looking up and around during the ascent to avoid collision with boats or other obstacles. Upon reaching the surface, the diver should inflate their BCD to establish positive buoyancy and signal for help.

Liveaboard diving typically involves multiple dives per day, often in remote locations, making emergency preparedness even more vital. Dive briefings on liveaboards will always cover emergency procedures specific to the vessel and dive sites, including how to signal for help and where emergency equipment is located. Divers should pay close attention to these briefings and ask questions if anything is unclear.

While liveaboard dive guides are highly experienced and trained to handle emergencies, the primary responsibility for safety always lies with the individual diver. Regular checks of your equipment, including your alternate air source and gauges, are essential. Ensure your BCD and regulator are well-maintained before and during the trip.

Practising CESA in a controlled environment, such as during an Open Water or Advanced Open Water course, builds muscle memory and confidence. This preparation is invaluable should an emergency arise during a liveaboard dive, where quick and correct action can be the difference between a minor incident and a serious one. Always dive within your training limits and communicate any discomfort or issues to your buddy or guide immediately.

Myth: You should shoot straight to the surface as fast as possible in an emergency. Fact: While an emergency implies urgency, an uncontrolled, rapid ascent significantly increases the risk of decompression sickness and lung overexpansion injuries. The priority is to ascend as slowly as safely possible, continuously exhaling, to mitigate these risks. A controlled emergency ascent is always preferred.

Myth: Holding your breath briefly during a rapid ascent is fine if you're panicking. Fact: Never hold your breath during any ascent. Even a slight hold can cause the air in your lungs to expand rapidly as external pressure drops, leading to potentially fatal lung overexpansion injuries. Continuous, even gentle, exhalation is critical at all times.

Myth: Liveaboard dive guides will handle any emergency ascent for you. Fact: While liveaboard dive guides are highly trained and will assist, each diver is ultimately responsible for their own safety and preparedness. You must know and be able to execute emergency procedures yourself, as the guide may not be immediately beside you or may be attending to another diver.