Understanding PADI's Emergency Ascent Procedures

During the PADI Open Water Course, one question causes student divers to tear their hair out in confusion. Students are asked during the knowledge-review questions and again during the open water certification quizzes and final exam to “arrange the four out-of-air and low-on-air procedures in order of priority from one through four.” Even if they manage to locate the correct answer in open water manual, many students do not understand the reason for the order.

Four Emergency Ascent Procedures

PADI recognizes four emergency ascent procedures for low-on-air/out-or-air situations:

Normal Ascent – The diver ascends at a normal rate with normally functioning equipment (e.g., if the diver is low on air).
Alternate Air Source Ascent – The diver ascends at a normal ascent rate, breathing from the alternate air source regulator of his buddy (e.g., the diver is out of air).​​
Emergency Swimming Ascent – The diver ascends on his own by swimming to the nearby surface without a working regulator (e.g., the diver experiences an equipment failure).
Buoyancy Emergency Ascent – The diver ascends alone by dropping his weights and floating to the surface. He usually exceeds a safe ascent rate.
[Eliminated] Buddy Breathing Ascent – PADI has eliminated the optional buddy breathing from the updated open water course standards. In the past, buddy breathing was taught as an optional skill. In buddy breathing, the diver ascends with his buddy sharing only one working regulator between two people by passing it back and forth between them.

Normal Ascent

If it's safe to do so, the preferred method of ascent is a normal, planned ascent. This point is where the confusion starts for most students, who wonder how can a diver make a normal ascent when he is out of air. Remember, the question deals with out-of-air and low-on-air situations. If a diver is merely "low-on-air" but not completely out of air, he needn't panic, drop his weights and rocket to the surface. In most situations, a diver who is merely low on air can alert his buddy, make the hand signal for “end the dive/ ascend” and make a normal ascent to the surface. This option is included in the question to remind students that running low-on-air is not immediately a cause for panic, and should be dealt with in a calm and controlled manner by ending the dive and making an immediate, but controlled, ascent.

Alternate Air Source Ascent

The alternate air source ascent is the second-best option for emergency ascent procedures because it allows divers to maintain a normal ascent rate and buddy contact. The out-of-air diver signals “out-of-air” to his buddy, secures his buddy's alternate air source and breathes normally from the alternate air source while the two divers make an immediate, controlled ascent to the surface.

This option offers several advantages in comparison with the remaining options:

• Each diver keeps a regulator in his mouth during the ascent and can breathe normally through the entire trip to the surface.
• The divers have sufficient air to maintain a safe ascent rate, which reduces the risk of decompression illness.
• They stay together as a buddy team, so the diver donating air can calm the out-of-air diver and help him to ascend slowly and safely.

Emergency Swimming Ascent

The Emergency Swimming Ascent is ranked third because when performed correctly, it allows an out-of-air diver to ascend without putting his buddy at risk. In an Emergency Swimming Ascent, a diver releases air from his buoyancy compensator (BCD) to avoid exceeding a safe ascent rate, and breathes out slowly to avoid a lung over-expansion injury. Although no air remains in the diver's tank, he leaves his regulator in his mouth to avoid accidentally inhaling water, so there is no risk of drowning. In addition, he may be able to get few additional breaths from the tank as he ascends to a shallower depth.

This is the point at which many open water certification students get confused. The Emergency Swimming Ascent is performed when a diver is completely out-or-air and does not have an alternate air source available, either because he cannot contact his buddy, or because his buddy's alternate air source regulator has failed.

Buoyant Emergency Ascent

A Buoyant Emergency Ascent is basically the worst thing that you can do, short of drowning. A diver who is out-of-air, unable to contact his buddy, and too deep to perform an Emergency Swimming Ascent can make a Buoyant Emergency Ascent by dropping his weights and rocketing to the surface. The air in his buoyancy compensator will expand according to Boyle's Law as the diver ascends, and he will fly upwards at a continuously accelerating rate until he reaches the surface. The diver should attempt to open his airways by exhaling as he ascends and may extend his arms and legs to try to slow his ascent, but chances are that he will reach the surface in bad shape. The diver exceeds the maximum safe ascent rate and risks decompression illness and pulmonary barotrauma. Because he is ascending in an uncontrolled fashion, he also risks injury from boat traffic. 

Eliminated: Buddy Breathing Ascent

The Buddy Breathing Ascent was ranked fourth in the past, but has been eliminated from PADI's current list of emergency ascent procedures because of the risk and difficulty involved in the skill. Buddy Breathing Ascents require two divers to share a single regulator between them.

A diver breathes two breaths and then passes the regulator off to his buddy, who breathes two breaths and hands it back. For PADI, and most other agencies, buddy breathing is no longer a required certification skill, but some students may encounter divers who have learned to buddy breathe during a diving course in the past. As alternate air source regulators are required diving gear, buddy breathing is only necessary when a diver's alternate air source regulator has failed.

A Buddy Breathing Ascent seems likes it should be safer than an Emergency Swimming Ascent, but buddy breathing is a complicated procedure requiring good coordination and stress management between team members. Consider a hypothetical series of events leading up to a situation in which a Buddy Breathing Ascent is necessary and the reason that it is no longer a recommend ascent technique becomes clear:

A diver runs out of air. In general, a diver discovers that he is out-of-air after exhaling his final breath and attempting to inhale against an empty tank. He is already starved for air as he alerts his buddy and attempts to secure his buddy's alternate air source. When alerted to the emergency, his buddy may stare at him in wide-eyed disbelief for a few moments before helping. Out-of-air situations are rare and surprising. The out-of-air diver then reaches for the buddy's alternate air source, puts it in his mouth, and attempts to inhales a much-needed breath. The alternate air source doesn't work.
How likely is it that when the buddy hands the out-of-air diver his own primary regulator, the out-of-air diver will calmly take two breaths and hand it right back? The diver who is out of air must keep his airway open while the other diver is breathing because they are ascending and to hold his breath would risk a lung barotrauma. In a panic situation correct execution of this skill is unlikely for the casual recreational diver.

A Buddy Breathing Ascent not only requires each diver to remove the regulator repeatedly—putting each diver at risk of drowning—it requires the divers to do so while ascending together in a coordinated manner while maintaining a safe ascent rate. Buddy breathing works best when performed with a familiar buddy with whom it has been practiced to the point that it is automatic.

Choosing the Appropriate Emergency Ascent

In an out-of-air/low-on-air situation, a diver must choose the appropriate emergency ascent procedure for the circumstances of his dive. Understanding the differences among the standard emergency ascent procedures and the risks involved with each one will help a diver to react correctly in the unlikely event of an emergency.