Human Factors in CCR Diving
Closed-Circuit Rebreathers have transformed the boundaries of what divers can explore. They allow for longer bottom times, deeper exposures, quieter approaches, and missions previously unreachable on open circuit. To some, CCRs seem like highly advanced gear; to others, almost magical. But anyone who studies real accident patterns quickly learns the truth: the machine is rarely the main failure point.
CCR diving is often described as “gear-intensive,” and that’s true. We rely on redundancy,electronics, oxygen cells, solenoids, scrubber chemistry, and life-support engineering. Yet accident analyses from training agencies, DAN reports, and community investigations show the same recurring theme — most tragedies can be traced back to human behavior, not hardware malfunction. CCR diving amplifies the cognitive, emotional, psychological, and behavioral elements that influence how we make decisions underwater. It reveals weaknesses that are easy to ignore on open circuit but impossible to hide on a machine that demands constant awareness.
Below is a deeper, more integrative look at the human-factor challenges that shape CCR safety.
Complacency: Familiarity That Disguises Risk
The more hours a diver spends on a CCR, the stronger the illusion of mastery becomes. With routine comes comfort, and with comfort, the temptation to cut corners and slip into “automatic mode.” Many accidents begin long before anyone enters the water. You’ve dived the unit a hundreds times — you think you know every sound, every button, every sensation. That familiarity creates a dangerous illusion: the belief that “nothing will go wrong today.”
Complacency expresses itself subtly: a shortened checklist, a rushed pre-breathe, an assumption that the unit is “fine because it was fine yesterday”, and yesterday’s configuration guarantees today’s safety. But rebreathers only respond to precision. When complacency slips in, the unit becomes unforgiving.
Time Pressure and Task Loading
One of the strongest human-factor triggers is time pressure. The boat is waiting, the group is ready before you, or a photographer is eager to catch the perfect lighting, you’re already geared up and “don’t want to be the person who delays everyone. These external pressures reduce cognitive capacity and push divers into shortcuts.
On CCR, rushing often leads to unattached MAV hoses, incorrect scrubber packing, not noticing a closed oxygen cylinder, jumping without verifying setpoint…
Task loading intensifies this effect even further. Managing a camera, scooter, lights, shot lists, or navigation responsibilities competes directly with life-support monitoring. Many CCR incidents occur because attention was spent elsewhere at the wrong moment — often just long enough for PO₂ to drift into unsafe territory.
The Psychology of Confirmation Bias
Divers are naturally inclined to believe what they want to be true. This deeply human bias can be fatal on a rebreather.
Examples:
• You believe the unit is functioning well → ignoring a fluctuating PO₂
• You think your scrubber should last 400 minutes → denying symptoms of breakthrough at 350 minutes
• You assume bubbles are coming from the wing, not a counterlung
Once a diver forms an expectation, the mind selectively filters information to support that belief. Many CCR accidents begin with a diver noticing something subtle — and then explaining it away. Human factors training exists largely to help divers recognize and interrupt this pattern.
CO₂ Ignorance & Denied
One of the most lethal human-factor traps in CCR diving is underestimating CO₂ exposure. The early symptoms like anxiety, warmth, headache, slight confusion are easy to blame on poor sleep, stress, exertion, dehydration, or narcosis. Divers often push through these sensations because stopping the dive feels like inconvenience to the team.
But CO₂ issues rarely resolve themselves. The longer a diver delays acknowledging the symptoms, the smaller their margin for recovery becomes. Recognizing and acting on CO₂ exposure requires not only technical knowledge, but emotional honesty and discipline. It is a crucial behavioral skill.
Tunnel Vision (Perceptual Narrowing)
Under stress, humans lose access to their full sensory field. Vision narrows, sound dulls, and the ability to process multiple pieces of information at once collapses. On CCR, this means PO₂ checks, HUD signals, depth readings, and environmental cues can vanish from conscious awareness the moment a problem — even a small one — steals focus.
This is not a sign of poor training; it is human biology. Overcoming it requires practice, scenario drills, and the ability to slow thinking under pressure — skills that need to be cultivated intentionally, not assumed.
Team Behavior and Communication
CCR divers often operate like independent units even when diving in a team. Assumptions replace explicit communication. A diver notices discomfort but stays silent. Someone is unsure about a reading but does not want to delay the group. Another assumes the team will “catch” any mistake.
High-functioning CCR teams break this pattern. They speak clearly, verify openly, and treat communication as a skill, not a courtesy. They remove ego from team dynamics and encourage honesty, even when it disrupts the plan. Good team behavior is a human-factor competency (not a technical one).
Overconfidence, Ego, and the Illusion of Mastery
Technical divers often take pride in competence, certifications, and experience. That confidence becomes a hazard when it turns into ego. Ego-driven divers push the divebeyond recent experience, ignore personal red flags, skipping bailout or decompression planning, dismissing concerns from teammates, or refusing to call the dive. Ego thrives on comfort.
Cognitive Load from Filming or Exploration
For divers who film or document, human factors become even more critical. Cameras created distraction, narrow attention, create gear-related stress, alter movement and buoyancy, increase breathing effort, and monopolize mental space. When the focus narrows to framing, lighting, or movement, loop awareness fades.
Rebreathers require constant attention. When a diver prioritizes the camera over the PO₂, the unit continues to function — until it doesn’t.
Physical State: The Invisible Variable
Fatigue, hydration, stress, and physical condition influence decision-making far more than most divers admit.
Fatigue slows cognitive response.
Dehydration increases CO₂ retention.
Anxiety alters breathing patterns.
Lack of sleep reduces awareness and reaction time.
These factors are rarely considered “technical,” but they profoundly affect human performance on CCR.
Culture, Peer Pressure, and Group Dynamics
Humans are social creatures. Even experienced divers underestimate how strongly group culture influences choices:
These seemingly small pressures are powerful contributors to incident chains. Learning to recognize and resist them is essential.
Conclusion:
Why Human Factors Matter More Than Mechanics**
CCR units are engineering masterpieces, but they are still machines. They do not rush, skip steps, feel embarrassed, get distracted, or reinterpret warnings. Humans do.
This is why human-factor competence is the real foundation of safe, long-term diving.
In the end, it is not the rebreather that determines the safety of the dive.
It is the diver’s mind.
