Decompression sickness (DCS, "bends" / "caisson disease") occurs when nitrogen in body tissues comes out of solution as gas bubbles under decreasing ambient pressure (like opening a fizzy drink).
Mechanism
Under normal breathing nitrogen stays dissolved in tissue (Henry's law). Under rapid pressure reduction:
- Nitrogen cannot leave the body through the lungs fast enough.
- Gas bubbles form in blood, joints, nervous system.
- Bubbles block capillaries and damage tissue.
Risk for PPL pilots
| Scenario | Risk |
|---|---|
| Cruise in SEP below 10 000 ft | negligible |
| Climb above 18 000 ft in unpressurised cabin | elevated |
| Flying soon after diving | significantly elevated — see below |
| Rapid descent from high altitude | low |
Diving and flying — minimum wait times
Established guidance from DAN (Divers Alert Network), PADI and UK CAA — slightly conservative variations per organisation:
| Dive | Minimum wait before flying |
|---|---|
| Single no-decompression dive | at least 12 hours |
| Multiple dives or multi-day diving | at least 18 hours |
| Decompression dive | at least 24 hours |
These values apply to cabin altitudes up to 8 000 ft (typical airliners). Longer waits may be necessary for unpressurised SEPs operating in mountainous regions.
Symptoms
| Type | Symptoms |
|---|---|
| "Bends" (joints) | Joint pain, often shoulders and knees |
| "Chokes" (respiratory) | Chest pain, cough, dyspnoea |
| Neurological | Paralysis, vision disturbance, speech disorder, loss of consciousness |
| Cutaneous | Itching, skin rash |
Recovery
- Descend to the lowest possible altitude.
- Administer oxygen (100 %).
- Land immediately and contact a hyperbaric chamber (HBO therapy needed).
- During transport to the clinic: lying down, plenty of fluids.