· safety · 4 min read
DCS in Freediving: The Risk Most Freedivers Ignore
Blackout gets most of the attention, but deep or repetitive freediving can also create decompression stress. DCS/DCI is rare in freediving, but neurological symptoms after a dive are an emergency.
Most freedivers are taught to respect blackout. Good. They should.
But deep or repetitive breath-hold diving carries another rare, serious risk: decompression sickness (DCS), often discussed in freedivers under the broader term decompression illness (DCI).
This article is general safety education, not medical advice. If a diver has neurological symptoms after diving, treat it as an emergency.
What Is DCS?
DCS happens when pressure changes allow dissolved gas, mainly nitrogen, to form bubbles in body tissues or blood. At depth, pressure is higher, so more nitrogen can dissolve. During ascent, pressure drops. If gas comes out too quickly, bubbles can irritate tissues, block blood flow, and trigger neurological or systemic symptoms.
In freediving, clinicians often use DCI rather than DCS. After breath-hold dives, similar symptoms may come from nitrogen bubbles, arterial gas embolism, lung barotrauma, or mixed mechanisms. Exact cause is not always clear at the surface.
Simple version:
Deep dives, repeated often, with short surface rests, create more decompression stress.
”But Freedivers Don’t Breathe Compressed Air”
True. Freedivers do not breathe extra gas at depth like scuba divers, so everyday shallow recreational freediving is not the same risk.
But documented breath-hold DCS/DCI exists. It usually appears when the dive profile stacks several stressors:
- Repeated dives.
- Deep dives.
- Short surface intervals.
- Long dive sessions.
- Fast ascents or assisted ascents.
- Lung squeeze or possible barotrauma.
- Advanced practices like packing.
- Commercial, spearfishing, competitive, or extreme-depth profiles.
So “I don’t use scuba” lowers risk. It does not make DCS impossible.
When Risk Starts To Matter
No single depth or surface interval makes DCS impossible. Concern rises when a dive day begins to look like this:
- Repeated dives to 20-40 m over several hours.
- Surface rests shorter than the dives.
- Long sessions full of “one more dive” decisions.
- Fast ascents, assisted ascents, scooter/sled use, or aggressive depth progression.
- Packing, lung squeeze symptoms, or suspected barotrauma.
- Any neurological symptoms after diving: numbness, weakness, dizziness, slurred speech, visual change, confusion, severe headache, balance trouble, or unusual fatigue.
Extreme single dives also matter. Models based on documented breath-hold dives suggest single-dive DCS risk stays low until roughly 100 m, then rises sharply at extreme depths. That does not make 100 m safe. It only describes elite single-dive modelling, not repeated training days.
Case Studies
Case 1: Classic Repeated-Dive DCS
Paulev reported DCS after repeated breath-hold dives to 15-20 m. The profile involved about 60 dives over roughly 5 hours, with surface rests from seconds to 1-2 minutes.
Key lesson: moderate depth can become risky when repeated many times with little recovery.
Case 2: Spearfishing Champion, 30-35 m
Cortegiani et al. reported Taravana syndrome in an underwater fishing champion. He did 19 dives to 30-35 m over 150 minutes. Each dive lasted about 2:10-2:50, with only 1:00-1:30 at the surface.
Symptoms included dizziness, numbness, blurred vision, and head pain. They improved, then returned the next day with seizure and loss of consciousness. Hyperbaric oxygen helped.
Key lesson: symptoms can fade, then return. Do not “wait and see” after neurological signs.
Case 3: Ama Commercial Diver
Kohshi et al. reported a 65-year-old Ama diver doing repetitive 10-20 m working dives. On fourth successive dive day, he developed slurred speech, hand numbness, and gait problems. MRI showed brain lesions. Oxygen and hyperbaric therapy were used.
Key lesson: long-term experience does not erase risk.
Case 4: Modern Freediver Survey
Yu et al. surveyed breath-hold divers who reported DCI events. Many were trained divers. Reported contributors included depth, short surface intervals, and pulmonary barotrauma. Common symptoms included weakness, numbness, slurred speech, and fatigue.
Key lesson: “within my limits” does not always mean “no DCI risk.”
How To Prevent DCS
Best prevention is boring. Boring keeps divers alive.
- Keep surface intervals generous, especially as depth and repetition increase.
- Avoid deep repetitive dive sessions with short rests.
- Do fewer deep dives, not “one more because I feel good.”
- Build depth slowly with trained supervision.
- Avoid packing unless advanced, trained, and supervised.
- Avoid scooter-assisted depth or rapid ascents without expert planning.
- Stop diving if you get chest symptoms, cough blood, unusual breathlessness, neuro symptoms, or “something is wrong” feeling.
- Do not combine scuba and freediving casually on same day without proper dive-medicine guidance.
- Have oxygen available for deep/repetitive training days.
- Know nearest emergency and hyperbaric contact.
- If neurological symptoms appear after freediving: stop diving, give emergency oxygen if available, and call emergency services, DAN, or hyperbaric support.
Takeaway
DCS in freediving is rare, but real. For most beginners, blackout is usually the bigger day-to-day risk. For deep, repetitive, competitive, spearfishing, or commercial profiles, decompression stress belongs in the safety plan.
Rule of thumb:
One shallow fun dive? DCS is unlikely. Many deeper dives with short rests? Respect decompression stress. Neurological symptoms after diving? Emergency.
Sources
Blogg 2023 systematic review, Lemaitre 2009 review, Paulev 1965, Cortegiani 2013, Kohshi 2020/2021, Yu 2025.