Decompression Sickness Explained
When you go deeper underwater, pressure increases. At 30 meters, you're breathing air at roughly four times the surface pressure. Your body absorbs more nitrogen into your tissues the longer you stay down. When you ascend too quickly, that dissolved nitrogen comes out of solution and forms bubbles. That is what causes the bends. It is technically called decompression sickness, or DCS. The most common symptom is joint pain, usually in the shoulders, elbows, or knees. People call it the bends because the pain is so severe divers instinctively curl up into a fetal position. But DCS isn't just joint pain. Type 1 DCS involves milder symptoms: skin rash, itching, fatigue, and swelling. Type 2 DCS is serious and neurological. It can cause paralysis, loss of bladder control, confusion, or death if untreated. I have seen both in my time. Here is the thing nobody tells you at Open Water class: the bends doesn't always hit you right after you surface. Symptoms can be delayed by anywhere from 15 minutes to 12 hours. I learned this the hard way on a trip to the Red Sea. We did a bunch of dives on mixed gas on one weekend, and I felt fine coming up from a 42-meter wall dive. Next morning, I woke up with a sharp pain in my left shoulder and tingling in my fingers. I was on a boat in Egypt. The nearest recompression chamber was a two-hour drive away. We spent the entire day moving as little as possible, keeping the diver horizontal, and administering 100% oxygen from our first-aid kit. By late afternoon the tingling had stopped. The shoulder pain stuck around for two more days. If we had waited until the evening to evacuate, the outcome could have been very different.
There are a few misconceptions worth clearing up. First, fitness has almost nothing to do with your risk of DCS. I have seen marathon swimmers get the bends and overweight desk workers come back fine. The variables are depth, time, ascent rate, and how many dives you do in a row. Second, dehydration makes it worse. If you show up to a dive trip mildly dehydrated, your blood is more viscous and nitrogen elimination slows down. Drink water before and between dives. It sounds basic, but most people skip it.
How It Actually Works
Your body has different tissue compartments that absorb and release nitrogen at different rates. Fast tissues like blood and brain take up and off-gas nitrogen quickly. Slow tissues like fat and connective tissue take much longer. This is why repetitive dives are risky. On your second dive of the day, your fast tissues still haven't cleared the nitrogen from the first dive. You're starting with a residual load. That is why no-decompression limits get shorter with each successive dive, and why dive computers calculate this in real time. The old tabletop method, published by the US Navy, is still the foundation. But modern dive computers use modified algorithms, typically Bühlmann ZH-L16 with gradient factors. The original Bühlmann model was conservative enough for military diving with mixed gases, but recreational computers added safety margins. Gradient factors let you dial how conservative you want to be. A low-gradient-factor dive stops more often and stays closer to the no-decompression limit. High gradient factors mean you're pushing closer to the edge. Both work. Neither prevents DCS if you ignore your computer and fly too soon after diving. Here is the counter-intuitive part: shallow dives can give you DCS too. A lot of people think only deep dives cause decompression sickness. They cruise along at six meters for forty-five minutes and feel invincible. But if your ascent is sloppy, or if you are doing multiple dives in a row, shallow depths still build nitrogen load. I tracked a diver once who got DCS from two repeated profiles at just eight meters, sixty minutes each, with eleven-minute surface intervals. His computer showed zero no-deco time used. He ignored it. He needed treatment in a hyperbaric chamber the next day.
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Prevention And What To Do If It Happens
The standard prevention is straightforward but people skip steps. Stay within your no-decompression limits. Ascend no faster than nine meters per minute, which is about the speed of your smallest exhaled bubbles. Do a safety stop at five meters for three minutes on every dive. Don't skip it. Make sure your dive computer battery is fresh and it is calibrated. Check your gear before every trip because a faulty barometer or a lagging depth sensor will give you bad numbers, and bad numbers get people hurt. If you suspect DCS after a dive, the protocol is non-negotiable. Get the affected person on 100% oxygen immediately. Keep them lying flat, ideally on their left side if they are conscious. Hydrate with water if they are fully alert. Do not give them anything by mouth if they are confused or vomiting. Contact DAN or the local emergency number and arrange evacuation to the nearest hyperbaric chamber. Do not fly them commercially. Do not let them fly in a private plane unless the cabin is pressurized to sea level. If neither is possible, call DAN's 24-hour advisory line. They can help you locate treatment facilities and guide you through onboard stabilization. Hyperbaric oxygen therapy works by increasing ambient pressure, which shrinks the bubbles, and flooding the tissues with oxygen, which accelerates nitrogen washout. The US Navy Treatment Table 6 is the standard for Type 2 DCS. It takes roughly six to seven hours. Treatment Table 5 is faster and used for milder cases. Neither is something you can DIY. This is a medical emergency, not a wait-and-see situation. The window for effective treatment narrows significantly after the first six to twelve hours.
One more practical note. Some dive shops now offer on-site recompression chambers, especially in popular wreck diving destinations like the Red Sea or the Caribbean. If you are planning a technical or repeat-dive trip, check whether your destination has a working chamber. It saved my buddy once in Dahab when he developed abdominal DCS after a dive to the Blue Hole. The chamber on-site brought him back to full function in under four hours. Without it, we would have been looking at a medevac that took two full days to arrange. Know your options before you go, not after.
