The bends, or decompression sickness, happens when nitrogen gas dissolved in your blood and tissues forms bubbles as you ascend from a dive. Preventing it comes down to controlling how fast you surface, how long you stay at depth, and what you do before and after your dive. Most cases are avoidable with proper planning and discipline underwater.
Why Nitrogen Bubbles Form
When you descend underwater, the increasing pressure forces nitrogen from your breathing gas to dissolve into your blood and tissues. The deeper you go and the longer you stay, the more nitrogen saturates your body. This is completely normal and harmless while you’re at depth.
The problem starts when you ascend. As pressure drops, that dissolved nitrogen wants to return to gas form. If you rise slowly enough, the nitrogen travels through your bloodstream to your lungs and gets exhaled harmlessly. If you ascend too quickly, the nitrogen comes out of solution faster than your body can clear it, forming bubbles in your blood and tissues. These bubbles likely grow from tiny pre-existing gas nuclei attached to blood vessel walls, where they expand and break free into the bloodstream. The result can range from joint pain and skin rashes to paralysis and life-threatening cardiovascular collapse.
Ascend Slowly
Your ascent rate is the single most important factor you control. The U.S. Navy and NOAA recommend ascending no faster than 30 feet per minute. Recreational dive training agencies allow rates between 30 and 60 feet per minute, though the trend has moved toward the slower end. For perspective, 30 feet per minute is roughly one foot every two seconds, which feels almost uncomfortably slow when you’re in the water. That slowness is the point.
A practical way to gauge your speed: rise no faster than your smallest exhaled bubbles. If you’re passing your own bubbles on the way up, you’re going too fast.
Make Safety Stops Standard Practice
A safety stop is a deliberate pause during your ascent, typically at 15 to 20 feet for three to five minutes. During this time, your body continues offgassing nitrogen at a depth where bubble formation is unlikely. Safety stops should be treated as standard procedure on every dive below 33 feet, not as something optional you do only when you’ve pushed your limits.
The most effective approach for reducing post-dive bubble formation combines three elements: an ascent rate of 30 feet per minute, a deep stop at roughly half your maximum depth for about 2.5 minutes, and a final stop at 15 feet for three to five minutes. So if you dive to 100 feet, you’d pause at 50 feet for 2.5 minutes, continue ascending, then hold at 15 to 20 feet for three to five minutes before surfacing. This layered approach gives your body multiple opportunities to clear nitrogen safely.
Respect No-Decompression Limits
Every depth has a maximum time you can stay and still ascend directly (with safety stops) without mandatory decompression. These no-decompression limits are published in dive tables and programmed into dive computers. Exceeding them means your body has absorbed so much nitrogen that a normal ascent isn’t safe, and you’d need extended stops at specific depths to avoid the bends.
Recreational divers should plan every dive to stay well within these limits, not right at the edge. Dive tables give you maximum allowable times, but those maximums assume everything else goes perfectly. Building in a margin of safety accounts for the many variables that tables can’t capture, like your hydration, fatigue, and individual physiology.
Use a Dive Computer
Dive computers track your depth and time continuously, calculating how much nitrogen your tissues have absorbed in real time. They model your body as a series of theoretical tissue compartments that absorb and release nitrogen at different rates. Some tissues (like blood) load and unload quickly, while others (like fat and cartilage) take hours.
Different manufacturers use different algorithms. Many computers use versions of the Bühlmann model, which tracks 16 tissue compartments with absorption half-times ranging up to 635 minutes. Others use the Reduced Gradient Bubble Model, which accounts for both dissolved gas and free gas bubbles. PADI’s Recreational Dive Planner is based on the DSAT model. Regardless of which algorithm your computer uses, the key is to follow its guidance, especially its ascent rate warnings and remaining no-decompression time.
A dive computer is more accurate than tables alone because it adjusts calculations based on your actual dive profile rather than assuming you spent the entire dive at maximum depth.
Plan Surface Intervals for Repetitive Dives
If you’re doing multiple dives in a day, the nitrogen left over from your first dive matters. Your body doesn’t fully offgas between dives unless you wait long enough. The U.S. Navy’s repetitive dive tables track residual nitrogen using letter group designations (A through Z), with each letter representing how much nitrogen remains in your tissues. The longer your surface interval, the more nitrogen you eliminate, and the lower your letter group drops before your next dive.
In practice, this means longer surface intervals let you stay deeper or longer on your next dive without exceeding safe limits. Shorter intervals mean you start your second dive already carrying a nitrogen load, so your allowable bottom time shrinks. Most dive computers handle this math automatically, carrying over residual nitrogen into the next dive’s calculations. A minimum surface interval of at least one hour is a reasonable guideline for recreational multi-dive days, though longer is always better.
Watch Your Body Composition and Hydration
Nitrogen is about five times more soluble in fat than in water-based tissues, which means body fat acts as a nitrogen sponge. A study of fisherman-divers in Mexico found that both the number and severity of decompression sickness events were associated with higher body mass index. Among the divers studied, over 42% were obese and nearly 29% were overweight, and those with higher BMIs experienced more frequent and more severe cases. Maintaining a healthy weight reduces the amount of nitrogen your body stores at depth and speeds up how quickly you offgas on ascent.
Dehydration thickens your blood, slowing circulation and making it harder for nitrogen to travel to your lungs for elimination. Drink plenty of water before and between dives, and limit alcohol the night before. Tropical dive destinations make this easy to forget, but showing up to a dive boat dehydrated meaningfully increases your risk.
Avoid Exercise During and After Diving
Strenuous physical activity during or immediately after a dive increases bubble formation. Exercise boosts circulation, which can mobilize nitrogen bubbles and interfere with the body’s ability to eliminate dissolved gas. Research published in The Journal of Physiology found that more bubbles were detected when subjects exercised during or immediately following decompression.
Interestingly, moderate exercise well before a dive (like a workout the day prior) may actually reduce bubble formation by altering the blood vessel lining where gas nuclei attach. But the timing matters enormously. The safe approach is to avoid heavy lifting, running, or vigorous swimming for several hours after your last dive. Keep your post-dive activity limited to walking, light stretching, and relaxing.
Wait Before Flying
Airplane cabins are pressurized to the equivalent of 6,000 to 8,000 feet altitude, which is lower pressure than sea level. Flying too soon after diving exposes your body to reduced pressure while nitrogen is still working its way out of your tissues, essentially creating the same conditions as a too-fast ascent.
Guidelines from the Undersea and Hyperbaric Medical Society are straightforward. After a single no-decompression dive with less than two hours total dive time in the previous 48 hours, wait at least 12 hours before flying. After multiple days of diving, wait at least 24 hours. If you made any dive requiring decompression stops, wait a minimum of 24 hours and preferably 48 hours. These intervals apply to any flight at cabin altitudes up to 8,000 feet, which covers virtually all commercial flights. When in doubt, add more time. Scheduling a rest day at the end of a dive trip before your flight home is one of the simplest and most effective precautions you can take.