Understanding decompression sickness and how to stay safe after ascent

Which condition is caused by pressure changes during ascent?

• A. Pulmonary embolism
• B. Lung rupture
• C. Barotrauma
• D. Decompression sickness

Answer: (D)

Decompression sickness, often referred to as "the bends," occurs when a diver ascends too quickly, causing dissolved gases (primarily nitrogen) in the body to come out of solution and form bubbles. When a diver is underwater, the pressure is higher, and gases are more soluble in bodily fluids. Upon ascent, the pressure decreases rapidly, leading to a situation where the gases expand and can create bubbles within tissues and the bloodstream. This condition can result in various symptoms depending on where the bubbles form and their impact on the body, ranging from joint and muscle pain to more serious complications such as paralysis or unconsciousness. Preventative measures, such as ascending slowly and performing safety stops, are crucial in avoiding decompression sickness during diving activities. While other conditions like pulmonary embolism, lung rupture, and barotrauma may relate to pressure changes, they do not specifically describe the series of events and physiological implications associated with the rapid ascent that leads to decompression sickness.

Why the Bends Happen: Decompression Sickness and Open Water Safety

If you’ve ever surfaced from a long swim and felt a dull ache in a joint, or a bit of numbness that wasn’t there before, you’re not imagining things. Those sensations can be a sign of decompression sickness—often nicknamed “the bends.” It’s one of those topics that sounds technical, but it’s really about how our bodies react to pressure changes when we ascend. For anyone exploring the IANTD Open Water Diver path, understanding this condition is a cornerstone of safe, confident diving.

What is decompression sickness, really?

Let me explain it in plain terms. When you’re underwater, the surrounding water pressurizes your body. That pressure makes gases—mostly nitrogen—dissolve in your blood and tissues more than they would at the surface. It’s a bit like a sponge soaking up water when you squeeze it.

Now, when you start to ascend, the water pressure around you drops. If you rise slowly and stop at safe depths, your body has time to off-gas those dissolved nitrogen bubbles gradually. But if you go up too fast, the dissolved gases come out of solution too quickly and form tiny bubbles in tissues and in the bloodstream. That is decompression sickness.

Here’s the thing: the bubbles don’t just stay in one place. Depending on where they form, they can interfere with nerves, joints, lungs, skin, or the brain. That’s why DCS has a range of symptoms, from achy joints to numbness, to more serious signs like dizziness, confusion, or weakness.

The science you don’t have to hate

I won’t drown you in physics, but a quick, practical frame helps. Under pressure, more gas stays dissolved in your liquids. As pressure declines, those gases want to come out of solution. If that happens too fast, you get bubbles. You don’t need to be a chemist to get the core idea: slow, deliberate ascent gives your body a chance to safely vent the excess gas.

This isn’t about “tricking” the system; it’s about respecting how your body handles gases when mid-water, pressure, temperature, and exertion all push you in different directions. The result is why the safety stops you hear about aren’t optional decorations—they’re part of the plan your instructor (and your dive computer) will emphasize.

Spotting the signs: what to watch for

Decompression sickness can be sneaky because early symptoms can mimic tiredness after a long dive or a familiar post-dive ache. The key is to connect the dots and act quickly if they show up after ascent.

Common symptoms include:

• Joint and muscle pain, especially after a longer or deeper dive

• Tingling, numbness, or a “pins and needles” feeling

• Dizziness, balance problems, or confusion

• Fatigue or a sense of weakness

• A skin itch or a mottled rash

• In severe cases, numbness or weakness of limbs, trouble speaking, or paralysis

The onset time can vary from minutes to hours after surfacing, which is why staying alert after a dive is smart. If symptoms appear, it’s not something you can brush off—treatment needs to start promptly.

Barotrauma, embolisms, and the other pressure cousins

You’ll hear about a few other pressure-related issues, and it’s helpful to keep them straight. Pulmonary embolism and lung rupture are serious medical problems, but they’re not the same process as decompression sickness. A pulmonary embolism is a blood-clot issue that can be life-threatening, while barotrauma refers to injury from pressure changes that affect air spaces (like the ears, sinuses, or lungs) during ascent or descent, typically due to blocked or maladjusted pressure equalization. Barotrauma is common in people who don’t equalize softly and steadily, but it isn’t the same mechanism as nitrogen bubbles forming in tissues and blood.

So, when you’re asked on a test or just discussing it with fellow divers: DCS is about rapid ascent and gas coming out of solution; barotrauma is about pressure harming air spaces; emboli and lung rupture have different origins. The key takeaway for safety is that decompression sickness is the direct result of pressure changes during ascent and is specifically about gas coming out of solution and forming bubbles.

Prevention: how to stay out of trouble

The old saying “slow and steady wins the race” applies here, with a dive-focused twist.

• Ascend gradually. The most practical rule is to avoid rapid ascents. If you’re using a dive computer or tables, follow the profile your plan requires.

• Do a safety stop. A common recommendation is a stop at around 5 meters (15 feet) for 3 to 5 minutes, though deeper or longer may be advised depending on the dive. This pause lets your body off-gas gradually and reduces bubble formation.

• Plan for depth and time. Sticking to a conservative plan, especially after long or deep dives, is wise. If you notice your computer suggesting longer safety stops or shorter bottom times, respect that guidance.

• Stay hydrated and avoid exerting yourself excessively at the end of a dive. Fatigue, dehydration, and cold can amplify risk.

• Use reliable gear and a good computer. Modern dive computers, Nitrogen-loading indicators, and well-maintained regulators give you real-time feedback on ascent rates and decompression obligations. Brands like Suunto, Garmin, and Shearwater are common in the community, and they’re only as good as the plan you follow.

• Dive within your training. For the IANTD Open Water Diver path, the emphasis on gradual ascent, safety stops, and awareness of symptoms isn’t just academic—it’s your daily safety toolkit in water.

If symptoms develop after a dive, act quickly

Treatment is time-sensitive. If you or a buddy notice any DCS symptoms after surfacing, here’s what to do:

• Stop and stay calm. Don’t continue to descend or re-ascend aggressively.

• Breathe fresh air or, ideally, 100% oxygen if available. Oxygen helps wash out nitrogen from the body.

• Seek medical help immediately. Decompression sickness is a medical emergency. A recompression treatment in a hyperbaric chamber is usually the recommended course of action.

• Do not fly soon after a suspected DCS episode. Flying increases pressure changes in the body and can worsen symptoms; medical teams will advise on when it’s safe to fly.

• Share dive details with responders: depth, bottom time, ascent rate, any stops, symptoms, and the time they began. This information helps clinicians decide quickly on treatment.

A practical analogy to keep in mind

Think of your body as a soda bottle under pressure. When you’re deep, the fizz is calm—everything’s dissolved nicely. If you yank the cap, the fizz erupts. That eruption is your bubbles trying to escape, and if it happens too fast, you end up with a fizzy mess in the wrong places. Gentle, controlled releases prevent the eruption from spilling over your hands and neck—exactly what the safety stops and ascent rates aim to do for your body.

Putting this into the IANTD Open Water Diver context

Here’s the core takeaway you’ll want to carry into your next water session: decompression sickness is the consequence of rapid ascent and improper off-gassing of dissolved nitrogen. It’s not the only pressure-related concern you’ll encounter, but it’s the one most closely tied to ascent speed and safety stops.

A few quick reminders you can carry in your pocket:

• DCS = bubbles forming in tissues/blood due to rapid ascent and pressure drop.

• Symptoms vary; some show up right away, others later.

• Prevention is practical: slow ascent, safety stops, conservative planning, stay hydrated, and monitor your computer.

• If symptoms appear, treat as a medical emergency and seek hyperbaric care.

A final thought: learning to respect pressure isn’t about fear; it’s about confidence. The ocean is a dynamic, generous teacher, but it rewards preparation and patience. As you practice with your open water skills and build your experience, you’ll naturally adopt smoother ascents, better control, and a clearer sense of when to pause and breathe. That calm, methodical approach doesn’t just reduce risk—it enhances every dive by letting you and your buddy stay in the moment, exploring with curiosity rather than worry.

If you ever find yourself explaining this to a friend or a fellow student, you’ll have a clear, human way to describe it: decompression sickness happens when you rush back to the surface and the nitrogen that was comfortable under pressure refuses to stay put. The cure is time, oxygen, and a trained medical team if symptoms appear. In the long run, that knowledge pays off in safer days on the water and more confident, enjoyable adventures beneath the surface.