Understanding the 80-foot, 60-minute submersion: why a 1 minute at 20 feet and 28 minutes at 15 feet matters for a safe ascent

What is the designated decompression requirement for a dive to 80 feet for 60 minutes?

• A. No decompression required
• B. 1 minute at 30 feet, 15 minutes at 20 feet
• C. 1 minute at 20 feet, 28 minutes at 15 feet
• D. 2 minutes at 10 feet, 20 minutes at 15 feet

Answer: (C)

The correct response highlights the importance of managing nitrogen absorption and off-gassing during dives, particularly for a dive of this depth and duration. When a diver spends 60 minutes at 80 feet, they are likely to exceed the no-decompression limits set for recreational diving, which makes decompression necessary to avoid nitrogen narcosis and decompression sickness. Option C specifies a requirement of 1 minute at 20 feet followed by 28 minutes at 15 feet. This approach allows the diver adequate time to safely off-gas the absorbed nitrogen from the body. Ascending to 20 feet first helps to minimize pressure quickly, while the extended time at 15 feet further ensures that nitrogen levels are reduced to safe levels before reaching the surface. In contrast, the other responses do not effectively address the necessary procedures after such a prolonged dive. Some suggest insufficient decompression time or put forth a sequence of depths and durations that are not suitable for safe ascent after a dive of this length, thereby increasing the risk of decompression sickness. Proper understanding of decompression schedules and adhering to them is crucial for diver safety, which is why Option C is the most appropriate choice.

Decompression math under the surface: why 1 minute at 20 feet and 28 minutes at 15 feet makes sense

Here’s the thing about underwater time at depth: nitrogen from your breathing gas dissolves into your tissues the deeper and longer you stay. The longer you stay, the more nitrogen builds up. The deeper you go, the faster that nitrogen soaks in. When you finally start moving back toward the surface, your body has to shed that nitrogen slowly, otherwise you risk decompression sickness. That’s why, for a long, deep outing, a planned ascent with staged pauses is essential, not optional. It’s about safety, yes, but also about feeling steady and confident as you close in on the surface.

What happens when you’re at 80 feet for an hour

Imagine you’re at 80 feet (about 24 meters) for an hour. At that depth, you’re facing a lot more pressure than at the surface, and your body absorbs nitrogen more quickly. Recreational no-decompression limits (NDLs) are the maximum bottom times you can spend at a given depth without needing mandatory decompression stops on the ascent. When you push a long bottom time like 60 minutes at 80 feet, you’re almost certainly beyond the NDL for a recreational profile. In plain terms: without pauses, you’d be diving into a zone where the nitrogen your body has absorbed could cause problems on the way up.

That’s where the decompression schedule comes in. A staged ascent lets your body off-gas nitrogen gradually, reducing the risk of decompression sickness. Think of it as giving your tissues a gentle, safe “thank you” for all that nitrogen they’ve held onto while you explored the underwater world. The important bits are the choices of depth for the stops and the duration of each stop. They’re not arbitrary; they’re designed to balance time, safety, and the practical realities of a long outing.

Why option C stands out: 1 minute at 20 feet, then 28 minutes at 15 feet

The correct decompression response for a 60-minute outing at 80 feet is 1 minute at 20 feet followed by 28 minutes at 15 feet. This plan accomplishes two crucial things at once:

• First, a quick, shallow pause at 20 feet gives your body an early, partial release of absorbed nitrogen. It’s like taking the edge off early in the ascent, before nitrogen levels become a bigger issue as you rise higher.

• Second, the longer stretch at 15 feet keeps the off-gassing active as you approach the surface. This extended period at a relatively mild pressure is where most of the nitrogen is safely released and brought back down to safer levels by the time you reach the shallows.

Ascending to 20 feet first helps a lot. It reduces the pressure quickly enough to initiate off-gassing, but not so fast that you lose control of your ascent. Then, spending 28 minutes at 15 feet lets nitrogen drop to safer amounts in a controlled way. This combination works well for a 60-minute stint at a significant depth, where an all-at-once return to the surface would be reckless.

A quick mental model helps here, too. Think of your nitrogen load like a jar of water. The deeper you are, the more water pours in. You can let some water out at 20 feet, but you still need a longer, slower release at 15 feet to finish emptying the jar. The 1-minute–at–20-feet plus 28-minute–at–15-feet sequence is a straightforward way to manage that release without rushing or under-stressing your system.

Why the other options aren’t as safe or practical for this scenario

• Option A: No decompression required. For a 60-minute outing at 80 feet, this is optimistic to the point of risk. The bottom line is that staying down that long at that depth puts you into a zone where a no-stop ascent isn’t realistic for safe off-gassing. It sounds simple, but the science says otherwise: your nitrogen load would be higher than what a no-decompression plan can safely handle.

• Option B: 1 minute at 30 feet, 15 minutes at 20 feet. This path starts too deep to be ideal for an initial stop, and the total time at shallow stops is likely insufficient to safely shed the nitrogen after a long bottom time. The deeper first stop doesn’t help as much as a shallow, early release would, and the shorter total off-gassing window at 20 feet doesn’t give enough time for the body to get to a truly safer state before surfacing.

• Option D: 2 minutes at 10 feet, 20 minutes at 15 feet. Though the 15-foot stop is decent, the 2 minutes at 10 feet is a bit of a misfire. It doesn’t provide a meaningful early release compared to the shorter, shallower pause at 20 feet used in Option C. The overall time at depth after the bottom portion isn’t enough to ensure a comfortable, safe ascent for this particular bottom time.

The key takeaway here is: decompression isn’t just about time; it’s about the right balance of depths and durations to let your body off-gas nitrogen in a controlled manner. Option C hits that balance for an 80-foot, hour-long outing.

Practical notes that help the idea land

• Decompression stops aren’t negotiable on longer, deeper outings. They’re part of a disciplined approach to safety, and they’re built into how conservative planning is done in many training frameworks. If you’re planning a real-world outing that’s long and deep, you’ll either use a dive computer that guides you or follow a table-based plan created by a reputable instructor or agency.

• The actual numbers you see in planning tools are informed by gas mixtures, surface intervals, and your individual physiology. People burn through nitrogen a little differently, so personal experience matters. That’s why training emphasizes staying within planned stops and being willing to adjust the plan if you feel off-gas symptoms or if practical conditions change.

• A shallow-stop habit can be a lifesaver. Even if you aren’t required to pause, many divers opt for a short safety stop around 15 feet for a couple of minutes as they ascend to the surface. It’s a small, sometimes overlooked habit with big safety dividends.

• Equipment and ergonomics matter. A reliable depth gauge, a good dive computer, and properly maintained gear reduce cognitive load while you’re charting a careful ascent. Modern computers are especially helpful because they tailor decompression needs to real-time depth and ascent rate, but a solid backup plan is always wise.

• The human factor. You’re not just calculating numbers; you’re listening to your body. If you feel lightheaded, tingly, or unusually fatigated, that’s a sign to slow down and reassess. The goal isn’t just following a schedule; it’s staying safe and comfortable while you enjoy the underwater world.

A few more angles that often come up in real-world thinking

• Nitrogen narcosis versus decompression sickness. Narcosis tends to be a concern at depth, especially as you breathe more nitrogen under pressure. It’s a separate sensory issue from decompression sickness, but both are tied to how nitrogen behaves under pressure. The decompression stops help reduce the risk of DCS after the nitrogen has done its job soaking into tissues.

• Experience and planning go hand in hand. The more you know about how your body responds to depth, the better you’ll be at recognizing when a schedule makes sense for you. This is one of those areas where training and lived experience align to keep you safe.

• The broader point: why a staged approach matters. Even outside the specific numbers, the logic stays the same. You want to shift from deep, high-pressure environments to shallower ones gradually, letting your tissues shed nitrogen at a rate your body can handle. It’s about control, not speed.

What to carry in your thinking as you head to the water

• Confidence in a plan. If you’re going to push toward long or deep outings, you’ll want a clear plan that includes scheduled pauses. It’s not about fear; it’s about respect for the physics of your body under pressure.

• Flexibility. Real-world conditions—currents, visibility, fitness, and gas supply—affect your plan. Being able to adjust, while keeping the core idea of safe off-gassing intact, is the mark of a seasoned underwater traveler.

• Learning from the numbers. The specific schedule in Option C—1 minute at 20 feet, 28 minutes at 15 feet—serves as a concrete example of how staged decompression can function. It’s a model to help you think about similar situations and how to apply the same logic to other depths and times.

Bottom line

For a 60-minute outing at 80 feet, a decompression schedule like 1 minute at 20 feet, followed by 28 minutes at 15 feet, is a thoughtful approach to managing nitrogen buildup. It’s not about checking boxes; it’s about making the ascent safer and more predictable. The alternative options either underestimate the time needed to off-gas or misplace stops in a way that wouldn’t serve the body as effectively.

Next time you’re mapping a long underwater adventure, keep the thread of decompression in mind. The surface is inviting, sure, but getting there with a calm, well-planned ascent—that’s what lets you carry the story of the day with you, instead of a wrenching reminder of what could have happened. After all, the ocean isn’t going anywhere. Your safety and enjoyment shouldn’t be rushed. Take the time you need to rise thoughtfully, and you’ll return with stories—yes, and with pride in having respected the science that keeps you above water.