nDeco Dive Planner Blog

All About Ascents: The Key to Safe Scuba Diving

A controlled ascent is one of the most important skills a diver can master. While descending too quickly can cause discomfort, ascending too fast can lead to serious risks like decompression sickness (DCS), lung overexpansion injuries, and rapid buoyancy changes.

Many divers rely on dive computers to regulate their ascent rates, but it’s crucial to understand the physics of pressure changes and how to control your ascent without a computer if necessary. In this article, we’ll explore the importance of ascent control, depth-specific ascent rates, and alternative ascent techniques for a safe return to the surface.

Why a Slow, Controlled Ascent Matters

As a diver ascends, the surrounding water pressure decreases, causing the nitrogen absorbed in body tissues to be released. If this happens too quickly, nitrogen bubbles can form in the bloodstream, leading to decompression sickness (DCS), also known as “the bends.”

Additionally, the expanding air in a diver’s lungs, sinuses, and buoyancy control device (BCD) can cause injuries if not properly managed. A controlled ascent allows for:

• ✔️ Safe nitrogen release from tissues
• ✔️ Prevention of lung overexpansion injuries
• ✔️ Better buoyancy control to avoid rapid, uncontrolled ascents

Why Different Depths Require Different Ascent Rates

The rate of ascent should slow as a diver approaches the surface because:

• The pressure difference per meter (or foot) increases in shallower water.
• Expanding gases can accelerate ascent if not controlled.
• The last 10m (33ft) are the most critical for gas expansion and off-gassing.

Recommended Ascent Rates by Depth

These rates ensure a gradual pressure reduction, allowing nitrogen to off-gas safely and minimizing the risk of an uncontrolled ascent due to expanding gases.

Ascent Rate Considerations for Each Depth Range

➡️ From Below 20m (66ft) to 20m → 10m per minute (33ft per minute)

• In deeper depths, tissue nitrogen saturation is higher, but the pressure difference per meter is lower.
• A slightly faster ascent is acceptable here, but buoyancy control is key—vent small amounts of air from your BCD as you rise.

➡️ From 20m (66ft) to 10m (33ft) → 5m per minute (16ft per minute)

• The pressure difference becomes more significant, and nitrogen release accelerates.
• Slow your ascent to half the previous rate to avoid excessive nitrogen bubble formation.
• Continuously monitor buoyancy changes and adjust your BCD gradually.

➡️ From 10m (33ft) to Surface → 3m per minute (10ft per minute)

• The most critical stage of the ascent due to rapid gas expansion—air in your lungs, sinuses, and BCD can double in volume in just 10m.
• This slow ascent rate reduces the risk of lung barotrauma and rapid buoyancy changes.
• A safety stop at 5m (15ft) for 3 minutes is highly recommended.

How to Control Your Ascent Without a Dive Computer

If you’re diving without a dive computer to measure ascent rates, you can use natural cues and techniques to regulate your speed:

1️⃣ Watch Your Bubbles

• ✔️ A common rule of thumb: Ascend no faster than your smallest bubbles.
• ✔️ Large, fast-moving bubbles indicate you’re going up too quickly—slow down!

2️⃣ Use a Fixed Reference

• ✔️ Ascend along a mooring line, anchor line, or reef wall to maintain a steady pace.
• ✔️ If in open water, practice neutral buoyancy and use slow, controlled fin kicks.

3️⃣ Time Your Ascent

• ✔️ If you know the recommended ascent rate, use a dive watch to track time.
• ✔️ Example:
• 10m per minute: It should take 2 minutes to ascend from 30m (100ft) to 20m (66ft).
• 5m per minute: It should take 2 minutes from 20m to 10m.
• 3m per minute: It should take over 3 minutes from 10m to the surface.

4️⃣ Manage Your Buoyancy Proactively

• ✔️ Vent air from your BCD in small bursts to prevent an uncontrolled rise.
• ✔️ Control your ascent using slow, steady kicks, rather than inflating or deflating your BCD too aggressively.

5️⃣ Perform a Safety Stop

• ✔️ Always pause at 5m (15ft) for 3 minutes before surfacing, even if you feel fine.
• ✔️ This extra time allows residual nitrogen to off-gas safely.

Final Thoughts

A slow and controlled ascent is one of the most essential safety skills in scuba diving. By adjusting your ascent rate based on depth, monitoring natural cues, and using proper buoyancy techniques, you can significantly reduce the risks of decompression sickness and lung injuries.

Whenever possible, use a dive computer to monitor your ascent rate, but always be prepared to ascend safely using alternative methods.

The key to a safe dive is not just the descent—it’s mastering the ascent!

Happy and safe diving!