Understanding Decompression Sickness: 3 Key Factors Every Diver Should Consider

Understanding Decompression Sickness: Highlights three critical factors every diver must monitor—time at depth, ascent rate, and nitrogen absorption—to stay safe beneath the surface.

Over the past week, I've learned about three separate incidents involving divers—one led to a fatality, and the other two involved decompression sickness (DCS). While I don't have all the details, surrounding each case, it was a sobering reminder that DCS remains a real and present risk in our sport—even for certified and experienced divers. That’s why I felt compelled to take a moment and talk about the key factors that contribute to DCS and what we, as divers, can do to better understand and manage that risk.

DCS doesn’t just happen when divers push past limits—it can occur even when we stay within our computers' recommendations. That’s because decompression sickness results from a complex interplay of factors, including your dive profile, thermal and exertion stress, and your individual physiology. Here’s a closer look at each:

1. Dive Profile: More Than Just Depth and Time

Your dive computer calculates nitrogen loading based on the profile you follow—but not all dive profiles are equal, and subtle differences can make a big impact.

Critical elements include:

• Time at each depth – Longer periods at deeper depths lead to more nitrogen absorption.

• Ascent rate – Ascending too fast reduces the body’s ability to safely off-gas.

• Stop depths and durations – Safety stops or required decompression stops must be respected; skipping or shortening them increases DCS risk.

• Breathing gases used – Enriched air (Nitrox) can reduce nitrogen exposure but requires proper use within depth limits.

Multi-level dives, reverse profiles, or short surface intervals between dives can all create conditions where nitrogen builds up faster or isn’t eliminated efficiently—even if you stay within your no-decompression limit (NDL).

2. Thermal and Exercise Stress

The water around you and how hard you’re working while diving also have a big impact on your body’s ability to handle inert gases.

• Cold exposure reduces blood flow to extremities, slowing nitrogen elimination. If you’re cold during ascent or at your safety stop, you may be increasing your risk.

• Physical exertion increases blood flow and nitrogen uptake. Struggling against current, over-kicking, or lifting gear can add stress that the dive computer doesn’t account for.

The takeaway: Stay warm, dive relaxed, and let good trim and buoyancy control reduce unnecessary effort.

3. Individual Susceptibility

Perhaps the most frustrating part of DCS is that what’s “safe” for one diver may not be for another. Everyone's body responds differently to inert gas loading and off-gassing.

Factors that affect personal risk include:

• Age and body fat percentage – More fat tissue can hold more nitrogen.

• Hydration and fitness – Dehydration and low cardiovascular fitness can impair circulation and gas elimination.

• Previous DCS history – If you've had it before, you're more likely to get it again.

Other variables—like alcohol consumption, smoking, illness, or even genetics—can subtly shift your risk on any given day. That’s why listening to your body and making conservative choices is always a smart move.

Final Thoughts

Incidents like the ones I heard about this past week are difficult and sometimes hard to explain—but they also serve as reminders. Decompression sickness isn’t just about breaking the rules; sometimes it happens when the rules don’t account for every variable.

As divers, our best protection is knowledge and awareness. Understand the full picture of your dive profile. Stay warm and relaxed in the water. Know your body and dive within your true limits—not just what your computer allows.

Stay safe, dive smart, and let’s continue learning and looking out for each other.~ Dive Buddy Scuba