Decompression Sickness: How I Approach Safer Diving on a Liveaboard

After several days of diving in the Similan Islands, it is easy to get caught up in the excitement.

You have already seen turtles, reef sharks, schools of fish and perhaps a manta ray. Tomorrow there is another early-morning dive, followed by two or three more during the day. Your dive computer is still giving you plenty of no-decompression time.

So why worry?

For me, decompression safety isn’t about being afraid of diving. It is about understanding that every dive is part of a bigger picture, especially when you are doing repetitive dives over several days on a liveaboard.

A typical Similan Islands liveaboard itinerary can involve three or four dives a day across several consecutive days. Some dives are relaxed and shallow. Others may involve deeper sections, currents, or simply more physical effort. Your dive computer is an important tool, but it is only one part of the equation.

After years of diving, I think about decompression safety quite simply: plan sensibly, leave yourself some margin, look after your body and don’t feel that you have to do every dive just because it is on the schedule.

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What Exactly Is Decompression Sickness?

When we descend underwater, increasing pressure causes our bodies to absorb more inert gas, primarily nitrogen when breathing normal air.

As we ascend, the surrounding pressure decreases and our bodies gradually release that nitrogen through the lungs.

Decompression sickness (DCS) can occur when this process results in problematic gas bubbles forming in the body. Symptoms can vary and may include unusual joint or muscle pain, tingling, numbness, weakness, dizziness, unusual fatigue or other neurological symptoms. These symptoms can appear shortly after a dive or later.

The important thing is not to try to diagnose yourself. If you develop unusual symptoms after diving, tell your dive professional and seek appropriate medical assessment.

But DCS is also not something recreational divers should spend their entire holiday worrying about. Good diving practices are about reducing risk, not trying to eliminate every possible risk from an activity conducted under pressure.

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Your Dive Computer Is a Tool, Not a Permission Slip

Modern dive computers have made recreational diving considerably easier to manage. They track depth and time and calculate your decompression status using mathematical models. But I don’t think a computer should be treated as a permission slip.

If your computer says you have five minutes of no-decompression time remaining, that doesn’t mean you need to use all five minutes.

Personally, I prefer to leave a generous margin on most dives. There is rarely a good reason to finish every dive right at the edge of your no-decompression limit, particularly when you are doing several dives a day for several days.

This becomes even more relevant on a Similan Islands liveaboard. Imagine doing four dives today, another four tomorrow and continuing the same pattern for several days. Your body is not starting from zero every morning. Previous dives and surface intervals are part of the bigger picture.

I’d rather finish a dive thinking “we had plenty of time” than “we squeezed every last minute out of the computer.”

I Prefer Dives That Naturally Get Shallower

One of the simplest things I try to do is make the dive profile naturally become shallower as the dive progresses. Go to the planned depth, explore, and then gradually work your way shallower.

This works particularly well around the Similan Islands. The granite formations create different levels, cracks and reef areas, so there is often no need to repeatedly descend and ascend just to find something interesting.

A smooth profile also makes gas management and buddy awareness easier.

Of course, not every dive can be perfectly linear. Currents, marine life and the site itself can change the plan. But when there is a choice, I prefer simple and controlled over unnecessarily complicated.

Don’t Rush the Last Few Metres

The end of a dive is sometimes when divers become distracted. The interesting part is over. The camera is away. The safety stop is finished. Someone signals that it is time to go up.

The ascent from the safety stop to the surface should be the slowest part of the dive. There is a large relative change in ambient pressure as you move from five metres to the surface, and these final metres are often when problems occur. Don’t turn it into a race for the surface.

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Your Body Is Part of Your Dive Plan

We spend a lot of time talking about depth, bottom time and dive computers. But your body is also part of the equation.

Consider a diver who is within their computer limits but has slept badly, become dehydrated, is cold after several dives, has fought a strong current and is exhausted from several consecutive days of diving.

Technically, the dive profile may look acceptable. But the overall situation isn’t ideal. This is why I don’t think decompression safety can be reduced to a single number on a computer screen.

Thailand’s tropical climate makes hydration particularly important. Sitting on a hot dive deck between dives can mean losing more fluid than you realise. Stay reasonably hydrated throughout the day rather than trying to drink huge amounts immediately before a dive.

Sleep matters too. A dive computer knows your depth and time. It doesn’t know whether you slept three hours. On a liveaboard, fatigue can build up surprisingly quickly. If you are exhausted, there is absolutely nothing wrong with sitting out a dive. In fact, I would rather have a diver skip one dive and come back rested than force themselves into the water simply because they paid for it.

The same applies to alcohol. Enjoying a drink after the diving day is finished is one thing, but alcohol and diving don’t belong together. Alcohol can affect judgement, coordination and reaction time, while heavy drinking can also interfere with sleep and hydration.

And then there is current. At sites such as Koh Tachai Pinnacle and Richelieu Rock, conditions can sometimes make a dive more physically demanding. One of the easiest mistakes is trying to prove that you can swim against the current. You don’t have to. Use the reef, topography and your dive team’s plan to your advantage. If the current is stronger than expected, adjust the dive rather than turning it into a swimming competition. Read about our article on the currents in Similan Islands here.

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Nitrox Can Be Useful on a Liveaboard

For repetitive diving, Nitrox can be a useful option. Enriched Air Nitrox contains more oxygen and less nitrogen than standard air. When used correctly, this can reduce nitrogen exposure on the same dive profile.

That can make Nitrox particularly attractive on a multi-day liveaboard trip, where you may complete several dives every day. But Nitrox isn’t simply “safer air.”

The higher oxygen concentration introduces oxygen exposure considerations and a maximum operating depth. You need the appropriate training and must analyse the cylinder and plan the dive correctly.

On board MV DiveRACE Class X, divers can take the RAID Enriched Air Nitrox Course and learn how to analyse and plan Nitrox dives properly. For anyone planning to do more liveaboard diving, I think it is one of the most useful additional diving qualifications to have.

Learn more about the RAID Enriched Air Nitrox Course on DiveRACE here.

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Sometimes the Safest Decision Is to Skip a Dive

This is probably the most important thing I would tell any diver doing a multi-day liveaboard: You don’t have to do every dive.

There can be a strange pressure on a liveaboard because the diving is right there. You wake up, gear up and jump into the water. So when the crew announces the next dive, the natural reaction is:

“Why wouldn’t I go?”

But imagine it is your fourth day of diving. You are tired, slightly cold and your legs feel heavy. The next dive is expected to involve more current than the previous one.

You can go. Or you can have breakfast, drink some water, relax on deck and join the following dive feeling fresh again. I know which option I prefer.

At DiveRACE, we want our guests to enjoy as much diving as possible. But more diving isn’t always better diving. Sometimes the smartest dive is the one you decide not to make.

Don’t Forget the Flight Home

Your decompression planning doesn’t end when you climb back onto the boat after your final dive. After diving, your body continues to eliminate residual inert gas. Flying exposes you to reduced atmospheric pressure, so an appropriate surface interval is important.

Always follow recognised no-fly recommendations and the guidance from your training organisation and dive computer. This is something I think about when planning a liveaboard itinerary.

If someone is trying to squeeze in one last dive before immediately heading to the airport, they may be saving a few hours but creating unnecessary pressure on the schedule.

I’d rather finish the trip properly. Have the final dive. Enjoy the boat ride back. Pack without rushing. Leave an appropriate surface interval before flying. The Similans will still be there next time.

Safer Diving Doesn’t Mean Nervous Diving

I don’t think decompression sickness should make divers afraid of liveaboard diving. Quite the opposite. Understanding decompression risk should make you more relaxed, because you know what sensible diving looks like.

For me, it comes down to a few simple habits:

• Stay comfortably within your computer’s limits.
• Make your dive profile as simple and controlled as possible.
• Ascend slowly and don’t rush the final metres.
• Stay hydrated and get enough sleep.
• Don’t dive when impaired or exhausted.
• Don’t fight strong currents unnecessarily.
• Use Nitrox correctly when it suits your diving.
• And most importantly, don’t feel pressured to do every dive.

These aren’t complicated rules. They are simply good diving habits.

After several days aboard a liveaboard, I would much rather see a diver finish the trip saying “I could have done another dive” than “I pushed myself too hard.”

That is how I approach diving around the Similan Islands and the surrounding sites.

The goal isn’t to see how deep we can go, how long we can stay down or how many dives we can fit into a day. The goal is to enjoy the underwater world, dive within our limits and come back tomorrow ready to do it all again. And on a DiveRACE liveaboard, there is usually another beautiful dive waiting for you.

Plan well. Dive conservatively. Enjoy the journey.

Join us on your next Similan Islands liveaboard adventure with MV DiveRACE Class X. Book your trip here.