Surface Interval: Importance and How to Maximize It

Surface Interval: Importance and How to Maximize It

After an awesome dive in the warm and clear waters of Koh Tao, you resurface and wonder when you can dive back into the depths. Your divemaster checks his dive computer and advises you to climb aboard the boat, sit, unwind, and enjoy a surface interval of at least 60 minutes. But why the wait? Why can't we dive incessantly? Why does the human body require breaks from the underwater world we love dearly? And how should we make use of this surface time between dives?


Scuba diving, Sail Rock. Koh Tao

Breathing Under Pressure: Why Does It Change?

Before diving into the details, let's revisit the basic physics of diving. The water's pressure affects how quickly a diver's body absorbs nitrogen while submerged. Remember the concept of atmospheres from your Open Water Course? During scuba training, you learned that the surface pressure is equivalent to 1 atmosphere. As a diver descends into the water, the pressure increases. For instance, the pressure doubles at a depth of 10 meters in salt water, reaching 2 atmospheres. With every additional 10 meters of depth, the pressure increases by another atmosphere.

The air we breathe is mainly nitrogen (79 percent) and oxygen (21 percent). When you inhale, your body uses oxygen, and some of it turns into carbon dioxide, but the nitrogen stays put. Under normal pressure, some nitrogen and oxygen dissolve in your blood and tissues. But here's the twist: pressure on your body rises as you go deeper underwater. When pressure on a fluid (since your body is about 60% water) goes up, it can hold more gas. So, while you're diving, more gas gradually dissolves into your body. Most of the oxygen is used by your tissues, but the nitrogen stays dissolved.

The only way to decrease the nitrogen in your blood is to stay out of the water between dives. Ascending slowly and doing a safety stop also helps. This time, known as the 'surface interval,' allows the nitrogen absorbed during the first dive to gradually leave your body, a process known as 'off-gassing.'


How do you determine when it's safe to dive again?

Diving Table

 After resurfacing from a dive, your body returns to its natural pressure, allowing tissues to release stored nitrogen. By analyzing your dive profile and time spent at depth, you can calculate the pressure group and the necessary surface interval for your blood nitrogen levels to decrease to a safe level. This information is essential for planning your next dive.

The Dive Table provides the minimum surface interval needed between dives. A one-hour surface interval is typical for most dives. By this time, a significant amount of nitrogen has been released, minimizing its impact on the next dive.

However, if your first dive was deep and close to the no-decompression limit, and your second dive is also deep, it's advisable to wait two hours before your next dive. This extra surface time allows for a longer bottom time. If you're using a dive computer, switching it to plan mode will provide real-time information for your safety.

Check out our blog: "Can I Fly After Scuba Diving?"


Now that you understand the Surface Interval's significance, let's consider how to maximize this time.


surface interval in Koh Tao


Aside from allowing your body to off-gas nitrogen, the surface interval can be utilized for other great purposes:

1/ Stay hydrated

Staying hydrated during your surface interval is important to avoid dehydration. While diving, dehydration can occur because the air in the tank is dry, and you don't sweat much underwater. But you might start sweating more once you're back on the surface, especially in Koh Tao's tropical climate. That's why it's a good idea to start drinking water or tea, which we always have on our dive boats. Drink at least a liter of water slowly during your surface interval!

 2/Revitalize Your Body

Boosting your energy levels after an exciting dive is important, and snacks can help. To maintain hydration, we avoid serving salty snacks and offer fruits, toast, jam, and cookies on board. Additionally, we recommend bringing your own diving snacks to ensure you stay energized throughout your dive experience.

 3/Socialize and Connect

Surface intervals offer the perfect opportunity to forge new friendships and bond with fellow divers. You'll engage in fishtastic conversations with your dive buddy for the day and other divers on board.

Explore Marine Life: Use the marine life book onboard to identify and learn more about the fish and creatures you encountered during your dive. Discussing these sightings with fellow divers adds to the excitement and appreciation of the underwater world.

Environmental Awareness: Use the surface interval to reflect on the importance of marine conservation and discuss ways to protect and preserve the ocean's ecosystem with your dive companions.

Marine Photography: If you're into underwater photography, use the surface interval to review and discuss the photos you captured during the dive. Share your favorite shots with your dive buddies and exchange tips and techniques for capturing the perfect underwater moment.

Plan Future Adventures: Use this time to plan future dive trips, explore new dive sites, or discuss potential underwater excursions with your dive buddies. It's a great opportunity to share ideas and expand your diving horizons.


Diving can tire you out: So give your body time to recover! Remember, taking a break doesn't mean being lazy. Lying in the sun after a dive, listening to the ocean's soothing sounds, and watching the clouds drift by is the perfect way to recharge before your next underwater adventure.

 5/Take in the Views

Take a moment to appreciate the breathtaking scenery of beautiful Koh Tao. Whether it's the picturesque coastline, the stunning beauty of Koh Nangyuan, or the vast expanse of the ocean, soaking in the natural beauty above water is as fulfilling as exploring below.


Diving with Enriched Air, or Nitrox, lets you take shorter breaks between dives. Since you absorb less nitrogen, you need less time on the surface to release it, allowing for more dives over several days. This is great if you want to maximize your dive time.

Nitrox also means you can stay underwater longer. With more oxygen and less nitrogen, you can enjoy longer dives. This is especially useful for trips with multiple dives over several days, giving you more time to explore.

Nitrox also reduces the risk of decompression sickness. Less nitrogen absorption means lower chances of getting decompression sickness.

To dive with Nitrox, you need to complete the PADI Enriched Air Nitrox specialty course. The course covers Nitrox diving theory, managing oxygen exposure, and dive equipment considerations. You can do the theory online and choose whether to do just the practical parts or add dives with Enriched Air as well.


Beautiful Koh Tao, Thailand


We hope you see why it's important for your body to lower its nitrogen levels gradually. Safety is our top priority here at Coral Grand Divers, so we take the surface interval seriously and hope you do, too. Next time you take a break between dives, consider how to make the most of it while staying safe. Like any enjoyable activity, having a good time during the surface interval means doing it responsibly.

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