As divers, we all know the importance of the surface interval. When we return to the surface from a dive, even one within the No-Decompression Limits (NDL), there is still some residue nitrogen in our body tissues. Different types of tissue absorb and release nitrogen at different rates that are called a half-life.
While, at the surface, the body will continue to release the nitrogen, hence the term “off-gas”. The longer the surface interval, the time between two dives, the more nitrogen is off-gassed. Fewer nitrogen means, the more we can take in on our next dive before reaching the NDL.
Once we reach the surface, we are in our bodies natural state and the tissue will give up it stored nitrogen at its half life rate.
Using our dive profile and our time at depth, we can start calculating the pressure group and residual nitrogen time. We will use this information to profile or plan our second dive.
The process will tell us our minimum surface interval required to do the dive we want or show where a modification needs to be made to the next dive plan.
On most dives, a one hour surface interval is standard. At this point a substantial percentage of nitrogen has been released and the impact on a second dive is not too great.
If the first dive was deep and very near the NDL with a second dive also deep, Then it is not uncommon to wait two hours before your next dive.
The extra dive will give you a longer bottom time. Of course, if you are using a dive computer, placing it in plan mode will show you the information in real time.
Also read: Diving with Nitrox vs. Air The Pros & Cons
What You Should Do on a Surface Interval
In addition to the off-gassing requirements, the surface interval serves other purposes. If you are diving at two separate dive sites, the dive boat will relocate during this time. Also, you will swap your old empty tank for a filled one.
While on many dive boats a boat crew will do that, it is important that the diver verifies the equipment is set up properly.
Here are five things you can incorporate into your surface interval next time you are out exploring the undersea world.
Rehydrate yourself properly in between dives
A mild dehydration is very common on dive boats. The breathing gas we are using underwater has been dehumidified when the cylinder was filled. While underwater we do not sweat very much, as soon as we reach the surface that can change.
If diving in hot weather, the exertion of getting back on board the dive boat can have us sweating under our wetsuit. Even in cold weather a dry suit can make us sweat.
Start with water and if you wish a glass of juice or a sports drink. The sports drink should not have caffeine. Plan on slowly consuming at least a liter of water during your surface interval, more if you are sweating while on board.Planning a scuba trip? Then you should download the ultimate scuba dive checklist just like 5000+ other divers already so you will not forget to bring anything.## Enjoy the Scenery
Do you know that cruise ship passengers at tropical ports will pay up to $100 for an hour boat ride and another hour of snorkeling?
Unless the dive boat is going to move soon, consider passing up your dive gear and then snorkel for a while if you are over a reef with good visibility. Snorkeling at the surface is very relaxing, and a good means to relax.
It is very likely you will spot marine life like Dolphins and turtles who often seem to want to check out dive boats.
You can always strike up a conversation with others if they seem to be in the mood.
Plan Your Next Dive
Set aside a few minutes of the surface interval, to review the finished dive with your dive buddy. It does not need to be a blow by blow replay of the dive. Just review what you think is needed. Check air consumption and if you followed the dive plan. Follow this with a review and if necessary a modification of the next dive plan.
Eat a Light Meal or Snack
A light meal or a snack is an excellent way to restore energy levels. Do not consume salty foods like potato chips, as this will make your mouth dry and increase your thirst. Fruits and nuts are good choices for a snack. You do not want anything heavy that will cause your digestive track to work hard. Also, avoid items that can cause heart burn. The five-alarm chill can wait until after the dive.
Rest and Relax
Leave yourself some quiet time to rest both mentally and physically. Take a nap if you like. I know a diver, that once her gear was all stowed, she would drink some water and curl up like a kitten and go to sleep.
She went to sleep so fast one time, the dive master came rushing over with an emergency oxygen bottle. He thought she passed out. It was funny afterward, but the dive masters reaction was excellent.
Decompression illness due to excess nitrogen or an embolism can occur very rapidly and often within the first ten minutes of surfacing.
What are your favorite things to do in between dives?
Let us know in the comments below
Planning a scuba trip? Then you should download the ultimate scuba dive checklist just like 5000+ other divers already so you will not forget to bring anything.
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