Text Box: Air Management
Ever heard of the abbreviation SAC? It stands for Surface Air Consumption. Tec divers use it to calculate how much air (or gas) they need for a specific dive profile.
Why should I bother about SAC?Continue below….
Text Box: Turn Pressure
You should know your turn pressure on every dive, regardless of the depth. It is an essential safety aspect of every dive, deep or shallow.
Continue below….
Text Box: ITC Scuba
for lovers of the underwater world

Theuns van Niekerk

Rebreather, Tec & Mixed Gas

Instructor &

Instructor Trainer

Text Box: Equipment, Skills, Experience (ESE)
Avoiding trouble underwater comes down to three simple elements. If you neglect any of these three you increase your risk of a bad experience.
Equipment
You don't always need the latest and the greatest in equipment to have a safe diving experience. But make sure it is in good working order. Make sure it has been serviced according to the manufacturer’s requirements. 
Remember underwater is a hostile environment. Corrosion and mineral deposits (i.e. Salt) can deteriorate any equipment.
Skills
When you start out with scuba diving your instructor will teach about 20 basic skills to make your diving experience as safe as possible. 
Continue below….
Text Box: Trouble Underwater (continued)
As you progress in becoming a more advanced diver or even taking up more advanced technical diving your skill sets will be expanded. Some old skills will be taken to a new level of proficiency.
Experience
This is the one element you cannot buy. Experience comes with time and  in scuba diving, you get your experience underwater. No matter how much talking you do on land, or how much you visualize your next dive, if you haven't done the time underwater, you won’t have the experience.
Text Box: Air Management (continued)
SAC can make you a safer diver. Talk to any seasoned diver and you will hear horror stories of divers running out of air while on a 30m dive. The survivors of these incidents usually have an air donor to thank. Some gracious soul that had enough air nearby to give them their spare regulator.
These types of incidents are totally unnecessary and can easily be avoided with a little bit of planning, AND knowing your SAC.
For example if you have an SAC of 25, it means you need 25 liters of air per minute at surface pressure.
Pressure underwater
If you descend to 10m, the ambient pressure doubles from 1 Bar at the surface to 2 Bar at 10m. (Remember those pressure calc in your Open Water Course?).
Deeper? You need more air
Getting back to the SAC. If you need 25 liters per minute at the surface, you need 50 liters per minute at 10m (25 lit/min x 2 Bar = 50 lit/min).
If you dive to 20m, the ambient pressure is 3 Bar, and you need 25 lit/min x 3 Bar = 75 lit/min. And so it increases as you go deeper. Every 10m equates to 1 Bar pressure, plus 1 Bar at the surface.
Quiz
If I plan to dive to 20m for 30 minutes, how much air will I need if I have an SAC of 25 lit/min?
What is the ambient pressure at 20 meters? 20m = 2 Bar + 1 Bar at the surface = 3 Bar ambient pressure.
What is my SAC? Lets assume my SAC is 25 lit/min.
Air needed per minute: 3 Bar x 25 lit/min = 75 lit/min.
Air needed for dive: 75 lit/min x 30 minutes = 2,250 liters.
Great now you know how much air you need for the bottom portion of the dive, but do you have that much? To calculate how much air is in a scuba tank, simply take the “wet volume” of the tank and multiply it with the pressure. 
Most scuba tanks are 10 or 12 liter tanks, measuring the volume inside the tank without any pressure, commonly known as the “wet volume”. If the tank is full and pressure is measured as 200 Bar, you have 200 Bar x 12 lit = 2,400 liters.
Text Box: Turn Pressure (continued)
What is that?
Turn pressure is the pressure at which you will turn the dive around and return to the entry point, or when you will start your ascend.
The first part of knowing your Turn Pressure is knowing your SAC. How much air will you use, in short.
Then you calculate how long you will need to get back to your ascend point, how long it will take you to ascend, add your safety stop and calculate  how much air you will need to get back to the surface from the furthest point in the dive.
Go no further
It is the same as going on a drive through the country. You need to know when to turn around and head home, so that you still have enough gasoline to make it.
Text Box: What is my SAC?
Measuring your SAC is very easy and you can do it yourself on your next dive.
What you need: 
Your normal Scuba submersible pressure gauge.
A small slate and pencil.
A timer or dive computer that shows the dive time.
While diving, maintain your depth and write down the air pressure in the tank, the dive time and the depth.
Text Box: Continue to dive normally and do what you would normally do, but maintain your depth within +/- 1m. 
After about 5 minutes, again write down the air pressure in the tank, the dive time and the depth.
You can repeat this exercise a couple of times. The more data you collect the more accurate will be the results.
For the sake of explaining the method, lets assume you wrote down the following:
Start:
Tank Pressure 180 bar, time 10 minutes, depth 10 meters.
End:
Tank Pressure 145 bar, time 18 minutes, depth 10 meters.
Back at the surface you can calculate your SAC as follows:
Make sure you know the “wet volume” of your tank. Let’s assume you used a 12 liter tank.
Calculate the liters you used: 180 Bar - 145 Bar = 35 Bar x 12 liter tank = 420 liters.
Calculate the time of the exercise: 18 Text Box: We calculated we need 2,250 liters of air and a full 12 lit tank has 2,400 liters of air. 
But is that enough? Can I do the dive safely?
What about the safety margin of 50 Bar, and the air needed for ascend and the safety stop? You should never have less than 50 Bar in your tank.
So useable air in the tank is actually 200 Bar less 50 Bar = 150 Bar. Thus I only have 150 x 12 lit = 1,800 liters of air available. 
With the 1,800 liters of air I need to do my descend, bottom portion, ascend and safety stop.
So before I even set foot in the water I already know that I cannot do a 20m dive for 30 minutes on a single tank of 12 liter air.
Knowing this limitation has already reduced my risk of an accident!
watch that pressure gaugeText Box: Example
Let me illustrate with an example:
Let’s assume I have an SAC of 25 lit/min. That means I use 25 liters of air per minute at the surface where the ambient pressure is about 1 Bar.
We are doing a dive on a reef and will swim back to our entry point at a depth of 10m, and the swim back will take no longer than 10 minutes.
We also plan for a safety stop at 5m for 5 minutes.
How much air do we need?
The swim back: 10 minutes x (10m is 2 Bar ambient pressure) x 25 lit/min SAC = 10 x 2 x 25 =  500 liters.
The safety stop: 5 minutes x (5m is 1.5 Bar ambient pressure) x 25 lit/min SAC = 5 x Text Box: 1.5 x 25 = 187 Liters
Thus for our safe return we need 500 + 187 = 687 liters, say 700 liters.
Convert that to pressure in the tank. We ask the dive shop what size tanks we have, and they say it is a 12 liter tank. 
Thus the turn pressure is 700 liters / 12 = 58 Bar PLUS 50 Bar for minimum pressure in the tank. Thus our Turn Pressure is 58 + 50 = 108, say 110 Bar.
Now we know our turn pressure, we can agree in our group that we will turn as soon as the first person reaches 110 Bar.
Having this knowledge has already reduced your risk of an unfortunate incident!

3) minutes—10 minutes = 8 minutes.

4) Calculate the ambient pressure of the depth: 10 meters x 1 Bar + 1 Bar at surface = 2 Bar ambient pressure.

5) Your SAC: 420 liters / 8 minutes / 2 Bar = 26 liter per minute SAC.

This is a simple calculation you can make under varying conditions, such as resting, swimming against a current, drift diving, etc.

The result is a SAC you can use to make your next dive even safer.

remember E-S-EText Box: Trouble Underwater
Having trouble underwater can turn an idyllic vacation into a nightmare of epic proportions. 
Even though the underwater world is fascinating and enchanting, it is always good to remember, it is also a hostile environment. There is no air to breathe and whatever you need, you have to take it with you.
Exotic Experience
Scuba diving is one of the most exotic sports you can think of. Every time you submerge you become an explorer. A type of Livingston, on an expedition. You will see new life forms, or corals that look like rocks or plants, but are actually animals. 
Underwater you enter into a world that is foreign to our normal experience. It is liquid and comfortable to touch. Suddenly you can fly in three dimensions like a bird in the sky.
It is no doubt an exotic experience.
Text Box: Keep it Low Risk
To minimize the risk of trouble underwater, talk with your instructor often. Find out about new developments. Like all aspects of our lives these days, Scuba diving is also developing and new discoveries are being made almost on a daily basis. New methods of doing tasks that simplify and streamline old and tedious tasks. 
Make sure your equipment is in top shape, don't risk it with equipment that is faulty or suspect. You can always dive again.
Get underwater as much as you can. Don’t expect to be proficient if you haven't been underwater for a long time. If so then do a refresher course, or take at least go out with an instructor.
Text Box: DIVE COURSES
Rebreather and Tec Diving Courses

ARTICLES & VIDEOS

· Talking Fish

· Trouble Underwater

· Decompression Theory in a Nutshell

· Intimate with a Sea Squirt

· The Reef Experience

· Liluan Wreck

 

EXPEDITIONS

· Gold Treasure on Kuda Maru

· The Coelacanth in Tanzania

· WWII Wrecks in Coron

· Malaysia

· Spiegel Grove - Florida

· Tubbataha - Philippines

· The Akitsushima WWII Wreck - Philippines

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