Dive Computer

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Altitude Diving Tips And Refresher

I did a lecture on Altitude Diving last night and it made me thing about putting a "Tip Sheet" together. Following is a list of tips to remember when Altitude Diving.

1. Any dive between 1000 feet and 10,000 feet is an Altitude Dive

2. There is relatively little test data for altitude diving, flying after diving or driving to altitude after diving.

3. At sea level, the diver is surrounded by one atmosphere of pressure. At 10,000 feet, the pressure is .714 atmospheres (a 30% decrease in pressure). This is the same pressure change as 10 feet of seawater, which we know makes a big difference in our no-decompression limits. As we'll see, this must be accounted for when using the RDP or any other dive table or dive computer.

4. Besides decompression sickness, there are heightened concerns for Hypoxia and Hypothermia when divng at Altitude.

5. Unless the actual depth is converted to a theoretical depth for table use and special procedures are followed, at altitude the pressure ratio can exceed the maximum limit intended by the table or dive computer, increasing the possibility of decompression sickness.

6. There are several equipment considerations when diving at altitude: (1) Air, trapped inside the cells of a wetsuit, expands at altitude, possibly making you more buoyant. Do a buoyancy check. (2) Different Gauges act differently at altitude, check with your gauge manufacturer and know what kind of gauge you have and how altitude effects it. (3) Computers either automatically adjust for altitude, need to be manually adjusted for altitude or have no adjustment for altitude. Know your computer!

7. When using an RDP or Table to plan your dive, consult the Theoretical Depth Conversion chart first and plan your dive using your theoretical depth, not your actual depth. Adjust your safety stop accordingly.

8. Ascend from depth on an altitude dive at a rate not to exceed 30 feet per minute. Safety stops are mandatory on all dives.

9. Make no more than two dives per day when diving altitude.

10. When arriving at altitude, wait 6 hours for your body to acclimitize or adjust your dive profiles to account for the residual nitrogen in your system as a result of the increase in altitude. When diving above 8000 feet, always wait 6 hours.

11. When using charts and tables, always round conservatively - whether it be up or down.

12. Consult your certification agency or Divers Alert Network for recommendations on altitude or flying after diving. It is generally recommended not to increase your altitude more than 2000 feet for a period of 24 hours after diving.

13. Do not make repetitive dives at different altitudes. Always wait a minimum of 6 hours when diving between altitudes.

14. If you are diving at altitude, seek proper training and get certified. Tip sheets and articles found on the Internet are no substitute for training. Dive within your training limits.

Dive safe!

About the Author

PADI Master Instructor, NAUI Instructor Trainer, SDI Instructor Trainer, Technical Dive Instructor, DAN Instructor, SeaSigns Instructor Examniner

Interested in becoming a great diver?
Please visit http://www.academyofscuba.com

How To Choose a Dive Computer - By Leisurepro


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Dive Computers

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Dive Computer Algorithms

What are Dive Computer Algorithms?
The dive computer is used to calculate your maximum dive time which allows for a longer and safer dive. The dive computer as took over from the dive table as the diving tool to calculate all your necessary parameters to enjoy scuba diving.

Dive computers use algorithms to calculate these safe diving limits. They will make adjustments for both fast tissue groups and slow tissue groups. It uses this information to estimate the nitrogen in your body. Based on the amount of time you've been submerged and your depth, from this the computer then calculates how much longer you can safely remain underwater.

Different Type of Algorithms
Algorithms vary by model from each manufacturer and only a few algorithms are actually used. Some algorithm used may also be a modification of an existing algorithm. When you want to consider buying your next dive computer, the main feature to look at is the algorithm that the air decompression limit monitor uses.

Algorithms with different manufactures use some varying factors in their algorithms such as mentioned with fast and slow tissue groups. The solubility, permeability, and blood contact for a given tissue, say for example a kidney, is called a "tissue compartment or tissue group." Dive computers use these "tissue compartments" to simulate the effect of a gas on your body at depth. The more "tissue compartments" a computer measures, the more accurate (theoretically) the computer can gauge the effect of a dive on your body. 9 to 12 compartments is fairly standard, but a few consumer models have 16 or more.

Here are four of the main algorithms used for dive computers:

Group 1: Haldane/Spencer Algorithm
The Haldane/Spencer model uses test results from PADI's Diving Science and Technology and was developed by Rogers and Powell. Within their algorithm they use 12 separate tissue compartments. Oceanic and Sherwood use this algorithm model for their dive computers.

Group 2: Modified Haldanian Algorithm
This algorithm model was used by Mares and is based on nine tissue compartments. Now the latest Mares dive computers use the Reduced Gradient Bubble Model.

Group 3: Suunto Reduced Gradient Bubble Algorithm
This model is based in part on work by Wienke and Hamilton and uses nine tissue compartments. Suunto were the first to use the RGDM and now other manufactures are starting to use it too. The big difference of this algorithm is they consider micro bubbles that are in the blood stream as a result of nitrogen build up. The theory was they consider that these micro bubbles are a precondition of larger bubbles which can lead to DCS.

Group 4: Uwatec Buehlmann ZH-L8 ADT Algorithm and the ZH-L8 ADT MB.
This algorithm model uses eight tissue compartments and has been recently updated with two additional letters, the Buhlmann adaptive model has been expanded to be called the ZH-L8 ADT MB which stands for micro bubble. This algorithm is used by Uwatec and Scubapro.

Short fall of Algorithms
Algorithms may not be able to account for age, previous injury, ambient temperature, body type, alcohol consumption/dehydration, and patent foramen ovale(hole in the heart).

Which Algorithm is the best?
Removing of factors like cost, looks, other features etc then the more "tissue compartments" a computer measures, the more accurate (theoretically) the computer can gauge the effect of a dive on your body. 9 to 12 compartments are fairly standard nowadays, but a few dive computers are now using 16 compartments.

Even if two algorithms have the same results, manufactures will add there own factor of safety so they can set there dive computers to aggressive or conservative. An aggressive computer gives more bottom time than a conservative dive computer, and it's wise to understand the properties of one's own dive computer to ensure it fits the skill and comfort level expected.

About the Author

Simon James has been diving for 15 years and is an authority in the field so take a look at this website called M2 Nocturnal Lights and SLX 300 Nocturnal led dive lights

Dive Watch Computer Review. The Top 5.


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