When you think of altitude diving, you probably picture yourself enjoying the beauty of a crystal clear alpine lake in Europe or the Western United States. The fact is, any dive you take at an altitude of more than 1,000 feet is considered an altitude dive by PADI’s definition. Before you plan to dive at altitude, it’s vital that you have a thorough understanding of altitude dive tables. This quick primer will help get you started.
Keep it Simple with TOD
One of the best references available for attitude diving is the PADI Adventures in Diving manual, which contains tables that you can use to convert the dives you make at altitude to equivalent dives at sea level, in the ocean. Known as Theoretical Ocean Depth (TOD), this method makes it easy for you to use a standard table such as the RDP (Recreational Dive Planner) to plan altitude dives quickly and easily.
One cautionary note to keep in mind when using TOD is that although basic altitude conversion tables are in fact correct in principle, they are based on the assumption that you’ll be diving in salt water or sea water rather than in fresh water, which is where almost all altitude diving takes place.
Luckily, it is very easy to correct diving tables for fresh water. You probably remember that one atmosphere of pressure is exerted for every 33 feet of sea water (fsw) and for every 34 feet of fresh water (ffw). This makes it simple and straightforward to transform altitude diving tables meant for fsw into ffw values. To do this, multiply the Theoretical Depth at Various Altitudes value by 33/34. Next, multiply the Safety/ Emergency Decompression Stop Depth value by 34/33.
Understand Your Depth Gauge
Besides ensuring that you’re planning your dives using the correct numbers, it’s important that you understand how your depth gauge will function when you’re diving in fresh water while at altitude. Some electronic depth gauges are calibrated to automatically read depth only in sea water and must be recalibrated before fresh water diving, however most contemporary dive computers can be easily reset so that they read depth in fresh water. Some models even convert themselves automatically when they are used above a certain altitude, such as 2,000 feet above sea level. Spend some time familiarizing yourself with your equipment and take the opportunity to learn how it will function when you dive at altitude. If you’re uncertain about your depth gauge or dive computer, seek assistance from the manufacturer or a retailer who is familiar with the way the model you have operates.
If you are unfamiliar with diving at altitude and have the opportunity to work with a local dive shop that operates in the area where you will be conducting your first altitude dives, don’t be shy about discussing dive tables, equipment, safety stops, and other factors. The first few calculations you make might be a bit tricky, but with even a small amount of practice, you’ll find that they come easier and altitude diving becomes almost second nature.