What is Altitude Diving and what do you learn in the PADI Altitude Diver specialty course?

 

Simply put, any dive above sea level is considered an altitude dive.   From a scientific/commercial diving point of view, that could be 300 ft above sea level for dives deeper than 145fsw [NOAA Diving Manual].   For the purposes of recreational altitude diving, any dive at an altitude above 1000 feet or 300 meters is considered an altitude dive and requires some special planning.  Learning and practicing these procedures are the heart of the PADI Altitude Diver course.

Diver signalling ok before descending at Causey Reservoir

Diver at Causey Reservoir near Huntsville, UT. Altitude 5700ft

Before we get into the details, you might be asking why we need to plan our dives differently at altitude.   Most dive planners, either tables like the PADI/DSAT Recreational Dive Planner or a dive computer  account for your surface interval and related nitrogen release as if you were at sea level.   At altitude that’s not the case.    For a given amount of nitrogen in your body, you’ll be releasing faster at altitude than you would at sea level due to the difference in atmospheric pressure.

You can take one of two approaches to this: either come up with new dive tables for each altitude or come up with a way to correct or adjust the existing tables.   The most common approach is the later: an adjustment to the existing tables.    The most common adjustment is to plan the dive as if it was deeper than actual and that you had absorbed more nitrogen on the dive.   So rather than planning for a faster off-gassing of nitrogen, you plan on having more nitrogen in your tissues.    There are several published tables available.   For example, there is a copy in the PADI Adventures in Diving manual, a version in the NOAA Diving Manual and there are slates available.    For most divers, I recommend having a slate that you can take with you on your dive.

The table that shows up in PADI Adventures in Diving has depths in 10 foot increments.   You take your actual depth, round to the next deepest 10-ft mark and then follow along to your altitude, again rounding–in this case to the nearest 1000ft.

For example, a dive to 57 feet at 5,700ft altitude:

  • First, round the depth of 57 feet to 60 feet
  • Second, round the altitude of 5,700 feet to 6,000 feet
  • Look at the table for the altitude adjusted depth.  In this case, 75feet.   Plan your dive for that depth.

 

During the PADI Altitude Diver course you’ll practice dive planning for two dives.   Also, as you can see, we have to do a good amount of rounding.   For that reason, you’ll also compare depth gauges with your buddy or your instructor.   When you’re making altitude dives with your buddy, always go with the most conservative depth, in this case deepest.

For example:

  • Your depth gauge reads 58 feet.   Your buddy’s reads 61 feet.
  • Using the same dive site as above, at an altitude of 5,700 ft, your adjusted depth would be 75 feet.   Your buddy’s would initially round to 70 feet and then altitude adjust to 87 feet.
  • Even if you use a dive planner like the PADI eRDPML that plans dives in 5-foot increments, this becomes a 15-foot difference in dive planning.   To avoid potential decompression illness(DCI) issues, plan for the deeper depth.

If you look at the NOAA Diving manual, there is a table with depths in 5-foot increments.   For scientific and commercial divers that have a diving support team, this added flexibility can be handy.   For recreational divers, I wouldn’t suggest it as you start pushing the envelope and can be at higher risk for DCI.

 

During your Altitude Diver Specialty course, you’ll also look at:

  • Arriving at altitude.   Driving up a canyon to a dive site is like ascending during a dive.   At lower altitude, you were under higher pressure and have absorbed nitrogen.   As you ascend (drive up the canyon), you are going to a reduced pressure.   Making an actual dive at that point is now like making a repetitive dive.
  • Altitude diving is often done in mountain lakes that are cold.  Hypothermia is a concern and will be addressed during the course.
  • Your dive equipment can change.   For example, your wetsuit is neoprene rubber with bubbles blown in it.   At altitude, they are larger due to reduced pressure.   So the insulation qualities are different from diving at sea level and your buoyancy profile might also be different.
  • Hypoxia: if you’re not used to the altitude, you might find you are easily out of breath.   That’s because your body isn’t used to the reduced pressure and related lack of oxygen.
  • Safety stops:  Safety stop depths are also adjusted, in this case they are shallower.

 

Are you ready to make those altitude dives?   Contact Jon to get started with your PADI Altitude Diver Specialty Course.

While the Altitude Adventure dive covers much of the Altitude Diving information, if you dive often at altitude, you should complete the Altitude Diver specialty course.   [Every dive in Utah is an Altitude dive!]

Extra details: Where do the altitude corrections come from?

Altitude corrected depths are calculated by dividing the actual depth by the nominal atmospheric pressure at the altitude you’re diving at.   For example, at an altitude of 5,000 feet, the nominal atmospheric pressure is 0.83 ATM.   A dive to 60 feet would be calculated by dividing 60 by 0.83, resulting in an adjusted depth of  72 feet.

Safety stops are calculated in a similar way.  In this case they are calculated by multiplying the depth by the nominal atmospheric pressure.   So, 15 feet X 0.83 = 11.62 feet.   That’s then rounded to 12 feet.

To learn more, check out the NOAA Diving Manual section on Altitude diving.