Lesson 132

Lesson three: Flying After Diving and Altitude Diving

Course Complete

Learning Objectives

By the end of this session, I should be able to answer these questions:

1. Why is going to altitude after diving a potential issue?

2. How do flying after diving and altitude diving differ?

3. What are the current recommendations for flying after diving?

4. How do I keep up with the recommendations for flying after diving?

5. Above what altitude do I need to use altitude diving procedures?

Flying After Diving and Altitude Diving

In Section Four, you learned that you need to keep the excess dissolved nitrogen in your body tissues within accepted limits. Failure to do so may allow the nitrogen to come out of solution and cause decompression sickness. The decompression models used in most dive computers and tables are based on surfacing from your dives and making your surface intervals at sea level

Going to a higher altitude lowers the pressure around you at the surface. This means that dissolved nitrogen would come out of solution faster than at sea level. Going to altitude after diving is therefore a possible problem, because the lower pressure can increase the risk of DCS. If you will be flying after diving (or going to altitude by driving over a mountain pass, etc.), or diving at altitude (in a mountain lake), you follow special recommendations and procedures to account for the reduced pressure.

Flying after diving and altitude diving both involve altitude, but they differ and have different recommendations and procedures. When flying after diving (or ascending to altitude after diving), you start and end your dive at sea level (normal surface pressure), and then go to altitude (lower surface pressure). When altitude diving, you start and end your dive at altitude (lower surface pressure).

Flying After Diving Recommendations

Over the years, recommendations for flying after diving have changed. At this writing, the dive medical community’s recommendations for flying after diving are:

For no stop dives:

Single dives (no repetitive dive) – A minimum preflight surface interval of 12 hours is suggested.
Repetitive dives or multiday dives (diving every day for several days in a row) – A minimum preflight surface interval of 18 hours is suggested.

Dives requiring emergency decompression stops:

A minimum preflight surface interval greater than 18 hours is suggested.

These recommendations are based on a cabin altitude pressure range of 600-2400 metres/2000-8000 feet. While these guidelines represent the best estimate presently known for a conservative, safe surface interval before flying for the vast majority of divers, remember that no flying after diving recommendation can guarantee that decompression sickness will never occur. There always may be divers whose physiological makeups or special dive circumstances result in decompression sickness, even when following the recommendations.

As with other aspects of diving, you’re responsible for your own dive safety and behavior. Flying after diving recommendations change as we learn more about how pressure changes affect the body, so follow the most current recommendations, which can be found in diver publications and websites including diversalertnetwork.org.

There are presently no recommendations for driving to altitude after diving, so the prudent practice is to be conservative. The longer the interval between diving and going to altitude, the lower the risk. In areas where driving to altitude is common, local divers may have a procedure they use. Some divers use the flying after diving recommendations for driving to altitude. While these practices appear to work for many divers, few (if any) have had formal testing. So, use them conservatively. If in doubt, take a longer surface interval before driving to altitude.

Altitude Diving

With most dive computers and dive tables (including the RDP Table and eRDPML), you need to use altitude diving procedures if diving at an altitude of 300 metres/1000 feet or higher. Altitude diving procedures with dive computers may differ. Some automatically adjust, some have settings you use and others can’t be used at altitude (see the manufacturer literature).

To use most tables (including the RDP Table and the eRDPML) at altitude, you use a special table that converts your actual depth to a theoretical depth that adjusts for the pressure difference. If you’re interested in altitude diving or will be diving at altitude locally, you can learn the procedures in the Altitude Adventure Dive in the Advanced Open Water Diver course, or PADI Altitude Diver course.

knowledge review and quiz

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