Cautionary tales about going to altitude after diving describe one of the core rules taught in any open-water course. But divers often have questions about specific recommendations because the rules occasionally change. Here at DAN, we've made the relationship between altitude and diving one of our primary studies for many years, and if we do say so ourselves, we're experts on the subject, regularly helping to analyze and update the flying-after-diving rules taught by training agencies worldwide. Here are answers--using the most scientifically up-to-date information our researchers can provide--to the three most common altitude and diving questions we're asked on our emergency hotline and medical information lines.
Can I dive immediately after flying?
Sometimes. But if you don't, it won't be for nitrogen-related reasons. There are no set guidelines for when to make your first dive. The issue here is fitness. Air travel can leave divers mildly dehydrated, fatigued, improperly nourished and generally stressed. Long-distance travel compounds the problem; the more time zones you cross, the more these factors affect your general condition. And the more you are affected, the more you need to factor this into your early dive planning.
Do this by building some pre-dive flight recovery time into your travel plans, allowing you to rehydrate, rest and eat. Dehydration is thought to contribute to DCS risk, so it's critically important not to start diving with a hydration deficit. Fatigue can also be a performance and safety issue--if you're tired or lacking energy, you might not respond normally to strenuous or emergency circumstances--so make sure you're well rested.
Of course, if you're traveling on a shorter flight and you arrive at your destination rested, hydrated and properly nourished, then diving may be possible. You need to assess your condition honestly and objectively. It isn't worth compromising your safety--or ruining your whole trip--because you're in a hurry to make the first dive.
How long do I have to wait before flying after diving?
The concerns of heading to altitude too soon after diving are the same as those when you ascend from your dive too quickly because the same scientific principles apply: Going to altitude takes you to an area of lower outside pressure, meaning residual nitrogen still dissolved in your blood can come out of solution as bubbles if the ascent isn't slow enough to let your body off-gas. This is why it's so important to ensure you've off-gassed any nitrogen in your system before going to altitude. The more diving you do, the more residual nitrogen you'll amass, so the amount of time you should wait relates directly to the type of diving and how many dives you make in a given period of time.
We recommend waiting at least 24 hours before flying after diving--better safe than sorry--but if that's not possible, the following shows the minimum guidelines for different diving circumstances, based on flying in commercial aircraft.
- A single dive within recreational limits: 12 hours
- Multiple days/multiple recreational dives: 18 hours
- Decompression diving (planned or unplanned): 24 to 48 hours
These guidelines are not infallible, and they apply only to divers who haven't experienced any DCS symptoms. If you've experienced DCS symptoms during your dive trip, don't fly at all. Instead, call DAN's emergency hotline (919-684-4DAN) immediately, and get checked out by a doctor familiar with diving.
Just as we are taught not to "push the tables" in reference to our bottom times, don't "push the recommendations" when it comes to your diving and flying interval. Leaving time between your last dive and your flight home is part of dive planning, and it's a part you should take seriously.
No plane, no problem--right?
Wrong. Many dive destinations offer a variety of activities below and above the water. In the Hawaiian Islands, for example, you could dive in the morning and spend the afternoon 10,000 feet above sea level at the crater of a volcano. Most divers wouldn't even think about boarding a plane so soon after diving, but many don't think twice about heading up a mountain to enjoy the view.
Consider this: The cabin of an airliner is usually pressurized to the equivalent of between 2,000 and 8,000 feet--even if the plane's cruising altitude is 30,000 feet or more. So if a pressurized equivalent of 2,000 feet is enough to cause post-dive health concerns, a 10,000-foot mountain poses as much, if not more, of a risk.
Also consider the trip home when you're diving by car. Divers sometimes drive through mountain passes or higher elevations to access a dive site. The altitude shift that caused no problems on the way to the site can do exactly the opposite on the way home at the end of the day. If you know that you'll be driving through a mountainous area, or any area that causes you to experience a change in altitude, be sure to factor the altitude change and the subsequent considerations into your overall plan. If you're going to an altitude higher than the highest pressure of an airliner cabin (8,000 feet), wait at least 24 hours after diving.
In whatever form it comes, the bottom line is that altitude exposure is altitude exposure. There is no dodging the considerations they require, and ignoring them significantly increases your risk of being injured. So remember to keep your feet on the ground after you dive--if only for a little while.