Posted October 2nd, 2017, 12:00 PM
Last edited by omeinv; October 2nd, 2017 at 12:20 PM
From what I've been reading, going to the top of Mauna Kea is enough altitude that it's considered as if you are flying from the perspective of getting rid of nitrogen in the blood after diving. We have Kona on day 6 and Hilo on Day 7 of my upcoming Hawaii cruise.
You are correct that ascending to altitude after diving is a concern. However, given the time lapse between diving on one day and ascending to elevation the next, you likely have little to worry about.
Specifically the concern is decompression sickness (DCS) brought on by nitrogen in the blood or tissues expanding due to the reduction of ambient air pressure. Ambient air pressure drops as altitude increases.
Without using a dive computer, the recommendation from most SCUBA training agencies is to wait at least 18 hours after a single dive, and 24 hours after repetitive dives before flying (your case is a little different than flying, but you’ll see where I’m going here). The reason for the 24-hour recommendation is that it’s presumed at all residual nitrogen will be purged after a 24-hour surface interval. Since 24 hours is presumed to rid the body of all excess nitrogen, then after that interval you would be presumed back to your baseline, and thus not affected by altitude for DCS.
Assuming you’d be diving in the morning of day one, and doing the standard two-tank dive, you’d likely be completing your second dive by noon of day one. On day two, given the ship’s arrival time in Hilo, and the travel time to the top of Mauna Kea, if you didn’t have a 24-hour surface interval, you would be extremely close to it. Therefore, I wouldn’t hesitate to dive then go the next day. Adding to the safety factor is that Kona isn’t known for particularly deep dives.
You can stop reading here if you just want to know the answer to the question; because now I’m going into boring detail.
First, for flying after diving, the assumption is made that we’re talking about pressurized aircraft (e.g. commercial airliners). Regardless of the altitude the flight reaches, the plane’s normal pressurization is considered to be the equivalent of 8000 ft. The altitude of Mauna Kea is 13,803 feet.
Nominal air pressure at sea level is 14.7 psi. At 8,000 feet it’s 10.9 psi, and at 14,000 feet it’s 8.6 psi. This is important because it is that ambient pressure that is serving to keep nitrogen in solution, in your blood, and thus preventing decompression sickness. You may also notice that the pressure decrease slows as altitude increases; in other words the difference in pressure between sea level and 1,000 feet is greater than the difference between 10,000 and 11,000 feet. Most research in ascending after diving has focused on flying after diving, and thus tends to look at the 8,000 foot pressure. However, as the pressure drop that occurs lessens as you go higher, it’s likely safe to use the same limits for ascending to greater altitude. This is especially true considering that by the time you’re at altitude, you’ll be very near, if not past 24 hours from the end of your dive (again since, all excess nitrogen is presumed gone after 24 hours, additional altitude is not considered a factor).
All that being said, some people have issues at altitude anyway. I’ve lived in Colorado my entire life, and everyone here has some story of people from lower elevations not doing well at extremes. It’s popular here for tourists to drive to the high mountains (elevations similar to Mauna Kea) and experience mild symptoms of altitude sickness (headache, nausea, generally not feeling well). My concern is that given your planned itinerary, if you had issues with the altitude, you may think it’s DCS when in fact it’s just the altitude anyway. Some symptoms would overlap, but DCS would manifest some specific symptoms of it’s own presumably.
So, to wrap up (finally):
Given the surface interval between your dive and your arrival at altitude, you will be presumed to have ridded all nitrogen for your body.
You can ensure this is the case by limiting your depth to a moderate point, and thus reducing your nitrogen uptake.
If you want to add another layer of safety, and you’re trained to do so, pay the extra to dive on nitrox. Nitrox 32 has 14% less nitrogen than air. The less you have in you, the less time it takes to leave.