Driving Over a Mountain After Diving

[matt215]

I'm going to do a open water check out dive with my dad who is getting certified this weekend. My concern is that after the quarry dive I will have to drive over a mountain that is 2100 ft at it's highest point. The dive at the quarry won't be deeper than 35 - 40 ft. Would driving over this mountain be an issue? I would probably be driving over it about 3 hours after getting out of the water. I'm thinking if diving nitrox to reduce risk. What do you guys think?

 

[String]

I'm going to do a open water check out dive with my dad who is getting certified this weekend. My concern is that after the quarry dive I will have to drive over a mountain that is 2100 ft at it's highest point. The dive at the quarry won't be deeper than 35 - 40 ft. Would driving over this mountain be an issue? I would probably be driving over it about 3 hours after getting out of the water. I'm thinking if diving nitrox to reduce risk. What do you guys think?

3hrs after an extremely shallow dive and only 2100ft. No problem.

 

[D_B]

Also, your ascent rate is likely going to be very low driving up

 

[HBO MD]

Sorry, but yes, it could in fact be a problem. While diving to around 30ft or so is still considered relatively shallow, the fact is that you do take up nitrogen, and at that height there is an approximately 10% reduction in barometric pressure.
I think your idea of reducing the risk by doing nitrox is a good one.
In addition, you may want to refer to the NOAA tables as this question has been asked before. I believe you'll need a minimum surface interval of about 3 hours before ascending.

http://www.ndc.noaa.gov/pdfs/AscentToAltitudeTable.pdf

 

[knotical]

The NOAA Ascent to Altitude table should be coupled with one of NOAA's No-Decompression tables
e.g. for air: http://www.ndc.noaa.gov/pdfs/NoDecoAirTable.pdf
for EANx32: http://www.ndc.noaa.gov/pdfs/nitrox32.pdf
etc.

Why? Because the pressure groups in NOAA's tables are not the same as those used by many recreational agencies.

 

[TSandM]

Sorry, but yes, it could in fact be a problem. While diving to around 30ft or so is still considered relatively shallow, the fact is that you do take up nitrogen, and at that height there is an approximately 10% reduction in barometric pressure.

HBO MD, considering that the NDL time at 30 feet is measured in hours, and that the average OW certification dive is about 25 minutes, how can this be true? A ten percent reduction in ambient pressure is equivalent to going from 33 fsw to 26, and you can do this at 60 fpm during the dive or at the end of it -- how can a reduction of ten percent done over several HOURS afterwards conceivably cause problems?

I know this is often stated. And I know that airplane travel is a bit different, because the ascent rate is so much higher AND there are depressurization risks. But to tell somebody they could get into trouble by driving up to 2100 feet several hours after some very short, shallow dives seems to me to be a bit Chicken Little-ish. Are there any papers to show that there really is significant risk from this?

 

[FritzCat66]

I had this issue come up when diving on the Kona side of Hawaii island, but then having to return to my place waaay over on the Puna side, near Kalapana. However, that was after a couple of deeper, longer dives. The most direct route home would have put me at some serious altitude over those big mountains, so we just enjoyed Kona for another 12 hours and drove the looong way around to get home, just to be safe.

 

[vladimir]

I'm going to do a open water check out dive with my dad who is getting certified this weekend. My concern is that after the quarry dive I will have to drive over a mountain that is 2100 ft at it's highest point. The dive at the quarry won't be deeper than 35 - 40 ft. Would driving over this mountain be an issue? I would probably be driving over it about 3 hours after getting out of the water. I'm thinking if diving nitrox to reduce risk. What do you guys think?

I think you can dive to 40 feet for 70 minutes on air (="G" group) and safely begin an ascent to 2100' immediately. I used the NOAA tables linked by HBO MD and knotical.

 

[JohnB47]

As TSM observed, if the dive is only 30 minutes or so at less than 40 feet, there is no problem - no surface interval is needed. The NOAA tables referenced in the posts by HBO MD and knotical show that even for 80 minutes at 40 feet, no surface interval is required. However, if the dive were for 100 minutes at 40 feet, a significant surface interval would be necessary. If anyone in this situation has any concern about it, they should use the tables and do the math.

 

[HBO MD]

Hi TSM,
You are completely correct. My point relates merely to being vigilant when encountering altitude following a dive as matt215 is. Not all of the divers we encounter are as thoughtful.
As to being chicken little-ish, again you're spot on, but it's related to clinical cases of DCS which we encountered and outlined some years ago in Melbourne....
Weinmann M, Tuxen DV, Scheinkestel CD, Millar I. Decompression Illness: 18 Months Experience at the Alfred Hospital Hyperbaric Service. SPUMS J 1991; 21(3); 135-142
Further, the etiology is not merely a function of differentials in pressure as occurs with altitude exposure, but also of the time for off gassing which may be impaired in a number of situations, such as changes in body temperature during exposure, underlying injury, micro vascular disease etc.
My comments were made in that context and in order to provide another reference to the NOAA info.