DCS and altitude

[Fishdip]

So I have not had a issue with it yet (80) dives. But today I was thinking about the fact I go from living at (3773) to diving at (3900) to driving back to (3773). With that said my trip back home drops to (2956) 2-3 hours and it tops out at 5000 for about 5min. and then it is back to around 4000 for most of the trip tell arriving back at the (3773). What is the risk of DCS from hitting the 5000 feet? Dose the fact I dive at (4000) lower the risk at (5000)? Or since I drop down to (2956) mean that I am not at a higher risk going back up?

 

[inquis]

By the time you pack up and actually get to 5000 ft, it shouldn't be an issue. Look into the Navy or NOAA tables for more details, but 1100 ft after a single-tank NDL dive or two isn't much of an ascent.

 

[Fishdip]

Its usually 3-4 dives each day. Sat/Sunday.

 

[Esprise Me]

@boulderjohn has written about this before. IIRC driving to altitude tends to be a lot safer than flying, both because of the gradual ascent and the absence of the (small but real) risk of loss of cabin pressure in an aircraft. But if you're doing repetitive dives with aggressive profiles immediately before driving to altitude, you may want to wait a bit longer before getting in the car.

 

[J-Vo]

@boulderjohn 's website with his articles.

Deep Adventure Scuba Colorado Technical Diving - For Those Looking to Take Diving to a New Level

 

[J-Vo]

I'm not avocating anyone else do this.

Yesterday I did a 275' dive with 140 minutes runtime at an elevation of 4600'. I was driving over an 8k pass 3.5 hours later.

 

[inquis]

Shearwater computers show the modelled tissue tension relative to ambient post-dive. After doing 4 NDL dives per day (close to Buhlmann+GF x/85 limits) Fri/Sat, then 2 the Sun morning before I left... tissues were still below ambient when cresting a hill 2500 ft above the dive elevation 1.5 hrs later.

 

[Akimbo]

@boulderjohn 's website with his articles.

John also has an excellent thread in the ScubaBoard Knowledge Base:

Info - Diving at Altitude

Diving at Altitude Diving at altitude demands adjustments to the procedures used at sea level. With moderate increases in altitude and with shallower dives, the differences can be minor, even minor enough to be ignored. As altitude and depth increase, the need for concern grows. There are three...

scubaboard.com

 

[boulderjohn]

I'm not avocating anyone else do this.

Yesterday I did a 275' dive with 140 minutes runtime at an elevation of 4600'. I was driving over an 8k pass 3.5 hours later.

Did you breathe oxygen on the way?

 

[boulderjohn]

@boulderjohn has written about this before. IIRC driving to altitude tends to be a lot safer than flying, both because of the gradual ascent and the absence of the (small but real) risk of loss of cabin pressure in an aircraft. But if you're doing repetitive dives with aggressive profiles immediately before driving to altitude, you may want to wait a bit longer before getting in the car.

I'm not avocating anyone else do this.

Yesterday I did a 275' dive with 140 minutes runtime at an elevation of 4600'. I was driving over an 8k pass 3.5 hours later.

I would like to give a more detailed explanation of these two posts.

It is extremely hard to say anything definitive about driving to altitude because there is no good way to measure such trips, which are all different, and because it has not been studied much at all. When one is flying, the ascent is very rapid. When one is driving, it can be like doing a staged decompression ascent. What jvogt describes is something I have done countless times, following the same route at about the same time after diving. For a full description of the dive, go to this thread. Here is a shortened version.

1. Begin with the understanding that both DAN and the US Navy say an ascent of 2,000 feet is acceptable at any time after a dive.
2. He took about an hour at the site to pack his gear before leaving.
3. He had been breathing pure oxygen underwater for maybe 40 minutes, and his fastest tissues had off-gassed beyond saturation for that altitude. That means that those tissues were on-gassing as he breathed the local air while packing his truck.
4. After leaving his 4,600 foot altitude dive site, he had an ascent of about 800 feet, which took about 15 minutes.
5. He then stayed at that elevation for about a 20 minute decompression stop.
6. He then climbed another 600 feet (to 6,000 feet) and then another slow climb, reaching 6,800 feet after about an hour of total driving from the dive site. Note that this is almost exactly the limit for an immediate ascent to altitude, but he did it over two hours, with the first hour decompressing at the site and the second ascending with a couple of decompression stops along the way.
7. He then did a 1.5 hour decompression stop as he drove, still at about the limit for an immediate ascent to altitude.
8. He then did a fairly rapid ascent of around 1,000 feet to the top of the mountain pass.

All that assumes he was just breathing the air as he drove. If it were me, I would be breathing oxygen for at least the first hour of that drive.

As you can see, that dive and that drive have characteristics that make it probably safer than most drives to that elevation, but there is no research to support it. As I said earlier, I have decided that this drive is safe enough for me, at least while breathing oxygen, but I will not tell you that it is OK to do it. That is a decision you have to make for yourself.

So what about your drive to altitude? You will have to analyze it the way I have analyzed mine, and then you will have to decide for yourself.

A final note: when I researched this, I talked with someone at DAN who told me that all ascents are not the same. Ascending from sea level to 2,000 feet has a greater impact than ascending from 4,600 feet to 6,600 feet.