Diving at Altitude Air vs. Nitrox

[Daylonious]

Have a question for my more experienced divers out there:

I'm planning on doing a dive next weekend at Valhalla Missile silo near Abilene. I believe it's above 1000' so that makes it an altitude dive.

I'm debating whether using a set of 90cf steel doubles (straight air), or just bringing a few tanks of EAN36 would be better.

This is what I was hoping I could pull off:

4 dives past 100' in 6 hours - staying within NDL.

Here's my questions:

1) does doing 4 dives look reasonably safe to do in the time I have (10am-4:00pm or so at the silo)

2) I've been told this is considered an "altitude" dive - how does that affect my dive plan? I understand it shortens my bottom time, does it shorten it to the point where diving nitrox is pretty much the only way to go?

3) should I just skip the doubles and bring a few al80 tanks of EAN36 to do the 4 dives?

4) Are 4 dives pushing it "at altitude" so I should back off to 3?

5) brink a pony bottle of o2 just in case I blow a plan?

Thanks!

D.

 

[rhlee]

At 1000ft, it's not much of an effect. For example, an actual depth of 100ft has a theoretical air depth of 103ft. 130 is 135. I was told in my altitude class (at lake tahoe alt ~ 7000ft) to limit repetitives dives to 2 a day, but I'm not sure how closely that is followed. FWIW, I was told that the way to do dive planning with nitrox at altitude is to figure the EAD of your mix first, and then use that to index into the altitude conversion. Not sure if it makes much of a difference if you work it backwards, but that's what I was told.

2) I've been told this is considered an "altitude" dive - how does that affect my dive plan? I understand it shortens my bottom time, does it shorten it to the point where diving nitrox is pretty much the only way to go?

 

[TRIG]

Number of things to consider, one is ;

If you are using 1.4 for PO2, the MOD for 36% is 95 ft

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[Rick Inman]

I'm debating whether using a set of 90cf steel doubles (straight air), or just bringing a few tanks of EAN36 would be better.

What's your buddy diving?

 

[texdiveguy]

I think I can shed a few answers to your questions. This site is very demanding in terms of its physical challenges---- just getting in and out of the site with your gear is a chore (doubles NOT recommended!!) You will be transversing some 4 flights of stairs not to mention the 3 story decent from the entry into the silo chamber to the dive platform (which you will do fully kitted and going down a steep set of stairs backwards). Most folks only get in 2 dives over the outing. Water temp is 58f and actual depth is approx. 112ffw to the debris field at the silo bottom,,,,because it is at slight altitude the physlc. depth is around 124ffw. In order to do a nitrox dive in this setting you would need an EANx of less than 32 at the depths you mentioned in your pre-planning. Most divers use air and single tanks. Many safety considerations beyond those of normal sport diving are to be considered when planning an EANx dive at even slight altitude. Emerg. O2 will be on site and the DMs will keep it handy for sure.

 

[Daylonious]

Texdiveguy - thanks for explaining the site to me!

Okay then, sounds like doubles are out. It's enough of a workout humping them from the dive platform to my car at CSSP. Going down 3 stories and multiple stairs.. (well, not the going down part, it's the going UP part at the end of the day that would probably do me in)..doesn't sound like a picnic.

What are the major considerations for diving EAN at this altitude?

2-3 EAN30 AL80's sounds like the way to go - sounds physically strenous and very cold (at least to a brazillian) - the extra oxygen would be a nice offsetter.

D.

I think I can shed a few answers to your questions. This site is very demanding in terms of its physical challenges---- just getting in and out of the site with your gear is a chore (doubles NOT recommended!!) You will be transversing some 4 flights of stairs not to mention the 3 story decent from the entry into the silo chamber to the dive platform (which you will do fully kitted and going down a steep set of stairs backwards). Most folks only get in 2 dives over the outing. Water temp is 58f and actual depth is approx. 112ffw to the debris field at the silo bottom,,,,because it is at slight altitude the physlc. depth is around 124ffw. In order to do a nitrox dive in this setting you would need an EANx of less than 32 at the depths you mentioned in your pre-planning. Most divers use air and single tanks. Many safety considerations beyond those of normal sport diving are to be considered when planning an EANx dive at even slight altitude. Emerg. O2 will be on site and the DMs will keep it handy for sure.

 

[texdiveguy]

PM send to you.

 

[Dive-aholic]

texdiveguy hit it on the head. Valhalla is at about 2500 feet above sea level, so there are some considerations as far as MOD. It's also recommended that only 2 dives per day be done at altitude, 3 may be considered when training. To the depths of the silo, I'd stick to 2.

This site is extremely demanding, not only up, but down as well. The stairs to the water are extremely steep. It's hard enough to walk up and down them with a single tank on your back, never mind doubles. There's also not much to see in the silo. Two dives should be more than enough to see all there is to see. Valhalla is a BTDT dive. Go do your 2 dives, buy the t-shirt and tell people about it. Most will think you're a little off.

Here is some information and some photos of my trip to the silo last year. Make note of the stairs, stairs, stairs, stairs, stairs.........

Have fun on your dive!

 

[pholife]

why not strap the tanks to you your side and have an easy walk down with the tanks in hand?

 

[DivemasterDennis]

A dive at 1000 feet is an altitude dive, but with minimal impact on planning Planning a dive from 80 to 100 feet, you should add 3 feet to actual depth for dive planning purposes. Over 100 feet, for a safety margin, add 5 feet. This is important in considering using EANX 36, which has a maximum safe depth of about 95 feet to keep your pp of 02 at or under 1.4. At 90 feet, very slight variations in depth will put you over and under the max depth, so with your dive plans, I would use air or else EANX 32, which will give you an additional depth safety margin down to about 112 actual feet even factoring in an altitude adjustment. As to "can I do 4 dives" in the time alloted, depends on time at depth and duration of dives. What a great opportunity for you to work some multi-level repetitive dive profiles on your RDP. That is what you should do. Plan you dives.
DivemasterDennis