Why Dive a Computer? – Safety
SKubaSteve - 11/22/2013 3:00 PM
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Last week I listed the following reasons I dive a computer and discussed the first one:
Increased dive time Safety The tables seem like they were designed to sell dive computers Gas mixture programming Dive logging Convenience

In this week’s exciting episode of ‘Why Dive a Computer?’ we’ll explore some safety considerations related to SCUBA diving with a computer.

Here is a summary of SKuba Steve’s dive computer do’s and don’ts!
Diving Computer Do’s Plan your own dives Tell your computer the truth Diving Computer Don’ts Don’t perform decompression (or Nitrox) diving without proper training Don’t share dive computers

Let’s get to it…

I’m not going to try to convince anyone that diving a computer is safer than diving the tables. I will let people who know a lot more about algorithms and other inexplicable math have that debate. What I want to talk about is how I try to keep safe while diving a computer.
Dive Planning

I always plan my own dives. Even with a tour group. I listen to the dive plan and then I work out what that means to me on my computer. You can absolutely plan and profile your dives using the tables. Having said that, I’m not great at math; and doing word problems on a crowded dive boat while everyone around you is shuffling about trying to get ready, put their gear together, grab a banana or take that last trip to the restroom…well it’s just hard for me. Maybe you don’t share this problem but I don’t think I’m alone.

Dive computers today have planning tools that allow divers to review dive plans and make adjustments to depth, interval and length of dives to account for other dives either already completed or planned later in the day.
The Truth Shall Set You Free

There is a school thought that suggests that one of the benefits of diving Nitrox is that, by diving Nitrox and planning as if you’re on air, that you will achieve a ‘added margin of safety’. Okay, this is not a Nitrox course so I’m not going to go into the specifics of Nitrox diving but…

Diving one gas and setting your computer to another is a bad idea. There are limitations for every dive gas and they are not equivalent. If your dive computer thinks you’re diving air it cannot provide information that will help keep you safe if you’re actually diving Nitrox.

The saying ‘Garbage In Garbage Out’ is as true for dive computers as it is for other computers except in this case Garbage In = DCS Out.

If you want a ‘extra margin of safety’. Plan shallower, plan shorter, plan conservative surface intervals, stick with your buddy, plan your dive with your desired margin of safety and dive your plan. Easy.
For the Curious

If you prepared to go on faith here just skip down to “Don’t Go Deco” but if you aren’t quite convinced…

The truth about what is called a ‘extra margin of safety’ is that by diving the air tables but breathing Nitrox you will be absorbing less Nitrogen (N2) than you would diving on air. The math – assuming equal depths, if you dive a 32% Nitrox mix the amount of N2 is 68% vs. the 80% N2 in normal air so you absorb less N2.

68% N2 (Nitrox) something that is completely within the control of the diver during the planning phase of the dive and does not require using one gas but planning for another. It’s simply unnecessary.

This is where it goes from unnecessary to bad planning. Because Oxygen (O2) becomes toxic at depth, the higher the concentration of O2 in your breathing gas, the shallower your maximum operating depth (MOD) must be. Some common MODs based on O2 percentages (1.4ppO2 – for Gas Math Maniacs) are shown here:
Air (20%): 187 Feet (Recreational Divers: Please stay within the scope of your training or 130 feet whichever is shallower.) N2 (32%): 111 Feet N2 (36%): 95 Feet

So you see now that since the recreational limit for scuba diving is 130 feet and diving Nitrox can substantially reduce your maximum operating depth. As a diver, if you plan around air (maximum operating depth of 130 feet for recreational divers) but dive Nitrox which has a shallower maximum operating depth, you put yourself at risk of oxygen toxicity. This is especially true if you incorrectly set your computer which then cannot provide any warning that you are nearing the maximum operating depth (MOD) for your breathing gas and can lead to serious injury or death.
Don’t go Deco

While I would not call myself a ‘Tech Diver’ I did get through Advanced Nitrox (mixes >40%), Decompression and Extended Range and enjoyed every minute of it – I had to take a break at Trimix/Heliox as tank fills tend to get a little pricey (~$300/fill/set of doubles at the time I was taking the class).

And here’s the point…

Many of our recreational computers will dive decompression profiles. No matter how many times you read your owner’s manual – Decompression diving (deco) is not a recreational diving activity and should not be attempted without proper training. Always dive within the limits of your training. In my experience, no piece of equipment is equivalent to proper training. A deco dive computer does not make you trained in decompression diving and a bottle of Spare Air does not make you a trained solo diver.

Oh… and your dive buddy’s training is not your training.

Editor’s Note: It occurs to me as I am proofing this that many dive computers will also dive Nitrox and other gas mixtures and not all recreational divers are trained to dive Nitrox. The same principle applies here as well. Stay safe and dive only within the scope of your training!
Sharing is Caring – but not Sharing Dive Computers

Two things I’ve heard that are like barnacles on a chalkboard:

‘It’s okay my buddy has a computer…’

‘It’s okay the dive master has a computer…’

you never go deeper than your dive master (or buddy) and… you are breathing the same gas as your dive master (or buddy) and… you don’t stay underwater longer than your dive master (or buddy) and… you don’t get separated from your dive master (or buddy) and… you can predict the future… and it’s free of any unforeseen events

Seriously dive buddies… let’s not do this okay? It’s not safe. Plenty of dive accidents are the result of divers putting themselves at risk in ways that may have seemed like a good idea at the time but resulted in injury. Do not dive your buddy’s computer. Even though I’m a card-carrying member of the dive computer fan club – if you don’t have one – dive the tables.

Our safety as individual divers and the reputation of our sport is dependent on each of us being responsible to take care of ourselves. While SCUBA is definitely a buddy sport, each diver must be able to operate independently.

Reading through this again it seems like I’m trying to convince people not to SCUBA dive with computers. Nothing could be further from the truth! I love my dive computers and I’ve been using them my entire dive career. There are serious considerations that come up when using these instruments to help keep us as safe as possible underwater.

Just to recap…
Diving Computer Do’s Plan your own dives Tell your computer the truth Diving Computer Don’ts Don’t perform decompression (or Nitrox) diving without proper training Don’t share dive computers

Okay, this has been a bit of a serious post so I promise next week’s episode will be on the lighter side!

Please add your comments other safety points you think about while diving your computer or how your computer helps you increase your safety under water!

The surface interval’s over … get out there and dive!

SKuba Steve

© 2013 Stephen Krausse – All rights reserved.