Inadvertent gas switch on Shearwater?

[stuartv]

I was out on a 6-pack weekend before last. We did one long dive. After everyone was out and getting out of their gear, one of the guys said something like "hey, my Perdix did a gas switch on its own!" Before I could even say anything, another guy on the boat said "yeah, mine did that to me once last year."

In both cases, they attributed it to having other things on their arm or hand that accidentally pressed the Perdix/Petrel buttons just right to do a gas switch without the diver knowing it.

I was surprised it happened. I was really surprised when someone else chimed right in that it had happened to him, too. Especially since there were only 6 divers (counting me) on the boat. 5 tech divers and one 1 rec diver. 4 of the 6, I think, using a Petrel or Perdix. And I used to have a Petrel 2, but sold it (but that never happened to me).

Anyone here have that happen before?

Maybe that's a reason to design dive computers with the buttons on the front (like the Ratio iX3M or HW OSTC 4) or top (like many puck-style Rec computers)?

 

[The Chairman]

You need to be careful with any PDC and keep checking it. I've found my PDCs in gauge mode a few times and once even in free diving mode. It hasn't happened on either of my Petrel IIs, but if you're careless anything can happen.

 

[rhwestfall]

depending on the forearm clutter, my state/schedule has activated the buttons on my Petrel. I wear both on the right, and "need" the slate there as I am left handed. Prefer PDC on right as left has light & compass as well as operates inflation....

 

[tbone1004]

what Bob said, I have had my Petrel inadvertently go to the right because a wrist slate contacted the piezo, but never make a gas switch because that requires both sides of buttons.

 

[boulderjohn]

It happened to me last weekend. There is no possibility that it was a mistake on my part, as you will see in the explanation.

I had two gases programmed in--a bottom gas and 100% O2 for decompression. We were not actually doing decompression, though--I was working with students on skills in shallow water. I was carrying two computers--a Perdix and a Petrel, both up to date on firmware. I checked them fairly early in the dive--no problem. I was not overly concerned because of the shallow depth with double tanks. Eventually I glanced at a computer to check depth and saw a high PPO2 warning. What??? I saw that it had switched to the 100% O2, and it was justifiably freaking out at my depth. I looked at the other computer and, sure enough, it, too, had switched to the 100% O2 and was freaking out. I have had the buttons pushed accidentally by the cuff of my dry suit, but not two computers on two different wrists at the same time.

 

[stuartv]

It happened to me last weekend. There is no possibility that it was a mistake on my part, as you will see in the explanation.

Wow! Just... wow.

Do you worry at all about the possibility of that happening on a real deco dive? I mean, if both computers switched to O2 early in the bottom portion of your dive, you would end up with the computers thinking you have WAY less inert gas in your tissues than you really did. At that point, you would pretty much have to fall back to something like a written plan or Ratio Deco. Or a buddy's computer.

Again I wonder...

Maybe that's a reason to design dive computers with the buttons on the front (like the Ratio iX3M or HW OSTC 4) or top (like many puck-style Rec computers)?

Funny how you never hear about this in "what computer should I buy" threads and people are piling on with the "Shearwater is The Best" posts.

I was thinking the OSTC 3 was my personal #1 choice in a tech computer right now, but it has side buttons that look even more prone to accidental presses than the SW's. I guess my list of personal options is now reduced to the Ratio, the OSTC 4, or maybe a ScubaPro H3 w/AI.

I have never had any accidental button presses on my SeaBear H3. But, they are at 45 degree angles, so I guess it could happen. However, they are pretty stiff and the computer is pretty small and low profile, so I think it's at least a LOT safer from accidental presses than a Shearwater or OSTC 3.

 

[Stoo]

Weird... it takes four moves on alternating sides to change a gas... Seems unlikely to happen by accident. I have found my Petral speaking poorly too me on occasion, but it's always do to operator error... usually left on O2 from the previous dive.

 

[stuartv]

My recollection is that if you're at a depth where you would change gas, it prompts you and then it only takes 2 button pushes to switch. E.g. if you have O2 programmed and you ascend to 20 feet. As boulderjohn may have done. Am I misremembering that?

Of course, that said, I guess that does make it pretty unlikely that you would change by accident during the actual bottom portion of a real dive.

Side note: I was reading the OSTC 4 manual today and noticed that it has a nice feature for gas management. You designate one gas as your "first" gas. If you only have 1 gas programmed, it's automatic. You also program some gases specifically as "Deco" gases. I think if you only have 1 gas that is not a deco gas, its selection as "first" is also automatic. Anyway, the point is, if you finish a dive on O2 and forget to change your computer back to your back gas, with the OSTC 4, it doesn't matter. When you start the next dive (assuming you're using the same gases), it will automatically switch to the "first" gas at the start of the dive.

I have done just what you said (started a dive with my computer still set to O2), so I thought the OSTC feature sounded pretty cool.

 

[stuartv]

Side note 2: The H3 prompts me to switch to O2, even at the start of a dive, until I descend past 20'. That's a bit annoying.

Side note 3: When the H3 prompts for a gas switch, it's just one long-press on one button to do the switch. Even easier than the Petrel/Perdix.

 

[Stoo]

My recollection is that if you're at a depth where you would change gas, it prompts you and then it only takes 2 button pushes to switch. E.g. if you have O2 programmed and you ascend to 20 feet. As boulderjohn may have done. Am I misremembering that?

I have mine here... from the dive position...

1st left...Turn off... which doesn't happen when your diving, so we don't count this one...
2nd left... Select Gas (1)
1st right... Gas choice screen (2)
3rd left... Move to new gas (3)
2nd right... Select new gas and then it changes back to dive screen. (4)

Four moves... I sometimes have mine kick into the secondary screen when the right side (I wear it on my left arm. it's a camera thing...) bumps up against my cuff ring.

I suppose in fairness, if you were wearing this on your right arm, it could switch to the Select Gas screen, which certainly gets you on your way to a change, but you still need three alternating side pushes to complete the change.

Not saying it isn't possible, but it seems unlikely.

Maybe it would help to flip the screen around so that the buttons are up at the top of the device... less likely to push them?