O2 Dummy Light

brockbr

So I was reading about the Meg Pool incident, and there a ton of great feedback including Dave Sutton's mention of standardizing HUD LED signal etc.

But this got me to thinking - One of the more reported "incidents" is the diver forgetting to turn their O2 back on when entering the water. This was the case for the Meg diver after a quick adjustment poolside, he re-entered the water with his o2 off.

This led me to think of an O2 dummy light. It could really be simple (I dive a CK and subscribe to the KISS ideology). Using a standard LP pressure switch (they can be had for literally a couple of dollars), why not design an LED at the end of a length of wire. The wiring would be stupid simple - A small battery is in-line. When the pressure switch is pressurized, the circuit closes and the LED is lit.

The LED would simply be mounted somewhere near the DSV. No LED, no Dive. There's only a couple of failure modes:

(1) - Faulting pressure switch. By default, most of the designs fault into a non-pressure state due to using a small diaphragm. This would keep the circuit open, thus no LED. No LED, No Dive.

(2) - The second failure mode would be a dead battery. Again, no LED, no Dive.

I've looked into the pressure switches on the market, and they range from 15 PSI up to 6,000 PSI. 150 would be fine coming off the LP of the O2 regulator. It is also very common to find these switches made with Viton materials for use in O2 environments.

This seems like something VERY EASY to build for WAY under $15. And if you screw it up, the default mode is No Dive.

This is by no means a replacement for knowing your pO2, or any other type of a crutch for training, but for a few dollars, it would be a great safety that wouldn't introduce more failure points (unless you count MTBF for the pressure switch itself, if it is even possible for it to completely leak gas).

Surely such a thing already exists and I just haven't found it on Google yet

Downtime

Wouldn't this have the same effect as low PPO2 alarms? The Hammer's (on my Optima) have a Heads Up display that alarm when the PPO2 is low, therefore if you jump in the pool without turning on your O2, once you breath your loop down below your set point you get a red flashing light, and if you ignore that, then it eventually vibrates. I believe other units have similar alarms or notification methods which will in effect tell you there is no O2 getting into the loop?

The rule is to know your PPO2 at all times (Thanks Dr. Pyle), and if the diver ignores this rule, I think they would probably ignore alarms on handsets and coloured blinking lights as well, regardless of what they are trying to tell you.

Maybe there is no such thing as a "Fool-Proof" rebreather.

Cheers,
Michael

jasondrake

I think it's a brilliant idea. I suspect lots of incidents have resulted from o2 cylinders being left closed.
A solution that's cheap, easy to fit and adds no real failure points/clutter/etc.

If someone builds one I'll buy two!

Padowan

Isn't this what the pressure gauges are for?

Personally, checking the pressure gauges is part of my descent checks, so I will see if the gauges have dropped significantly, indicating a presurised, but turned off valve.

I like the concept of a HUD light, though, although it's redicing an issue that really shouldn't be there for diving at this level.

__________________

Packhorse

If you forget to check that your O2 is on what make you think you will remember to look for the light?

__________________
There are no stupid questions, but there are a LOT of inquisitive idiots.

lizardland

Exactly.

__________________
Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you?

www.westons-cider.co.uk

Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler

brockbr

Actually, since it is directly in your field of view, and from a human interface standpoint, requires no action on the part of the diver to see, I think it stands an excellent chance of being noticed.

You can see *many* engineering examples of this in practice. HUD's in and of themselves prove the point - We all know we should know our pO2, but instead derive this information (to some extent) from our HUD's.

The MEG HUD tells you pO2, the KISS HUD (C2R/VR3) shows if you within .2 of setpoint. Some other HUD's simply show High/Low in some other manner. But all together, we use them because they are in our field of view.

Know your pO2, right?

If that is the mantra to be followed, why do we have HUD's? To simply excuse away a HUD and say "well, that's just for confirmation of my pO2 so I don't have to look"... Well, you can see that point spiraling into the abyss when you get the response "that's what this O2 LED is for"

(By the way, I am NOT saying we *only* derive our pO2 from our HUD, just that we use it as a tool that is *easier* to get to sometimes than our handset - Scootering is a good example for me. I check my pO2 every 2-3 minutes no matter what, but in the interim, I use my HUD to tell me it's close - Think "bang" situation when you might not hear it due to scootering)

I also think it's somewhat disingenuous to counter the point with "at this level, you shouldn't forget your O2". That is akin to saying "let's not try and prevent the accident since it shouldn't happen in the first place, even though we know is *does* happen more often than it should".

And Downtime, I like the HH setup, but not all of us have it I was trying to think of a simple, fault-tolerant way of adding this type of alarm to any existing rebreather.

lizardland

I think it comes down to the old good/bad alarms scenario. Does the light off mean your O2 is on or your light is broken? So now you need something to differentiate between the two states... two lights, colour change, etc.

Or you could just check the tank valve...

Isn't this yet again a case of pouring technology on bad technique?

__________________
Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you?

www.westons-cider.co.uk

Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler

brockbr

That's was a funny way of validating my design - Thanks!

Dave Sutton

Little technical V/S human factors lesson:

CIS Mk-5P does not have gauges for diluent and 02 pressures. It uses pressure transducers and the outputs are monitored and displayed by the computer system on the brick (chest display).

The system requires both 02 and diluent sources to be ON and contents pressures within limits before it allows the system to continue thru it's BITS (built in test system) routine that is done during system boot-up and log-on. It's a self-measured variable done as part of the start-up checklist. No 02 or Dil? No startup. Simple, eh?

NONE of this prevents a Nobel Prize winning diver from doing that and then after the checklist is done, from *turning off the 02 vave* before a dive and then dying in waist-deep water in a Florida cave-pool because he forgot to turn it back on........ and that is with a brilliant man diving what is inarguably the worlds most sophisticated rebreather, with the best HUD that has ever been designed.

So.... add alll the stuff you like. A determined person will still manage to kill himself. With all due respect (and from someone who is not a Luddite from a design standpoint), the proposed system seems like an ingenious solution to a nonexistant problem. Monitor PP02... it'll catch the off-valve situation.


Best,

Dave

.