Low Air Alert Similar to Structural Firefighting SCBAs

[FireDiver443]

My SCBA at work has an audible signal (used to be a bell, now it's vibra-alert) that activates when bottle gets to 25%, indicating it's time to stop playing with the fire and go get another bottle. It would seem, for recreational diving, if you started your dive at 3000-3200 psi, your system would activate at roughly 750 psi, allowing you to begin your ascent, do your safety stop and get back to the boat with the magic 500 psi.

I don't use an AI computer, so I don't know if this is a feature that's already incorporated in some way.

I suppose the down side would be that folks would stop looking at their SPG periodically throughout the dive, coming to rely on the low air alert to know when it's time to head topside.

John

[HowardE]

My SCBA at work has an audible signal (used to be a bell, now it's vibra-alert) that activates when bottle gets to 25%, indicating it's time to stop playing with the fire and go get another bottle. It would seem, for recreational diving, if you started your dive at 3000-3200 psi, your system would activate at roughly 750 psi, allowing you to begin your ascent, do your safety stop and get back to the boat with the magic 500 psi.

I don't use an AI computer, so I don't know if this is a feature that's already incorporated in some way.

I suppose the down side would be that folks would stop looking at their SPG periodically throughout the dive, coming to rely on the low air alert to know when it's time to head topside.

John

I have an AI computer, and it has 2 audible alarms. One you can set at the "turn point" (1000 PSI for me) and another set at "out of gas" (I keep this one at 500 psi)

[do it easy]

The old J-valves did something like this, although instead of a bell, it would just increase breathing resistance.

[Charlie99]

You could always do what some military divers do when diving in conditions where they either can't see the SPG, or it is too dangerous to use a light to see the SPG.

Simply dive a set of doubles with the isolator valve shut. When you run out of air, open the isolator valve to equalize tanks, and then shut it again. You are now at 1/2 of your gas supply. The next time you run out you will be at 1/4 gas supply.

Somehow, I don't think this method is going to catch on in recreational circles.

Charlie Allen

[james croft]

There were various first stage honker alarm and also valves that had a pendulum type device that would strike the side of the tank and alert the diver to a low air situation before SPGs became standard equipment. They were good for scaring fish and were not very popular. I am unaware of military divers using isolater valves for doubles. All I have ever seen were solid J-valve manifolds or single j-valve 80's. J valves are standard fo the military.

[Wildcard]

The old SP mk7s viberate at 700 psi. Not a new idea.

[wedivebc]

I have an old tank valve somewhere around here that was made by aqualung back in the 60s. It has a clapper that rattles the inside of the tank when the pressure got low.
Not a new idea I'm afraid.

[scubafanatic]

My SCBA at work has an audible signal (used to be a bell, now it's vibra-alert) that activates when bottle gets to 25%, indicating it's time to stop playing with the fire and go get another bottle. It would seem, for recreational diving, if you started your dive at 3000-3200 psi, your system would activate at roughly 750 psi, allowing you to begin your ascent, do your safety stop and get back to the boat with the magic 500 psi.

I don't use an AI computer, so I don't know if this is a feature that's already incorporated in some way.

I suppose the down side would be that folks would stop looking at their SPG periodically throughout the dive, coming to rely on the low air alert to know when it's time to head topside.

John

....another 'solution' for the problem you pose would be for one to dive a low-end, unbalanced 1st stage regulator... ie. Aqualung Calypso / Mares R2 / Oceanic Alpha 8 are a few examples of current production, entry level regs that are the typical unbalanced piston 1st stages...their advantage, as it were, is breathing resistance begins to increase at low tank pressures...achieving the 'goal' you seek.

Karl

[SparticleBrane]

Learning good gas management might be a better idea in the long run.

[FireDiver443]

I'm with you 100% that good gas management is the best practice. I threw this out there more because I've had many divers and instructors over the years ask me about the SCBAs I use at work and how they're different from scuba. Since this alerting system has been incorporated into SCBAs since they were introduced, I was hoping someone would pop up with a "why this hasn't been done."

When at work, I use the rule of thirds. If I've done it right, my SCBA doesn't go into vibra-alert until I'm already headed for the exit. But let's face it... a structure fire is often the ultimate zero viz scenario. There's no way you can even see your console a lot of the time because of smoke conditions. That's one of the reasons SCBAs are equipped now with an in-facepiece HUD.