Equipment My first out of air situation

[wdeutsch]

Interesting. And how did you determine it reads high by a "few hundred PSI" ?

Comparison to several other gauges that all agree with one another - both SPG, compressor output gauge, and another M8HA transmitter. I suppose it *could* be the one that's right, but then my oceanic M8HA transmitter would be reading several hundred pounds low. So, same issue.

 

[tursiops]

Comparison to several other gauges that all agree with one another - both SPG, compressor output gauge, and another M8HA transmitter. I suppose it *could* be the one that's right, but then my oceanic M8HA transmitter would be reading several hundred pounds low. So, same issue.

Thanks. Trying to understand. It is an offset of a few hundred PSI, so reads (say) 350 when it is actually 150?

 

[wdeutsch]

Thanks. Trying to understand. It is an offset of a few hundred PSI, so reads (say) 350 when it is actually 150?

I'd love any insight on it as well. I've surmised that it's an electronics issue of some sort, having to do with the calibration algorithm, but would be interetsted to hear your thoughts.

It reads about 500-600 PSI high on a full tank (AL80) and seems to keep roughly that ratio as the tank pressure drops - as though the issue is with the slope in a y=mx+b type relationship. But, it's not *exactly* that. There looks to be some amount of positive offset at low pressures. Of course, that's by comparison to other gauges, so the offset could be from those having non-linear responses too. I don't have a gauge that has sufficient accuracy and traceable calibration to compare against, unfortunately.

To be fully transparent, I haven't spent a lot of time trying to characterize it. As soon as I realized it was off that much and wasn't able to be recalibrated, I relegated it to pony use and haven't investigated more. If you're interested, I'm open to experiments. A little light science is always fun!

 

[tursiops]

I'd love any insight on it as well. I've surmised that it's an electronics issue of some sort, having to do with the calibration algorithm, but would be interetsted to hear your thoughts.

It reads about 500-600 PSI high on a full tank (AL80) and seems to keep roughly that ratio as the tank pressure drops - as though the issue is with the slope in a y=mx+b type relationship. But, it's not *exactly* that. There looks to be some amount of positive offset at low pressures. Of course, that's by comparison to other gauges, so the offset could be from those having non-linear responses too. I don't have a gauge that has sufficient accuracy and traceable calibration to compare against, unfortunately.

To be fully transparent, I haven't spent a lot of time trying to characterize it. As soon as I realized it was off that much and wasn't able to be recalibrated, I relegated it to pony use and haven't investigated more. If you're interested, I'm open to experiments. A little light science is always fun!

Hmm, I DO appreciate the y=mx+b comment...that is my native language. And the problem seems to be mostly m.
If it were mine, I'd first try getting an RMA from Huish before trying to fiddle the electronics:

"All returns, service, warranty, and exchanges require a return merchandise authorization (RMA). To submit a request for an RMA, please send the following information to TAC@huishoutdoors.com:​

​

1. Dealer/customer number (if available)
2. Product information and specifications (i.e. part number, model, size, color, serial number, etc.)
3. Reason for return"

Good luck! Always nice to have a trustworthy spare, instead of something you'd only use on a pony.

 

[scubadada]

Hmm, I DO appreciate the y=mx+b comment...that is my native language. And the problem seems to be mostly m.
If it were mine, I'd first try getting an RMA from Huish before trying to fiddle the electronics:

"All returns, service, warranty, and exchanges require a return merchandise authorization (RMA). To submit a request for an RMA, please send the following information to TAC@huishoutdoors.com:​

​

1. Dealer/customer number (if available)
2. Product information and specifications (i.e. part number, model, size, color, serial number, etc.)
3. Reason for return"

Good luck! Always nice to have a trustworthy spare, instead of something you'd only use on a pony.

That is a good idea, but I don't think Huish will service Aqualung transmitters, serial number prefix FC or FO rather than BM. Of course, nothing to lose by sending the information to Huish by email.

Question Post in thread 'Serial number prefixes on Pelagic Pressure Systems MH8A transmitters'

Mar 11, 2025

I communicated with Huish in January. They still service BM prefix transmitters except for flooding, which includes failure of the OPV. Here are 2 messages from Huish, the second to clarify flooding:

• scubadada

 

[Hatul]

i've not gone over every reply, but the question is what was the tank pressure when you got back on the boat. If the tank still had air it points to a blockage in the air flow, if the tank was empty it means you had a leak or the pressure gauge was bad.

And I agree with others that you should have immediately accepted the divemaster's octo when you found it hard to breathe.

 

[clownfishsydney]

My first thoughts from looking at the screen dump of the dive, a blocked intake on the valve. I have seen this happen before, person thought they were out of air but in fact the valve was blocked by rust particles. Did the OP check air pressure later or did anyone empty the tank and open it?

 

[tiacalypso]

I too would like to see the depth graph.

I don't use AI, but the air consumption graph does not make sense to me: it shows a remarkably constant slope, with ~100 bar used in ~35 min. This is regardless of changes in depth during decent or any changes in diver activity. For folks who do use AI: shouldn't there be greater variation in air consumption rate during decent and during the dive, and not a completely straight slope?

100 bar in say a 12 L tank is 1200 L - so the slope of the graph is 1200L/35 min = 34 L/m at 3 bar/20m. That equates to 11 bar/min on the surface: which is far lower than most experienced divers.

However assuming a more typical breathing rate for an inexperienced diver (say 22 bar/min) would empty a 12l tank in ~35 mins: close to what's seen.

As lizardland points out - I think the issue is with the AI/computer.

Cheers
Rohan.

I‘m an AI diver and my air consumption profiles are pretty linear.

 

[Subcooled]

Hello fellow divers. I'm a newcomer to the diving hobby. I got OW certified this year and have only 30 dives.

That's a nice amount of dives for the first year (or less).

At about 30 minutes from the start of the dive I checked my air and I had around 110 BAR.

Nice

At about minute 35 I noticed that taking a breath started to require a lot of effort

You spent 110 bar in five minutes??? Something does not add up.
Anyway, you are out of air. It has happened to me too, once unplanned at 60 ft.

I only had 3 BAR left . I immediately went to the dive master and gave him the out of air signal. He understood me and double-checked my computer. He offered me his backup 2nd stage,

Nice

but I didn't take it immediately, because I was still breathing (harder and harder, but still doable).

I have done the same thing myself, and it was not a wise choice. What if you would have lost contact with the dive master a bit later? You would have had absolutely no air!

You can indeed do a free swimming ascent from 60 feet, no problem, but it is always better to have one or two extra options.

I still had a strange feeling of uncertainty.

That is very wise unless, of course, it turns into panic.

We made it to around 5 meters and we started our safety stop.

A safety stop is completely optional. It is not a mandatory decompression stop. You might have continued directly to the surface, or if it feels better, made a short stop. Stopping, of course, gives a more gentle resurfacing experience to the body.

At minute 2 of the safety stop I had the same feeling again - taking a breath required a lot of effort and I was not able to take a full breath - clear sign the DM's tanks was running low.

Very low, actually.
WTF was he/she thinking allowing this scenario to take place?
PAID dive masters are supposed to be professionals.

I am loosing sleep over what actually happened.

Relax. I have ran out of air at 60 feet and the swimming ascent was quite nice. As the ambient pressure dropped, the relative overpressure in my scuba tank grew double upon ascent to the shallows and I could even waste some gas on a completely unnecessary safety stop.

Freediving 25m or 75ft is very much doable, too.

Maybe something blew up and all of my gas went out.

"Blew up" means bubbles and noise.

I was hearing bubbles going out.

Yes.

I don't know what to trust - what I heard or what my computer is telling me.

You should trust both. Hearing is more susceptible to misinterpretations but it is worth noting, though.

According to the DM it was sort of malfunction in the regulator, because it was due for a service.

Ouch! I once dove with a regulator that had not been serviced in five years and it was hard to breathe, but it still gave air on demand. On demand, indeed, as I had to suck. But it was different from the growing breathing resistance over a couple of breaths of an out of air situation.

I am confused

Me too

I am also wondering if I tightened the 1st stage to tank good enough. These were DIN tanks.

If you did not, you would have heard constant bubbles.

what can I do to reduce the risk of that happening again?

You can reduce the risks by relaxing.
These things sometimes happen and they are not a big deal if you are prepared and aware of your surroundings and situation

I am buying a set of personal regulators so that I can be responsible for cleaning and maintaining them.

 

[sena_akutsa]

At about 30 minutes from the start of the dive I checked my air and I had around 110 BAR. We were at 22 meters. At about minute 35 I noticed that taking a breath started to require a lot of effort, Looking at my computer I saw that I only had 3 BAR left We made it to around 5 meters and we started our safety stop. At minute 2 of the safety stop I had the same feeling again - By the end of it there was no air inside the tank.

According to my computer I lost my air in a very short time. I don't know what to trust -
According to the DM it was sort of malfunction in the regulator, I am also wondering if I tightened the 1st stage to tank good enough. These were DIN tanks.

View attachment 914044

Hello,
like others said, if there was an air Leak then you, someone else from your group, or the dive master would notice that.

I encountered 2 mechanical SPG that went bad in our club within 3 years,
but can say nothing about your "air integrated" transmitter reliability.
Still your graph looks like a mechanical problem encountered (like clogged valve).

....what bothers me more is:
your DM and You "emptied his tank" at the safety stop;
with which pressure the DM was planning to start the group ascend if you didn't run out of air ??
50 bar is more than enough for 2 buddies to stay more than 7 min at a safety stop depth, tried many times with a 12L tank.