0:00
90 m down on an unknown shipwreck
0:05
and one of my oxygen cells starts
0:09
At this depth, there's no quick way up.
0:12
Your rebreather is your life support and
0:14
mine was telling me that something was
0:16
very wrong. I'm Dom Robinson and in this
0:20
video I'm going to walk you through
0:22
exactly what happened during this dive,
0:24
how I detected the failure, the
0:27
decisions I had to make, and the
0:29
procedures that got me back to the
0:34
Because of course, this is the reality
0:36
of this sort of diving. Equipment can
0:38
fail and does fail. And when it does,
0:42
you've got to make decisions. And those
0:44
decisions can be the only thing between
0:46
you and disaster. So let's see what
0:50
happened. But first, let's have a look
0:52
inside my rebreather. So this is the
0:54
clever bit. This contains all the
0:56
electronics and also has three of these
0:58
oxygen cells. And what they do is they
1:01
measure the partial pressure of oxygen
1:03
in and around here in the mixing chamber
1:05
before it gets supplied to me to
1:07
breathe. So they're absolutely crucial.
1:10
And this is one up close. They don't
1:12
look like much, but you can see they're
1:14
individually serialn numbered. They've
1:16
got dates on them. They do have a finite
1:18
life, though, and the recommendation is
1:21
normally 18 months. This one was just
1:23
over 12 months old, and I'd had a great
1:26
year of diving with it, so I wasn't
1:28
expecting it to go wrong. I'd also
1:30
completed the pre-dive check, which
1:32
consists of calibrating the oxygen cells
1:34
against 100% oxygen. All three cells for
1:38
this dive had gone through that
1:39
absolutely perfectly. So once again,
1:42
there was no indication that something
1:44
was going to go wrong. They were all
1:46
fine all the way through the descent.
1:48
And as you can see here, although I've
1:50
not done a linearity check per se, you
1:52
can see that they've all shown that
1:54
they're performing well outside the uh
1:56
set point of 1.3. And even for the first
1:59
10 15 minutes on the bottom, everything
2:02
was absolutely fine. For those who were
2:04
unfamiliar with the AP Inspiration
2:06
handset, you can see it in the bottom
2:08
left hand side of my screen. and the the
2:10
top row with the three numbers 1.3 1.4
2:14
those are the oxygen cell readings. So
2:16
the the P2 and as you can see at the
2:19
moment they're about 1.3ish
2:22
occasionally the middle one is flicking
2:23
up to about 1.4. Now the way that a
2:26
rebreather works is it uses something
2:28
called voting logic. So it takes the two
2:31
cell readings that are closest together
2:34
and assumes that those provide the P2
2:37
and that P2 will be used to do two
2:39
really important things. The first thing
2:41
is control decompression. But the really
2:44
important one is that controls the
2:47
injection of oxygen. So provided that
2:50
two cells are right, it is going to
2:53
everything is going to be okay. The
2:55
nightmare scenario is when only one cell
2:58
is right and the voting logic uses the
3:01
two wrong cells and that can be super
3:03
super dangerous. So what as a diver you
3:06
have to do is decide whether you have
3:09
one cell that is okay or you have two
3:11
cells that are okay. Now obviously what
3:14
you really want is you want three cells
3:15
that are okay. And that is the situation
3:18
most of the time. But on this dive, I
3:21
started to notice that there was a
3:24
problem. I started to see that one cell
3:26
was reading a bit higher than the other
3:28
two. And that's when I started to become
3:30
a little concerned. Now, this does
3:32
happen. So, it wasn't a huge concern,
3:35
but I could clearly see that two cells
3:38
were pretty similar, pretty nailed
3:40
together, and the other one was starting
3:42
to just be a bit higher. You can see it
3:45
here. It's the middle cell. Uh, it's
3:47
currently about 1.42. 42. The other ones
3:49
are about 1.3 or thereabouts.
3:53
And this, of course, is where decision-m
3:54
comes into it because if you were to be
3:58
on a rebreather course, the instructor
4:00
would tell you if you see that a cell
4:02
fails, you should do a dealing flush,
4:04
you should consider bailing out and you
4:06
should have bought the dive. I'm sure it
4:08
won't surprise anybody who's watched any
4:10
of my videos and the kind of experiences
4:12
I had to realize that that isn't what I
4:15
am going to do. And let's talk through
4:17
that decision process. Well, the first
4:19
thing, of course, is that this isn't an
4:22
unsafe situation. I just have a cell
4:24
that is reading a bit higher than
4:26
another. So, that in itself is not is
4:29
not a huge concern. Even if the actual
4:32
P2 in this uh rebreather was 1.46. So,
4:35
the the one that's reading high is
4:37
correct. Once again, that isn't uh the
4:39
end of the world. The other thing, this
4:43
wreck is 45 mi offshore. I've spent a
4:47
lot of time and effort and frankly money
4:49
to get here and therefore I want to get
4:52
the most from myment. So unless it is
4:55
something that I consider to be
4:57
absolutely uh a safety issue, then I'm
5:01
going to stay doing you know what I'm
5:03
doing, which is of course continuing to
5:05
investigate the wreck. You may have a
5:07
different view on that. You may take the
5:08
view that I should have bailed out. I
5:10
should have aborted the dive. And you
5:12
know what? That's entirely right. If if
5:14
that is what you wanted to do, then of
5:17
course that is the absolutely perfect
5:20
solution. But of course, we live in an
5:22
imperfect world. And you know, it's part
5:26
of part of doing this kind of diving is
5:28
you make those make those decisions and
5:30
you got to live with the consequences.
5:32
And what you can see has happened here
5:34
now is this is a bit later on in the
5:36
dive. I've actually come back to that.
5:38
Um, well, whatever it is, I've seen you
5:40
maybe a water filter that perhaps. And
5:43
what you can probably hear every now and
5:44
again is a beep. And the reason you can
5:46
hear a beep is cuz we've now got the the
5:49
alarm. So, the inspiration will alarm if
5:53
there is a difference of more than 2
5:56
between a single cell and whatever the
6:00
two voting cells are. So in this
6:02
particular case, there's a cell the two
6:04
voting cells are about 1.36 and 1.27.
6:08
So the the the P2 used by the unit is
6:15
that sort of thing. So whenever the
6:17
middle cell goes more than 2 bar above
6:20
that, that's when we're going to get the
6:21
alarm. And what you get is you get an
6:23
audio alarm, you get a flashing alarm on
6:26
the head-up display and get the uh alarm
6:29
on the handset as well. loads of
6:31
indications that something is wrong. You
6:33
can do is you can suppress the alarm by
6:36
pressing and holding one of the buttons
6:37
for two seconds. And what that does is
6:40
just stops the alarm going off for a
6:43
period of time. I think it's five or
6:44
possibly 10 minutes. Going back to my
6:47
decision making process, I've been
6:49
watching this single cell rise to the
6:52
point that it's now started to alarm.
6:56
Going back to my decision- making
6:57
process. So, I'm evaluating the factors
6:59
here. I've potentially I've got two bad
7:02
cells and one good cell, in which case
7:04
the good cell is reading 1.5 P2. That is
7:08
not the end of the world. It's extremely
7:10
unlikely to kill me, although it's not
7:13
particularly ideal. Of course, what I do
7:17
believe is that I know exactly what's
7:18
happening, which is I've got one bad
7:20
cell. I've watched the one cell track
7:23
away from the other two. Potentially, of
7:25
course, it could be that um two cells
7:28
have failed at exactly the same time.
7:30
That's just really really unlikely,
7:33
which is why I'm carrying on with the
7:35
rest of the dive, as you can see. And
7:37
you can see that the the middle cell,
7:39
it's still, you know, it's not it's not
7:42
brilliant. It's not performing
7:44
particularly brilliantly, but you
7:46
probably see the uh the flashes and
7:47
lights. I'm I'm in and around the area
7:49
of the shot line, in around the area of
7:51
the strobe. So if I absolutely needed to
7:53
bail out or needed to come back, I would
7:55
be in a great position to do that. And
7:57
in fact, I spend the rest of the dive
7:59
within about 10 or 15 meters of the shot
8:01
line, which is part of my kind of risk
8:04
reduction strategy. So if I do need to
8:06
bail out, I know I've got an easy way of
8:08
getting home. I'm not miles away at the
8:10
far end of the wreck or anything like
8:11
that. So skipping forward a few more
8:14
minutes and my dive is now over. I'm
8:16
returning to the shot line and I'm going
8:19
to start the ascent. You can see that
8:21
the P2 is still it's still in and around
8:25
that 1.4 1.5 for the cell that is
8:28
failing. So, it's it's starting to get,
8:31
you know, carry on getting worse. But
8:33
even if that cell was the only one that
8:35
was reading correctly, 1.5 bar P2 is
8:40
still not the end of the world, it's
8:42
it's obviously, you know, not great and
8:44
I prefer it to be less. But the reality
8:47
is is that 1.5 is is kind of okay. In
8:50
fact, I know somebody who does their
8:52
entire dive on 1.5 bar. So, you know,
8:55
once again, this is about big boy
8:56
decisions. It's about risk. It's about
8:59
all those kind of things. And I am
9:01
personally happy or would be happy if
9:04
that was actually reading correctly and
9:06
it was 1.5 bar. But of course I'm
9:09
operating on the assumption that that is
9:11
the bad cell. The other two are okay and
9:13
therefore I am actually breathing 1.3 or
9:16
thereabouts bar P2. So skip forward
9:19
again. You can see here I've ascended
9:21
quite a bit. The next item on the
9:22
agenda, as people who have seen my other
9:24
videos will know, is that what I'm going
9:27
to do is I'm going to up the P2 to 1.5
9:30
bar to accelerate my decompression. And
9:33
I'm just in the process of doing that on
9:35
my Inspiration handset. You'll see the
9:37
P2's uh rise very shortly. And then I'm
9:40
going to do the same thing on my sheer
9:42
water. And the reason for doing that is
9:44
to accelerate my decompression. So to
9:48
obviously allow me to get out the water
9:49
quickly. And as I do that, you will see
9:52
that the P2 on the middle cell uh rises
9:54
and stays, you know, that kind of 0.1
9:57
maybe 2 bar above the uh where the
10:01
voting logic is. And I'm still getting
10:03
alarms all the time that this is
10:05
happening. But once again, I'm quite
10:08
comfortable with those. I'm happy that I
10:10
know what is happening. I'm happy that
10:13
even in the worst possible case and I'm
10:15
breathing 1.7 bar of P2, it is something
10:19
that I am I'm kind of willing to accept
10:21
the risk of. And part of the reason for
10:24
that is that I'm now on my decompression
10:25
stops. So I've reduced other risk
10:27
factors associated with P2. So I am no
10:30
longer working hard. I am shallower. My
10:33
anxiety is less and all those kind of
10:35
things. And of course for um it's normal
10:38
on open circuit to plan decompression
10:40
stops at 1.6. six bar P2. Anyway, so
10:44
even in the worst possible case, I'm not
10:46
a million miles from that. You might
10:48
say, well, why don't you just bail out?
10:50
And of course, that is completely an
10:52
option. I could I could bail out. I just
10:55
don't see at this point in time that
10:57
there's any rationale to do that. I'm
11:00
confident. I know what's happening. I'm
11:04
willing to accept that 1.7, you know,
11:06
1.8 bar P2 is okay. Now, you may have a
11:10
different view on that, and of course,
11:11
that's absolutely fine. It is increasing
11:14
the risk of an oxygen hit. There is no
11:16
doubt at all if it is 1.7 or 1.8, but as
11:20
I've already said a load of times, I
11:21
don't think it is. I'm fairly confident
11:23
I know what's happening.
11:25
This is a bit further on in the dive. As
11:28
you can see, things have changed quite a
11:30
bit. I've continued to kind of monitor
11:32
what's happened, and I've seen that
11:34
middle cell just continue to rise, the
11:37
P2 rise and rise. I've been watching the
11:39
other two sales and make sure that
11:41
they're responding appropriately so that
11:43
they're not limited. They're not they're
11:45
not staying uh static. So, I'm pretty
11:48
confident that it's the uh I've got two
11:50
good cells and one bad cell. But, you
11:53
know what? I want to absolutely confirm.
11:55
So, I'm going to do a deal flush. Now,
11:58
the very first thing is to put the set
12:01
point from high to low. And you can see
12:02
it's changed from 1.5 to 0.7. That's the
12:05
very small number in the top left hand
12:07
corner. The next thing I'm going to do
12:09
is pump dilluent through the rebreather
12:11
and I'm going to expect the cells to
12:14
fall to the ambience P2 which is at this
12:18
depth and this gas is about.3 something.
12:21
It'll only happen very briefly and then
12:24
it will rise back up to the low set
12:26
point of you can see the uh the the dill
12:28
flush is happening. You can see the uh
12:31
very briefly you can see the two oxide
12:33
cells dropped down to about.3 something.
12:36
The the middle cell basically uh didn't
12:38
do very much. And then what's going to
12:40
happen is is the cell should rise back
12:43
up to the low set point 7. And you can
12:46
see that's happened. And you can see the
12:47
the middle cell has just behaved really
12:50
really badly. So it's gone straight up
12:51
to 2.55 again. Now, if there was 2.55
12:57
P2 within the rebreather, my solenoid
13:00
would have need to been firing an awful
13:02
lot to get enough oxygen in it. I've
13:05
been having to vent gas from the loop
13:06
and all sorts of things. So, it's clear
13:08
to me that that that you the 2.55 is not
13:14
What you'd normally do in this situation
13:16
is put the set point back up to high set
13:18
point. I'm not going to do that though
13:20
cuz I want to get some uh a bit of video
13:22
footage to share with you guys. And you
13:24
can see there I'm using my dive vulk
13:26
just to record what I'm seeing from my
13:30
And there you go. You can see it really
13:32
clear. I've done the deal flush. I've
13:34
got two good cells. One cell's
13:36
completely failed. And therefore the
13:38
question is what now? What I do is I
13:41
pump the P2 back up to 1.5. I know that
13:44
I've only got two good cells and I do
13:46
the rest of the dive on two good cells,
13:50
staying on my unit, just keeping an eye
13:52
on them. Clear my decompression, get out
13:55
the water. Jobs a gooden. So, let's
13:58
think about some takeaways then. The
14:00
first thing, of course, is to check your
14:02
cells are working at different points.
14:05
The first one is clearly a calibration
14:07
before you get in the water. Second
14:09
thing that's also important is a
14:11
linearity check or at least something
14:13
that confirms that the cells are working
14:15
at the bottom of the dive and are able
14:17
to operate within the limit that you
14:19
expect for the dive. And you'll have
14:21
seen that happened when I got the oxygen
14:24
spike, I guess, on the descent. And the
14:26
next thing is understand what is
14:29
happening with your cells. And I think
14:32
I've explained through this dive that I
14:34
was on top of them. I understood what
14:35
was going on. and then consider what the
14:38
worst case of what you might be seeing
14:40
is. So for me, a 1.5 P2, 1.6, 1.7, even,
14:45
you know, 1.8, it it's not great. It
14:47
does increase the risk, but there are
14:49
ways to mitigate this. And of course, I
14:51
never thought it was correct, and I
14:53
think I had fairly good evidence for
14:54
that. The other thing that is really
14:56
important is a dilluent flush, which
14:59
provides confirmation of exactly what
15:01
was going on. And you saw me do that
15:03
when the P2 or at least the potential P2
15:07
because I never thought it was the
15:08
actual P2 rose above a level that I
15:11
considered acceptable. Now, I'm sure
15:13
that plenty of people are already uh
15:16
typing away in the comments section. I
15:18
look forward to uh your thoughts. I'm
15:20
sure people will have different views on
15:22
what I should have done. And you know
15:24
what? That's absolutely fine. I welcome
15:25
it. At the end of the day, those are
15:27
your decisions. These were mine. And
15:30
that I think is uh the context in which
15:33
it should be discussed. And you know
15:34
what? I'm really happy with my
15:36
decision-m on this dive.
15:38
So some sometimes you kiss a few frogs
15:41
and today was a frog kissing day.
15:45
uh this was absolutely beautiful till
15:47
about 50 m and then it it got got pretty
15:52
rubbish. You dropped down and as soon as
15:53
we got on the wreck, you could see big
15:54
blocks of coal everywhere. So, I knew
15:57
that this wasn't the tamper. And then uh
16:01
went along the remains of it a bit,
16:03
found a couple of boilers,
16:07
uh which is obviously wrong cuz Tab's
16:09
only got one boiler. Then found a
16:11
twocylinder compound or two-cylinder
16:13
engine. So, it's an old it's an old
16:16
Collier. And yeah, that was about it.
16:19
Other than that, I had a self failure.
16:20
So, all my cells completely died. Um,
16:23
which is quite exciting. But yeah, there
16:27
we go. Another frog. There's always
16:32
For anyone interested in what happened
16:33
to the cell, well, there's only one
16:35
thing you can do with uh an oxygen cell
16:37
that's let you down underwater. That's
16:39
say thank you very much for the service
16:41
that you provided. But your time is now
16:43
done. If you enjoyed this video and you
16:46
want to see other videos where stuff has
16:48
happened underwater, you may be
16:50
interested in my bailout video after my
16:52
rebreather flooded. I've also got
16:54
another one where my handsets flooded
16:56
underwater and there's also the famous
16:59
one where my scooter went rogue and I
17:01
had to ditch it. So, loads of
17:03
interesting videos there. It would also
17:06
be great if you could do all the usual
17:07
YouTube stuff. So, give us a like, uh,
17:10
drop us a comment, subscribe, turn on
17:13
notifications, but of course, mainly
17:15
what I'd like you to do is watch another
17:16
one of my videos. So, thank you very
17:18
much for listening and watching.
