DIVE report into alternative air sources
all used one in training, we all know why we carry them, but are
we really prepared to use our alternative air source in an emergency?
And if we do, will it actually work?
Running out of air is
one of the primary causes of diving incidents and deaths. Out-of-air
emergencies happen, regulators do fail, and there's no reason it
won't happen to you. All divers need to be able to choose the right
back-up system for their type of diving and they need to practise
DIVE carried out a series
of tests with a large group of divers in Gibraltar - some were relatively
inexperienced, many were highly-qualified instructors. The results
revealed that great care is needed in picking the right alternative
air source and far, far more practice is necessary for using one.
You're nearing the end
of your dive and suddenly your buddy swims up to you, arms flailing
and eyes like saucers. He's out of air and you have to deal with
it. If you're recently trained, or practise regularly, there may
be no problems - but how many divers regularly practise safety exercises?
If your response isn't immediate, you can be sure the situation
will get worse.
We video-taped two days'
footage of ten buddy pairs simulating an out-of-air emergency. On
day one divers were paired with familiar buddies, on day two we
mixed them up, and in most cases we paired people from different
training backgrounds. They were asked not to discuss the exercise
before the dive, but just to get into the water and carry out the
simulated emergency. The results help to build a clear picture of
the problems that can all too easily be encountered.
Confusion over signals:
The absence of a standard signal led to a communication breakdown.
The BSAC divers indicated 'out-of-air' with a chopping action to
the throat. The PADI divers did it by drawing their hand across
the throat - this was interpreted as a danger signal by the BSAC
Alarmingly, we observed inadequate signals from almost half the
divers taking part in the tests. Only 40 per cent used an exaggerated
motion that would have been easy to interpret in low visibility.
Most of the divers
delayed their ascent unnecessarily: As soon as two divers are
breathing from one cylinder they must begin their ascent immediately.
We expected to see a fairly straightforward ascent to the surface
from our test divers. What we actually saw was nothing like that
- 50 per cent of the pairs delayed their ascent for an unnecessary
period of time. In two cases no ascent was made for more than two
minutes - a serious waste of air.
Most of the divers
failed to form a good grip: It's vital that both divers get
a secure grip of each other as quickly as possible. If they separate,
the out-of-air diver will lose his or her only air source and may
drown. Only three pairs carried this out successfully. Most of the
divers, including some highly-qualified instructors, appeared unsure
of which grip they preferred to use and even which hand to hold
on with. We watched divers completely releasing their grip to dump
air from their BCD or drysuit.
Some of the divers descended without noticing:
The exercises were carried out in mid-water. Of the ten pairs, three
descended several metres and seemed unaware of it. Incident reports
detail divers accidentally descending 25m to the sea-bed before
Practice makes perfect: Only 26 per cent
of the test divers regularly practised alternative air source ascents
- it showed. There was a significant improvement in most of the
divers' performance on the second day. They seemed far more confident
when carrying out the ascent, despite the fact that they were now
diving with a completely unfamiliar buddy
signals for 'I am out of air' would ideally be identical regardless
of the training agency. Unfortunately, as the diagrams show,
this is not the case.
Know what it feels like
to be running low on air. If you've experienced the sensation
of your air running out once, you probably won't forget it.
To safely simulate running out of air you should be in a shallow,
controlled environment, such as a pool. Have your buddy turn
off your air while you watch your gauge. When you can't get
any more air from the regulator, signal out-of-air, and your
buddy can open the cylinder valve again.
If you're out of air,
use the signal you know. Make it clear, and don't stop signalling
until someone responds. If you get no response, take your buddy's
alternative air source.
Always grip your partner
with the right hand. This will make it easy to dump air from
your drysuit or BCD without needing to release your hold. Taking
hold of your buddy's BCD shoulder strap is taught by many instuctors,
but is it really the best grip? What happens if the diver has
a stab jacket with no shoulder straps? The forearm-to-forearm
grip is better. If you're the one giving the air, the physical
contact will reassure the out-of-air diver you're not going
to let go and you'll feel their grip get tighter if they begin
Don't hang around. The
more breaths you each take before beginning the ascent, the
less likely you are to be successful. Make the minimum of signals
and head for the surface. There's nothing wrong with using a
quick squirt of air to get you both moving. Gauges can be checked
once you're on your way up - they will confirm you are ascending.
- If you're at depth, make the first part
of the ascent quickly and slow down as you reach the last 10 or
15m. You don't need to ascend at the speed your computer indicates
you should, as it's probably a lot more conservative than you
can afford to be at this stage.
- If you're the receiver of air, let your
buddy take control of the ascent. He or she is the one with the
air. If you're the air donor, take charge of the situation. This
will reassure the other diver and should reduce the chances of
- Practise as often as you can, it does make
a difference. We suggest practising an ascent from time to time
at the end of a normal dive - if you do, make sure you have discussed
it with your buddy prior to your dive and that the conditions
- Include the out-of-air emergency in all
pre-dive briefs. Discussing signals and procedures before entering
the water will leave you in no doubt of the correct action to
take. Remember, your time on the surface isn't limited, but underwater
you'll value every second.
It's important to choose the appropriate type of alternative
air source for the diving you do. Divers usually use one type
in training and often look no further when choosing their own
alternative air source. If they become involved in more adventurous
diving they run the risk of being poorly equipped to deal with
an emergency. We took different types and makes of alternative
air sources to the BSAC maximum recreational depth of 50m. Performances
were monitored at low tank-pressures and during ascent.
All the equipment used was new or well-serviced - that way we
could be certain that any shortcomings were not due to poor
maintenance. Where possible the alternative air sources were
used on a balanced and unbalanced first stage to observe any
change in performance. We used different makes of the same type
of alternative air sources to gain more accurate results. We
have not compared one make to another, and it must be remembered
that testing was subjective.
The octopus is the most commonly-used alternative air source.
This is basically any regulator second stage intended for use
as an octopus, although most divers use a manufacturer's dedicated
octopus second stage, which is brightly coloured and connected
to a longer hose. Choosing the same make of octopus as the first
stage and primary second stage ensures the best performance.
Divers who make penetrations into wrecks or caves must use an
extra-long, two-metre hose to enable a buddy to breathe from
the alternative air source while swimming directly behind them.
These have been adopted by other recreational divers who prefer
the system. Of the alternative air sources we tested, the octopus
system provided the highest performance. We would recommend
you use the highest performance first stage you can afford.
The performance of your octopus is directly affected by the
ability of the first stage to deliver enough air - this becomes
very important when there are two divers breathing from one
regulator. The octopus is a safe system to use at depth, but
you must carry enough air in reserve for two divers; or use
a pony cylinder.
These combine the octopus with the inflator of a BCD, either
integrated into one unit, or as a specially-designed octopus
placed in line with the inflator. Its location dictates that
in an emergency, the air donor must offer their primary regulator
to the out-of-air diver, using the octo-inflator themselves.
Photographers' models choose to use them to reduce the number
of hoses that show in a picture, or travellers, who wish to
carry the minimum amount of kit. We were surprised by the relatively
good performance of these at 50m. There was more breathing resistance
than with the octopus regulators during both inhalation and
exhalation, but they delivered good amounts of air. Their effectiveness
in a real emergency is something that can't be tested. We recommend
this system is used at shallower depths and with a buddy who
is familiar with it. If you do use an octo-inflator, remember
that dumping air through your inflator might be a problem when
you're breathing from it (some new systems have overcome this
problem). Fit an independent pull-dump on the opposite shoulder.
Redundant air is the choice of most deep divers and other more
conscientious divers. While small redundant air supplies with
built-in regulators do exist, they provide little air. To be
of any real use in an emergency, you need a two- or three-litre
pony with a first and second stage regulator. Divers undertaking
extended decompression stops will carry larger redundant air
or Nitrox, should it be required. With a pony set-up there should
only ever be one diver breathing from it, which creates less
demand on the first stage. So, if you can't afford a high performance
regulator, go for a basic but robust system for use with a pony
bottle. Remember, if you ever find yourself using it there's
only one way you should be going - up!
- For normal recreational diving, consider
a pony cylinder. It's the safest way to dive. It provides
you with a completely redundant air supply that can be used
in any emergency.
- It's probably best to use a three-litre
pony. Some manufacturers offer two-litre cylinders. They
are more compact, but the bottom line is that you have less
- Never plan to use your pony for air
during any dive. It should be regarded as a bail-out system
only; not as an ascent cylinder. Misuse has cost lives.
- If you're planning a decompression
dive, a three-litre pony may not provide you with enough
air to safely complete decompression before ascending. Consider
a larger redundant air source, or at the very least, a safety
cylinder hung at your stop depth.
Breathing rates vary dramatically between divers, a fact that
must be taken into account when determining the correct amount
of air to leave in reserve on a dive. You may think you've allowed
enough, but what happens when your air-guzzling buddy wants
some of yours as well? We ran some tests on air consumption,
and got some revealing results. Dives were made in pairs, following
the same profile, with a maximum depth of 50m - two sets of
stops on ascent, one minute at 9m followed by six minutes at
6m. Total ascent time was 11 minutes. The test air was carried
in redundant cylinders. The divers only switched to the test
air as they began ascending.
One pair used more than half their
air during the ascent: On reaching the surface one pair
had breathed 1,300 litres of air. The second pair had used
1,000 litres. If this had been a real dive and the agreed
air reserve pressure was 100 bar (a realistic pressure), the
first pair would have run out during ascent - forcing them
to omit mandatory decompression stops.
A full three-litre pony bottle didn't get one diver to
the surface: Before ascending, the diver switched to the
full pony bottle. After just five minutes the cylinder was
at 100 bar. Two minutes into the 6m-decompression-stop it
ran out. In just two breaths the regulator went from 'breathing
fine' to failing to deliver air - an indication that failure
to check your cylinder pressure could be fatal.
The pressure inside the pony bottle dropped significantly
as it cooled at depth: The cylinder had been filled at
least two days before it was used on the dive. At the surface
it read 200 bar, but at 50m the pressure was only 170 bar.
.24 per cent of the test divers were entry level
.41 per cent of the divers had taken training beyond entry level
.35 per cent of the divers were instructors
.40-50 per cent had used an alternate air source for real.
Calculate your ascent gas
Litres per minute breathed on the surface x full ascent time
x absolute pressure in bar at start of ascent = litres of
gas required for the ascent
Litres of gas required x 1.5 = reserve
The widely-used practice of finishing a dive with 50 bar is
rarely questioned as a safe diving technique. If you undertake
deeper decompression dives with mandatory stops, consider a
far larger reserve. Some cave divers estimate that it may take
as much as five times the amount of air to support two divers
in an emergency as one breathing normally. Technical divers
calculate the amount of air they need for a dive and then double
it as a safety measure. For most recreational decompression
dives you don't have to go quite that far - a further 50 per
cent in reserve should suffice. The equation on the right shows
how to calculate the amount of gas you will need.
can go wrong
Blind reliance on an alternative air source may be misplaced
and could cost your life and that of your buddy. There are many
reasons why a diver may not be able to breathe underwater. These
can be loosely categorised into problems of technique which
reflect an individual's personal skills and training, and equipment
failures for which the diver may or may not be wholly responsible.
These examples either reflect incidents we have personally witnessed
or are drawn from documented accident and fatality reports.
- Myth and Reality
While the buddy system has been the cornerstone
of safe diving as defined by the training agencies, the concept
is now under re-evaluation. Several agencies including the
BSAC are believed to be considering making solo diving legitimate
in some circumstances. Incident reports indicate that in many
situations the buddy diving system has not saved lives. During
shared ascents that appear to have been progressing well,
the sharer has suddenly rejected the mouthpiece and inexplicably
broken away. If panic is to blame then agencies need to establish
why divers panic and what measures can be taken to prevent
it. Using an independent air source means the minimum of task
loading - simply switch regulators and make a normal ascent.
Buddy dependence and the task loading encountered in an out-of-air
scenario may be too much for some divers.
- Out of air - You would be amazed at
the number of people who think an octopus will miraculously
provide them with air despite their tank being empty. Alternative
air sources connected to your tank obviously DO NOT work
when that tank is empty.
- Free-flows and lock-ups - A free-flow
can leave you totally out of air unless you have another
cylinder. A first stage lock-up will cut off the air supply
to both primary and secondary mouthpieces.
- Inadequate performance - Air sharing
will at least double the demand on your regulator. A low
performance, poorly-maintained first stage may fail to deliver.
- Breathing from wrong gas source - Divers
using ponies have been known to accidentally begin the dive
breathing from their pony regulator. When the pony ran out
at depth they spat out the mouthpiece, believing their primary
had failed, and reinstalled the regulator from the empty
pony with tragic results.
- Inadequate gas supplies - An AAS is
only good for as long as it lasts. If there is insufficient
gas in it to get you, or you and your buddy, to the surface,
it's nearly useless. You'll simply run out again.
- Inaccessible AAS - We've seen AASs
zipped into BCD pockets and secured to D-rings with karabiners.
Seconds count. Failure to quickly and cleanly deploy or
obtain an AAS may render it useless in an emergency.
- Poorly maintained secondary - We've
seen one second stage with a paper clip in it, know of another
that was home to a fireworm, and have breathed off regulators
with leaky exhaust valves or diaphragms. Some we've tried
have been almost impossible to draw air through, even in
- Deliberately disabled secondary - One
tester had disconnected his combined octopus/inflator hose
because a valve failure meant it kept inflating his BCD.
- Problems with pressure gauge readings
- Over time, many gauges lose accuracy. Fatalities have
occurred, for example, when the pressure gauge read 40 bar
but the tank was empty. In other incidents problems have
occurred with air remaining. It's possible that while air
remains in the tank the regulator can't supply a sufficient
volume to support both divers.
- Air turned off by accident underwater
- Incidents have occurred when cylinder valves closed as
they became caught on cave walls or wreckage. In cases where
divers have used more than one cylinder, the wrong valve
has been turned off by accident, leaving a diver without
- Unfamiiar kit - Purge buttons are
not always obvious and second stages can seem to face the
'wrong' way. This can increase the chances of the second
stage flooding, or breaking your mask seal with the upturned
exhaust tee. Anti-free-flow devices also make breathing
more difficult and may cause additional stress. Task loading
can become insurmountable.
Small-volume air cylinders with in-built
regulators are available as last ditch attempt safety devices.
They are not a substitute for an alternative air source, as
they only contain around 80 litres (a pony bottle, by comparision,
usually holds 460 to 700 litres). Our limited testing did
not establish a maximum operating depth from which these alternative
air sources would bring a diver to the surface. Although claims
of up to 48 breaths on the surface are made, we found our
testers got between 17 and 32. An ascent begun at 40m emptied
the cylinder by the time 30m was reached. It provided just
five breaths. However, we were surprised at how well the unit
breathed at depth.
1. HOSE UNDER THE RIGHT ARM
At a recreational diving level, equipment configuration is
discussed but never really highlighted as an important element
of safe diving. For this reason it's something many divers
never truly understand. If we're lucky, we may learn some
basic tips, such ensuring the octopus is the last hose to
be attached, so it is unobstructed should it need to be released
quickly. This is an attitude far removed from that of the
technical diving community, for whom configuration is emphasised
as a critical safety element. In fact it is recognised as
an area that demands hours and hours of fine-tuning in the
water and on the surface.
Here are some basic ways of wearing an
alternative air source. Find a method
you are comfortable with and stick to it - and make sure you
know how your buddy configures his or her alternative air
This is the most conventional way to carry an alternative air
source. FOR: The
hose is kept under the arm, reducing the chances of it snagging.
AGAINST: The diver must
release it from under their arm when it's being used. It's difficut
for an out-of-air diver to locate the second stage unless their
buddy is facing them.
RECOMMENDATION: This system
must be used with a coloured hose.
Hose under the left arm - This system is the same as
under the right, but any diver who uses it must have the correct
second stage. A dedicated left-hand regulator or one designed
to be used from either side must be used.
2. HOSE OVER THE SHOULDER
||This has been adopted by some
recreational diving instructors.
FOR: The hose is unrestricted.
If a diver needs to use the alternative air source, they simply
take it. when it's used with a coloured hose it is clearly visible
to other divers.
AGAINST: The hose is more likely
to become snagged.
3. SECOND STAGE POSITION
||There are various views on
the most appropriate place to secure an octopus second stage.
The 'torso triangle' is taught by training agencies and serves
as a rough guide for novices. Some would argue that the bottom
right position is best for right-handed divers, and the reverse
for left-handers. We found it was most visible towards the top
half of the chest.
The extra-long hose came from cave divers, who sometimes need
to exit small spaces, so can't dive side-by-side.
The additional length is more comfortable for the diver breathing
from the alternative air source.
AGAINST: It's easy for
divers to drift apart, as the out-of-air diver would feel
less likely to lose the second stage.
This system is an excellent choice for divers involved in
any advanced penetration diving, but the extra length of hose
must be stowed correctly. For these set-ups, your primary
regulator is your octopus.
Set-up 1: For this system, simply
tuck the excess length of hose into bungees around your cylinder.
If you donate the octopus, the hose will come loose as your
buddy pulls it.
Set-up 2: Only for experienced
divers. Bring the second stage on the long hose under your
right arm. Take it around the back of your neck and stick
it in your mouth. If your buddy needs it, they take it out
of your mouth and you dip your head to help its release. You
then breathe from your other second stage.
Here is a selection of some of the most popular models of alternative
air source available in the UK.
. This article required a massive co-operative
effort from all sectors of the Gibraltar diving community. We should
like to thank all three of Gibraltar's dive centres for their support
- Rock Marine, Dive Charters and SM Henshaw Dive Hire. We are grateful
to the members of the three BSAC branches who contributed - Noah's,
the Gibraltar Sub-Aqua Club and 317 Special Military branch. We
would also like to thank divers from the Gibraltar Police, Gibraltar
Customs and the Gibraltar Regiment. We would finally like to acknowledge
our liaison officer Captain Danny Freyone of the Gibraltar Regiment.