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Scuba Professional: Column No. 4



“How Did That Get in There?”

Simon Pridmore looks at the common practice of filling scuba cylinders while they are standing in water and asks “Why?”

Anna is a new diver.

“I was on my ninth dive ever, about five minutes in and at a depth of around 12m when I realized that my air was not coming out smoothly. I couldn’t think why this should be. I had checked my pressure gauge on descent and it had shown 190 Bar. I switched to my octopus, but there was no difference. Soon the air became very thin.

I tried to stay calm. Everyone else was going deeper and swimming away from me. Then the air stopped completely. I held my breath. I looked around and there was my husband. He gave me his regulator and took me to the surface with him.”

Anna’s husband, an experienced instructor, takes up the story.

“I had checked my wife’s set up as usual before the dive. The pressure gauge was showing 190 Bar on the surface. A few minutes into the dive, I saw her hovering away from the reef in mid water, sensed something was wrong and swam towards her. She gave me a wide-eyed look and pointed at her regulator. I glanced at her gauge and saw it was at zero so I gave her my octopus and we went up together. “

“I was puzzled as to how a full tank could become empty so quickly. We were definitely no more than 10 minutes into the dive and there had been no O-ring blow out. After the dive, I removed the regulator and opened the tank valve. Nothing came out. Some instinct made me turn the tank upside down and, to everyone’s surprise, water started flowing out of the valve. It was fresh water!”

An Incredible Story?

Standard aluminium scuba cylindersIt seems incredible that a scuba cylinder should be so full of water that a diver would only get a few minutes of air. Some might interpret the story simply as a misunderstanding on the part of a new diver with a supportive husband.

However, when I heard the story, it brought to mind something that I came across when I had a dive store in Guam. We used to conduct annual visual inspections on cylinders owned by local residents and were surprised to often find a few centimetres of water in the bottom of cylinders. This was always fresh water, not seawater. We made some enquiries and found that this is fairly common and comes from the almost universal practice in dive stores around the world of filling scuba cylinders while they are standing in a trough of water.

The fill whips, hoses that are clamped onto the valves of scuba cylinders to fill them, sometimes drop into the water trough between cylinder fills. When the wet clamps are then attached to the valve of the next cylinder and the airflow is turned on, the pressure of the air in the fill whip is higher than the pressure of the air in the cylinder and water droplets are driven into the cylinder.

Fill the cylinder several times and the amount of water inside accumulates until you have a little pool in the bottom. The moisture inside causes corrosion to build inside the cylinder too.

Bear in mind that I was in Guam, part of the USA, where a stringent system of cylinder inspections applies and is enforced by dive operators. The maximum length of time between inspections is 12 months so that means the water inside the cylinders had accumulated in less than a year.

In many places in the world where people dive, including the island nation where Anna’s dive took place, there are no regulations governing cylinder inspection, so it is possible that a cylinder could go for many years without anyone examining the interior.

Therefore, Anna’s story is not as far-fetched as it might initially seem. With her cylinder containing a large amount of fresh water, the volume of air in the cylinder was quite small so once she started her dive she used it up very quickly. The reading on her pressure gauge must have been dropping fast during those first few minutes of her dive but she did not notice.

Why Do They Do It?

Dive centres fill cylinders while they are standing in water for three reasons:

  1. To keep them cooler during the filling process, which generates heat, so they can fill them faster and so the air pressure inside does not drop so much when they cool down afterwards and they don’t have spend time hooking them up again to top them off.
  2. As a convenient way to wash salt off them post dive, and
  3. To protect the filler from harm if the cylinder explodes during filling.

All three of these reasons are the product of fuzzy thinking.

  1. Filling the cylinder in water has very little impact on the cylinder temperature, partly because the heat from the filling process is transferred to the water, which then gets warmer. Fast filling still causes the cylinder to get hot, despite the water bath, so it still has to be filled to 20 Bar or so beyond its rated pressure. This makes sure that the pressure is 200 Bar or more when the cylinder is cool. Otherwise divers will complain. The only effective way to stop a cylinder getting too hot while it is being filled is to fill it slowly and from a bank of large cool high-pressure air cylinders rather than directly from the compressor.
  2. Using the fill bucket to wash the salt off the cylinder is ineffective as all that happens is that the water the cylinder stands in becomes a little salty. A quick fresh water blast with a hose before the cylinder is taken into the compressor room does a much better job.
  3. Aluminium cylinders have exploded during the filling process in the past and when this has happened the consequences have often been fatal. However, an exploding cylinder is a bomb and no concrete trough is going to protect the person filling it. Instead it will just contribute more shrapnel to the explosion.

Having said this, those aluminium cylinders that exploded were made from a 6351 alloy containing lead and it was the presence of lead in the alloy that created the problems that caused them to explode. Since 1988, no aluminium scuba cylinders have been made using this alloy or with any alloy containing lead. The vast majority of scuba cylinders in service today worldwide, including all cylinders made by Luxfer and Catalina, the top two manufacturers, are made from an alloy called 6061.

Although, during annual inspections, cracks have occasionally been found in 6061 cylinders, none has exploded: ever! And there are millions out there.

No Need for a Bath?

It is worth noting here that not all dive centres that fill cylinders in water are ignorant and negligent. There are many dive centres that fully recognise the potential issues and take elaborate precautions to make sure their whips and cylinder valves stay completely dry during the filling process so that water does not get into their cylinders.

But if,

  1. The likelihood that a scuba cylinder will explode during filling is so remote,
  2. A water trough will not protect a filler if it does happen,
  3. The water trough is not an effective way of removing salt or reducing the cylinder’s temperature sufficiently and,
  4. The practice of wet-filling can allow water to enter a cylinder and lead to an incident such as Anna’s,

why do it at all?

Ironic, isn’t it, that, from day one, divers are constantly told always to leave some air in their cylinder at the end of a dive so that no water can get in! And yet ……

Read more from Simon in his latest release Scuba Professional – Insights into Sport Diver Training & Operations and his bestselling book Scuba Confidential – An Insider’s Guide to Becoming a Better Diver, both available from Amazon in paperback and e-book versions.

Simon Pridmore is the author of scuba diving books, travel books and, as you might expect, scuba diving travel books. Originally from the UK, Simon has lived in Asia for over 30 years. As well as his books and guides, Simon writes regular columns for a number of magazines. He and his wife Sofie currently live in Bali, Indonesia but spend a lot of time exploring other places trying (but failing so far) to find a cure for their itchy feet. Simon's latest book - Scuba Exceptional – Become the Best Diver You Can Be - the follow-up to his best-selling Scuba Confidential, is available now in paperback and e-book versions from Amazon stores worldwide. Find out more about Simon and his books on

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Deptherapy returns to its Roots – Part 7



Join Richard Cullen from Deptherapy for the final part of his Blog about the charity’s recent expedition to Roots Red Sea, El Quseir, Egypt.

Deptherapy expeditions do not just magically happen, they need planning and they need funding.  This expedition was funded by our long-term partners the Veterans’ Foundation.  The funding is part of a grant they awarded us for programmes this year, which were then put on hold because of COVID.

All charities in the Armed Forces’ Sector are struggling for funds. Deptherapy desperately needs support going forward and every penny counts.

We know what we do works and at the end of this blog you will find details of the research studies into Deptherapy’s programmes and how they impact on the lives of our beneficiaries.  This includes details that are hot off the press about the latest study that reports that what we offer through scuba diving and 24/7 support has benefits beyond those found in other sporting rehabilitation programmes.

Well tomorrow we fly home, late in the evening with the journey home for some of the guys who live up North taking around 15 hours after leaving Roots.

We want to make the most of today but with the tide running we are not going to be able to dive until later this morning which means only two dives today.

Oatsie and Swars about to start their sidemount dives

Things, however are really busy over at the dive centre with Swars and Oatsie putting their sidemount kit together for their training dives with Steve Rattle leading to their RAID sidemount qualification.  It has been nice to be able to offer the guys this extra training, given the amount of work they have put in this week.  They have needed to get through their theory quickly but given the RADI online learning system this has not been too arduous.

Steve came diving with us yesterday to get some more photos and was really amazed at the progress that Corey had made. He was quite open in his praise, as in his view Corey has gone from a non-diver to being a very competent OW diver capable of diving, unsupervised, with a buddy.  Praise indeed.

Other than the sidemount course we are diving as a group today: Corey, Keiron, Michael, Moudi and me. Corey has been given some tasks – SMB deployment on both dives and the afternoon dive will be a ‘naturalist dive’.  Guy Henderson has set Corey a task: ‘to identify three species of fish and record the time into the dive and the depth at which each one was spotted’.  Guy runs Marine Biology courses on the reef and knows where the fish are to be found, how long into the dive, and at what time.

The two Toms are getting put through their paces. They have walked their cylinders down to the entry point, but Steve sends them back to the dive centre to collect other kit they should have brought with them.

Our general dive goes well and the sidemount guys appear from their sidemount dive some 90 minutes after dipping their heads under the water.

Corey enjoying being a RAID OW20 Diver

Lots of bubbly chat at lunchtime, a group of really happy divers. Corey really has benefited from the week and over lunch thanked the team for making him a diver. He has very quickly become part of the family and after returning home he published an amazing post on Facebook about his experience.  Corey really gets Deptherapy and had soon realised that we see past mental and physical injuries and see the person inside and work with that person.  He also realised that we want beneficiaries to see their fellow beneficiaries in the same light.  He knows he now has another ‘family’ – a family of brothers in arms who have two things in common, they served their country and they have suffered life changing injuries or illnesses.

Back into the water for the afternoon dive and Corey identifies the fish and records the details on a slate.  The two Tom’s complete their second dive and qualify as RAID Sidemount Divers. Great!

Kit packed away and it is time to return to the camp for a few well-earned last night drinks.

I am often asked why we use Roots as our exclusive base for diving. I have mentioned before that it offers us an ideal retreat, away from the hustle and bustle of everyday life. We are secluded and there are no distractions such as late-night bars etc.

Roots Accessible Room

The second reason is the amazing welcome we receive from Steve, Clare, Moudi and the team.  We have been going to Roots since 2014 and many of the staff have become good friends, they understand our needs and are the friendliest people you could ever wish to meet.

The third reason is the huge investment Steve and Clare have made in making the resort and dive centre accessible for those with physical injuries including those who need to use wheelchairs.  All our beneficiaries can enjoy Roots and, in fact, love it here.  The reef is perfect for us and in non-COVID times we can travel to the Salem Express and other dive sites to enjoy more of the Red Sea experience.

Accessible toilet on the Roots beach

After discussions with the team I was very proud to be able to tell Corey that his progress had been such that we were inviting him on the Armed Forces Covenant Fund Trust sponsored two-week Marine Biology Course at Roots in June 2021. There is lots of homework to undertake under the guidance of Dr Debbie McNeill of Open Oceans and Corey will be sent the Red Sea Guide which is the basis for study.

While on that programme, Corey with fellow beneficiary Dale Mallin, will complete his RAID Advanced 35 course.  This all builds to a 10-day Red Sea liveaboard in 2022, onboard Roots’ new boat Big Blue where 18 beneficiaries will compare the coral and aquatic life on the wrecks of the SS Thistlegorm and the less known SS Turkia that is to be found in the Gulf of Suez and is rarely dived.

Paul Rose, our Vice President, is supporting the programme and is seeking the support of the UN and the Royal Geographical Society. A comprehensive report will be submitted to our partners in the project and to the Egyptian Authorities.

Last night and chill

What we do works:

In recent years there have been three academic studies into our work:

2018 – A study by a team from the University of Sheffield Medical School.

2019 – A study by The Centre of Trauma at Nottingham University.

Both these studies reported very positively on Deptherapy’s work both underwater but also in terms of the provision of 24/7 support.

The following is from our press release which was issued on 26th October:

‘A new study into Scuba Diving Rehabilitation Charity Deptherapy’s approach to supporting Armed Forces veterans with psychological injuries such as Post-traumatic Stress Disorder (PTSD) through the medium of scuba diving has been carried out by Petra Walker in conjunction with Hanna Kampman of the Posttraumatic Growth Research Unit at the University of East London.

This study, which used Interpretive Phenomenological Analysis (IPA), demonstrates that scuba diving has rehabilitation benefits beyond those found in other forms of sporting rehabilitation exercise. IPA is a qualitative methodology that examines the experiences of participants and has been used in previous studies of Posttraumatic Growth (PTG) in para-athletes.

Petra is an experienced diver herself and was exploring the wellbeing aspects of scuba diving as part of her Masters in Applied Positive Psychology and Coaching Psychology when she came across a previous study on Deptherapy. Past studies have mainly focused on the medical aspects of diving, so the opportunity to examine the mental health side of rehabilitative scuba diving was impossible to ignore. The full study is currently embargoed until it is published at a future date in an academic journal, but it follows similar academic research into the work of Deptherapy by the University of Sheffield Medical School (2018) and the University of Nottingham (2019).’

This is amazing news and sets us apart from other sporting rehabilitation programmes.

We are currently working with our VP Richard Castle who is a Consultant Psychologist and our Dive Medicine Advisor Mark Downs to identify further areas of psychological and physical dive related research.

We end the week on a happy note.  A young man who has learned to dive properly with a RAID OW 20 certification, a new RAID Master Rescue Diver, two new RAID Sidemount Divers, 5 new RAID O2 Providers, many assessments for our DMs but most of all a week of learning, of making new friendships, renewing old friendships, and building on our family ethos.

Until we meet again…

For us, Deptherapy is a journey, a journey that continues to push boundaries in the use of scuba diving in the rehabilitation of those suffering life changing mental and/or physical challenges.  On our journey we want to change the way the scuba diving industry views diving for those with disabilities.

In the new year, we will be launching, with our diver training agency partners RAID, a new and exciting adaptive teaching programme that will offer diving to the disabled community. We can’t wait to share it with you!

Find out more about the work of Deptherapy and Deptherapy Education at

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Deptherapy returns to its Roots – Part 6



Join Richard Cullen from Deptherapy for part 6 of his Blog about the charity’s recent expedition to Roots Red Sea, El Quseir, Egypt.

Thursday has dawned and it is down to the House Reef with an outgoing tide that is approaching slack so we can get in the water straight away.   Lots of chat about last night’s RAID O2 Provider session with Moudi.  Oatsie is talking about sidemounts and marine biology, Swars is looking forward to his first sidemount session this afternoon.

Moudi is supported by Oatsie this morning and doing some more skill work with Keiron.

Moudi running the guys through the RAID O2 Administrator Course

Corey was asking last night about what it is like at 30 metres, so I have decided that with Michael and Swars we will take him to 30 metres.  We are going to run a narcosis exercise so out comes the slate with the numbers 1 – 25 randomly placed in squares.  Corey’s task, in the dive centre, is as quickly as possible to touch each number in sequence.  He does it pretty quickly and Michael briefs him that he will need to do the same exercise at 30 metres.

Michael briefs the dive and we set off down the beach.  Corey has improved beyond measure and he is becoming a pleasure to dive with.  So we are off to follow the South reef to 30 metres where we will complete the second part of the exercise.

At 30 metres Michael hands Corey the slate; there is a considerable difference in the time to complete the exercise at the surface and at 30 metres.  There are lots of mitigating factors in how quickly you can identify the numbers and explaining a slower time at 30 metres than at the surface does not mean an individual is suffering from narcosis.  Identifying random numbers, if you run the exercise at the surface, several times with an individual over a number of hours can result in wide variations in the time taken to complete the exercise.

We finish the dive with Corey smiling from ear to ear and we have a discussion about depth and air consumption.  The second dive of the morning is a fun dive, then it is lunch in the beach restaurant.  After the burgers I am sure we will need to look at our weighting before the afternoon’s dive.

We will need to look at weighting after this lunch!

Corey and Keiron have got into the habit of recording their dives online using the RAID online log book which is a tremendous facility and as the instructor I can access that data.

Moudi and Keiron are going for a fun dive as are Corey, Oatsie, Michael and myself. Swars is getting kitted up for the first experience of sidemount with Guy Henderson.

Swars getting to grips with his sidemount cylinders

People often look at the relationships that exist between the dive team and our beneficiaries and try to extrapolate a similar relationship to disabled students they might have.  Our relationships are built up over a period of time, in some cases over many years.  We also provide 24/7 support and have chat groups etc on social media; we also meet up socially when we can.  It is somewhat different than a individual coming in to a dive centre and saying ‘I want to dive’. Your relationship is likely to be the same as any other student, you will teach them, they might stay with the dive centre or like many that will go on holiday to do some diving, you might never see them again.

Our main aim is to create a family atmosphere for our programme members, one where they feel secure and they are able to discuss freely with the team and fellow beneficiaries their feelings and needs.

Few dive centres are charities, and owners might want to consider costs of running a course for someone with a disability that might take more than the standard four pool sessions etc.  You may find the number of sessions and the staffing levels have to increase.  Many dive centres, because of their size and turnover are exempt from providing accessibility.  How will this affect someone who is a wheelchair user?  Can they gain access to the dive centre, the classroom, the toilet?  What are the changing facilities, can they get wheelchair access to the pool?

Lots of things to think about.

Roots’ beautiful reef

The reef is beautiful, so much aquatic life and the corals look splendid, especially the pinnacles.

A good day’s diving, Swars has really enjoyed his sidemount.

Lovely way to relax in the evening with the Roots BBQ, a fitting end to a great day.

Last day tomorrow and our final blog!

Find out more about the work of Deptherapy and Deptherapy Education at

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