Entry techniques: Backward rolls

Clare took this little video on a recent boat dive. It was meant to be an example of a perfectly executed backward roll off a rubber duck dive boat, but it turned out to be something else entirely!


The way a backward roll off a boat works is that the skipper counts down (or up – he’ll tell you what he’s going to do). On 3 (or 1), all the divers roll backwards off the boat TOGETHER. It’s very important that if you’re not ready or miss the countdown, you don’t move or roll until the skipper tells you it’s safe to do so. Otherwise you could land on top of another diver with your cylinder, which could cause very serious injury.

In the video, the diver on the right is not ready, and rolls well after the other divers. Grant tries to stop him but it’s too late. Fortunately it was an extremely calm day and the boat hadn’t drifted much, so the diver didn’t land on anyone. But on a windy day or at a location with surface current, correct backward roll technique is essential for the safety of all the divers.

Series: Shark Week featuring Mythbusters – Jaws Special (Disc 2)

Shark Week
Shark Week

Shark Week features annually on the Discovery Channel. It’s been condemned for taking a sensationalist approach to sharks and shark attacks, but Tony and I loved the Air Jaws episodes produced by our own Chris Fallows of Cape Town. This two-DVD set is season 4 of Shark Week screened in 2005 (the 30th anniversary of the release of Jaws), and features a range of programs all about sharks.

I reviewed the first disc of this special in this post. Here are brief reviews of the features on Disc 2 of the DVD set.

Mythbusters: Jaws Special

I actually hadn’t watched Mythbusters until this particular show, so I was pleasantly surprised and amused. It’s basically two grown men (one with seriously foppish fashion sense) and sundry irritating hangers-on, blowing things up, building contraptions and using large machinery for inappropriate projects. The hosts are special effects designers so they have a huge workshop with every imaginable gadget at their disposal.

In this episode, they investigate some aspects of the movie Jaws, including the incidents concerning the strength of the shark (towing a boat backwards, submerging air-filled plastic barrels for hours on end, and blasting through a shark cage and then – later – through the side of a boat). They also investigate whether sharks are deterred by punches (slightly, as our own experience attests) and what happens to a scuba cylinder when you fire a gun at it.

If you don’t want to know the results of these experiments, stop reading now.

They found that while a shark could conceivably pull three plastic barrels underwater briefly, it couldn’t hold them there. It also could not tow the boat backwards fast enough to cause waves to break over the stern. It is possible, however, for a great white shark to break a shark cage, and also to make a (small) hole in the side of a (flimsy) wooden boat.

Sharks don’t like to be punched, particularly in the soft parts (gills and eyes), but, as the Mythbusters pointed out, if you’re being munched and your fists are your only weapon, then you’re going to want to use them regardless of how effective they’ll be.

Tony’s and my primary interest was in the exploding scuba cylinder (in the movie, this is how the shark is finally vanquished). After multiple layers of safety precautions, they fire a rifle point-blank into first an empty cylinder, to see whether the bullet can penetrate 2 inches of aluminium (it can), and then into a fully charged one. The entire experiment was done inside a shipping container, with the gun remotely operated.

The results were interesting: the pressurised cylinder did not explode, but took off like a rocket as the air was released through the small hole. It whizzed about inside the shipping container, denting the walls, until the air pressure inside the cylinder was equal to the air pressure outside. We could see how a cylinder having its pillar valve knocked off while in transit could turn it into a lethal weapon. The compressed air has considerable explosive power.

Shark After Dark

One has incredibly mixed feelings watching these Shark Week specials. The narration and music are all testosterone-filled, fear-inducing and press the same buttons that Jaws the movie pushes. The resources – time, camera equipment, and so on – that gets thrown at the subject, however, is awe-inspiring and one can only hope that some of the footage obtained is of value to science.

The first half of Sharks After Dark features our homeboy Chris Fallows, of Apex Predators and Air Jaws fame. He guides a film crew as they spend time on a boat off Seal Island at night, hoping to determine how active white sharks are at night. I spent the first few minutes rolling my eyes vigorously – lots of loud and vacuous American speculation in sweeping terms with no reference to the available scientific knowledge on shark sensory organs – but the eye rolling ceased when the team actually obtained footage (and Chris Fallows some incredible still photos) of white sharks breaching after seals while it was still dark. My curiosity about the water around Seal Island was also satisfied when Fallows and a cameraman got into the shallow water (about 1.5 metres deep) around the island where the seals congregate, and dived with them for a while. Let’s just say that the water clarity confirmed one’s suspicions that all that seal poop has to go somewhere!

The second section of the program dealt with bluntnose sixgill sharks – which strongly resemble “our” broadnose sevengill cowsharks here in the Cape (and are in fact also found along the Kwazulu-Natal and West Coast of South Africa, but not in Cape waters), in Puget Sound south of Seattle in the USA. These sharks live at great depths (more than 100 metres), but come into shallower water (20 metres or less) at night, in order to feed. They are dark coloured like basking sharks or the Greenland shark, and the divers and cameraman descended into a cage at 20 metres, above a fairly featureless sandy bottom. The sharks are quite sluggish, like their sevengill cousins, but can put on a burst of speed when it is required.

The final section of the program deals with sand tiger sharks (grey nurse sharks) at the North Carolina Aquarium. These sharks resemble the ragged tooth sharks on display at the Two Ocean Aquarium in Cape Town, and this may be no coincidence. Raggies were chosen for the aquarium here because of their placid natures and “sharky” appearance, which challenges one’s preconceptions of sharks when viewing them swimming calmly around their tank. The aquarists feed the sand tigers at night, in order to see whether they will eat at night (they will), and then the camera crew climb into the tank with lights on, and then with the lights off. The sharks’ behaviour was the same.

A sunken coastguard cutter serves as home to sand tiger sharks in the open ocean off North Carolina (what beautiful visibility!) and the team visits the wreck, which lies at about 30 metres’ depth, to see the sharks in the wild. Noticeably more twitchy than the sharks in the aquarium setting, the sharks come close (and closer at night) but turn on a dime and swim away very fast when they’ve come close enough. It is during a night dive on the wreck that the divers observe the sand tigers feeding.

During the preceding few sections the narrator goes a bit quiet and one can forget the stupid Shark Week tabloid tone that pervades so many of these shows. The final section of the program, unfortunately, brings back the sleaze with a vengeance, taking the crew to dive with FIFTY (can you IMAGINE! OMG!) lemon sharks, and attempting to hand feed these “bad tempered predators” that have been implicated in many “attacks on humans”. The eye rolling resumed when one of the dewy-eyed camera-toting token chicks whimpered “I didn’t know if they were going to tear me apart!” That evening, with the “water churning with teeth and fins”, the team attempts to hand feed the lemon sharks (and a tiger shark) once again.

The show concludes (mercifully) with the presenter commenting that it doesn’t seem that humans are on the menu, and that sharks are pretty good at reading the menu whether it’s day or night time.

Shark Bite Summer

This bit of fluff describes the “summer of the shark” in 2001, along the west coast of the USA. Replete with staged attack footage, seas awash with blood, and prurient narration, this is shark attack porn of the worst kind. I confess I couldn’t finish watching it, but suffice it to say that a large quantity of red corn syrup went into the making of this program. It is this kind of trash that unfortunately undoes any good that comes of showing sharks in their natural habitat. Alas.

You can get the DVD here.

Scuba diving and fitness

A recent article from Shape magazine that has been breathlessly circulating in some of the scuba news circles I follow claims that scuba diving is the “new celebrity fitness trend” that “burns tons of calories while tightening and toning your body”. The rest of the article is a thinly-disguised marketing advertorial for PADI, but we’ll overlook that in favour of its ostensible main point: scuba diving will make you fit (and as hot as a Hollywood star).

I’m not a fitness expert by any stretch of the imagination, but I dive quite a lot (a few dives every weekend, weather permitting) and Tony dives even more (a few dives every day, weather permitting). I’d like to make the following observations:

  • One of the things I love about diving is that it can be done by people of almost any body shape and level of physical ability, provided you’re able to help yourself, put together and carry your kit to the water, and display a certain level of watermanship and stamina. As long as this base level of strength and fitness is there and you have none of the medical conditions that are incompatible with diving, nothing precludes you from being a scuba diver. The very regular scuba divers I know – those of whom it could be said that diving is their primary form of exercise – are by no means a uniformly lean and toned group of individuals. Clearly I’m missing something.
  • Diving – the underwater part, at least – is actually mostly about expending as little energy as possible. If you’re using your arms or kicking frantically, YOU’RE DOING IT WRONG! The whole idea is not to get out of breath or to elevate your heart rate (leading to panic). This doesn’t sound like fat-burning exercise to me.
  • Your body does expend energy keeping you warm on a dive – specially in the Atlantic in a wetsuit! The toasted sandwich, chocolate bar, bag of nuts or hot chocolate you consume after the dive, however, replaces all the calories you just burned, plus some. If being cold assisted with weight loss and made you fit, there’d be fewer treadmills and more industrial-sized refrigerators at your local Virgin Active.

Tony and I both had almost a month off diving in January, because he’d had surgery. He returned to work at the end of January, doing three shore dives that weekend. Afterwards, we were both quite stiff and more tired than we usually are after diving, because clearly regular diving does involve some level of conditioning. But what sort of exercise had we experienced? Could two and a half hours underwater really make our muscles feel this way?

The key, however, was that our muscles were stiff. One of the dives was at Sandy Cove, involving a bit of mountaineering. The other two were at Long Beach, and all three were with students. In each case, twelve cylinders and six boxes of dive gear had to be unpacked out of Tony’s divemobile, and at the end of the day packed away again (Tony insists on doing this – he has a “system” and I get in the way!). We had to lift our kit onto our backs, walk to the water, and – in my case – wrestle with a fellow diver’s new BCD and ill-fitting weight belt for 20 minutes while standing in thigh deep water in full kit. After the dive we had to return the way we came. All the exertion took place before and after the dives – the time underwater was extremely slow and relaxing.

If you’re going to get any conditioning from your scuba diving, I think it’ll primarily be in toting 20-30 kilograms of gear around on your back and around your waist, before and after you get in the water. Don’t make the mistake of thinking that diving will fulfill all your exercise requirements unless you’re actually working (e.g. as a commercial diver, a very active archaeologist or a fast-swimming map maker) underwater.

If, like me, you’re a weekend diver, rather than relying on diving to get you fit, it’s your responsibility to make sure that you are fit to dive. Keeping yourself fit to dive would involve doing other forms of exercise during the week to improve your strength and cardiovascular fitness. I’m not saying you won’t get some physical benefit from scuba diving, but it won’t make you look like Jessica Alba or Matthew McConaughey unless it’s your full time job (and even then, perhaps not!).

Shark “research”

It is true to say sharks are in trouble worldwide. Almost any attention to their plight is a step in the right direction. Sadly all too often the attention the sharks receive in the media is of little value to their plight and is purely an attempt to boost the participants’ perception of themselves as “great shark experts”.

This article describes a show that is a perfect example of this. It describes the National Geographic Shark Attack Experiment Live. Does the name make you skeptical? It should. The “experiment” sets out to show little concern for the sharks – a perspex cage was placed in the ocean that a shark would quite likely swim into and risk injury (and I am sure there would be no reporting on this if it happened).

The National Geographic Shark Experiment starts from a premise that comes straight out of Jaws: sharks want to eat people. The only refinement is that the experimenters planned to figure out what garnish they prefer. What is shocking is that the participants are all people who present themselves as being very concerned about sharks. This kind of so-called research is exploitative, tacky, and in poor taste – but, more fundamentally, it does nothing to remove the stigma associated with sharks as mindless predators. It panders to the Shark Week mentality of sharks as ravenous beasts with blood dripping from their jaws, tantalises viewers – exactly as Jaws did – with views of bikini-clad women swimming with apex predators, and has no scientific content whatsoever.

An assortment of other “experiments” were performed, such as dangling a string of plastic beads in front of a shark to prove a bling theory (who thinks this up? no one swims with a pearl necklace on). Once the diver dropped it the sharks followed it down and possibly ate it. The swimming and splashing surfer test was not done near great whites as this would “perk the interest” of any predator… So now reef sharks are no longer predators?

The best for me was diving with a dictaphone and making it seem like this was an earth shattering discovery. Divers dive with all these sharks all the time with video cameras, still cameras, video lights and strobes. What does a dictaphone do differently to all that other electronic equipment? Who swims with a dictaphone, anyway?

Science has proven sharks to most likely be colour blind and use contrast as a visual tool. Dispelling the myth of “yum yum yellow” whilst in a pink bikini is hardly a myth buster. It makes one fairly sure that the “science” was not actually the main feature here.

Pretending that three or four tests done by a single individual can help us to draw any conclusions about sharks is disingenuous and misleading to an often ignorant public who only know what the media tells them about sharks. Real science involves multiple tests, control groups, and the scientific method.

What we already know (real facts by unscientific people): thousands of divers worldwide dive with shiny, dangling scuba gadgets, strobes, cameras, bright shiny regulators, a multitude of brightly coloured fins, masks and wetsuits. Some dive in swimwear with bright shiny silver cylinders strapped to their backs. These people have black skin, pale skin, or bright red sunburned skin. A vast majority of them urinate in the water, their wetsuits and their swimsuits… And you’re more likely to be involved in a car accident on your way to the beach than you are to be bitten by a shark.

And yet, a respected (I think) institution such as National Geographic chooses to associate itself with a television special that takes, as its starting point, the view that sharks are looking for (appropriately dressed) humans to bite. How classy and scientifically up to date.

Guess the dive gear

I often take pictures by accident. This is no mystery – the construction of my camera housing and the fact that I sometimes forget to turn it off on exiting the ocean conspire here to produce curious results. What is a mystery, however, is what some of the photos depict. As a fun (haha) activity for our loyal reader(s), here’s a game of Guess the Dive Gear. Answers at the end of the post…

1. Very easy

We start with something easy
We start with something easy

2. Easy

Also quite straightforward
Also quite straightforward

3. Also easy

What's this?
What's this?

But can you guess what brand it is?

Can you guess the brand?
Can you guess the brand?

4. Slightly less easy

Looks very tropical
Looks very tropical

5. This should be a piece of cake

What's this?
What's this?

Just identifying the piece of gear isn’t enough – do you know the make and model?

Can you guess the brand?
Can you guess the brand?
Still no idea?
Still no idea?

6. A bit tricky

Similar to (4) above, but with an additional item to complicate matters…

Quite challenging
Quite challenging

7. A total mystery

Even I'm not sure what this is
Even I'm not sure what this is


  1. Dangling octo (alternate air source)
  2. Glove
  3. Wetsuit (ScubaPro)
  4. Cylinder
  5. ScubaPro Seawing Nova fins
  6. Cylinder with BCD dump valve next to it
  7. Think I might have been lowering my gear to the ground. There’s a compass visible at the top of the picture, and the black mass at the bottom might be an inflated BCD. Any better ideas?

Newsletter: Wreck penetration and night dives

Hi diving people

Last weekend

Valve handles in dodgy visibility on the SAS Fleur
Valve handles in dodgy visibility on the SAS Fleur

Last weekend we dived the SAS Fleur. This rates as the best wreck dive in Cape Town, in my book. It is closely followed by the MV Aster which we plan to dive and penetrate this weekend. Back to the Fleur: we did not have exceptional visibility (about 6 metres – Clare apologises for the dodgy pictures), and the current was quite strong at depth. But as we were doing a Deep Specialty, on Nitrox, this was a perfect site. We had lots of seals during the dive and many stayed with us during our deep stop and the extended 5 metre safety stop.

Being photo-bombed by seals at the safety stop on the Fleur
Being photo-bombed by seals at the safety stop on the Fleur

After the Fleur we did two dives at Long Beach, being dive 1 & 2 for Open Water students. We visited the new Lady Long Beach reef project being built by Pisces Dive Centre.

Slightly beaten up cuttlefish at Long Beach
Slightly beaten up cuttlefish at Long Beach

Many have heard of the sardine run, well Steve Benjamin from Animal Ocean will be doing a squid run, in Cape St Francis. Diving 25th Oct – 29th Oct (5 days), this is just as the Commercial squid season closes. Visit his website for more info and look at some of the sardine run photos.

Tami approaching a swarm of box jellies at Long Beach
Tami approaching a swarm of box jellies at Long Beach

This weekend

This weekend we are diving in Hout Bay harbour on Saturday morning as part of the clean up dive organised by OMSAC. Diving starts at 9.00 am and even if you are not diving come along and join the fun. The harbour will be alive with divers, boats and humans. This is also a very photogenic part of Cape Town so bring your camera.

If you plan to participate in the cleanup dive, you must register beforehand – visit the OMSAC website for more details.

You must ensure you have your dive card AND your MPA permit with you on Saturday.

Compass sea jelly at the deep stop on the Fleur
Compass sea jelly at the deep stop on the Fleur

We have booked two dives for the afternoon with Underwater Explorers (you may remember Alistair from this post). At 2.00 pm we will do a dive to the Aster wreck, lay lines and do some penetration. Entering the wreck is not for everyone and some of the divers will stay outside while a few of us are inside. We will also attach a few cyalumes as we are doing the second dive there at 6.30 pm.

There is still space on the afternoon dive but the night dive is almost full… Speak up quickly if you want to join. We will be making a day of it so bring chairs, braai stuff and chocolate. We have also ordered sun so bring sunscreen.

There are a lot of people doing these dives on Saturday so it’s important you mail me to book any gear you want to rent. I have bought a few more wetsuits, BCDs, cylinders and regulators so I am sure we will manage but don’t wait until Saturday to let me know what you need – I’ll pack on Friday evening and leave home very early on Saturday. I also only have 6 torches to rent. You can of course go and buy these things from Andre‘s shop in Simon’s Town – email him here!

Sunday we are doing dive 3 & 4 for Open Water and if conditions are good we will dive the Clan Stuart or Windmill. Meeting time will be 10.30 as all my cylinders will be empty from the night dive and I only have one bicycle pump.

Bits and pieces of the Fleur
Bits and pieces of the Fleur

Travel plans

The planning of a Mozambique trip is taking shape and within a few weeks we will have a solid plan. We will most likely go to Ponta Do Ouro and will do the same thing we did for the Sodwana trips: fly to Durban, rent cars and have cheap tents or upmarket chalet options for accommodation. Car sharing, tent sharing and sleeping bag sharing… are all options. If you missed the last two trips then you won’t know how much fun we had but you can read all about it here.

Salps at Long Beach
Salps at Long Beach

(For more information on exactly what a salp is, check out Wikipedia. They’re alive!)


There is a talk by Barry, the owner of Dive Action, at the Dive Action shop next Tuesday evening on diving in Norway with stunning pictures. Free, starts at 6.30pm.

On Wednesday night there is a talk at 7.00pm by George Branch, author of the classic The Living Shores of South Africa and expert on all things marine biology-related, at the Save Our Seas Foundation Shark Centre in Kalk Bay. The topic is evolution, and the cost is R50. (It’s for a good cause and you also get soup and rolls.) Save Our Seas foundation does many things but the Kalk Bay centre focuses on shark conservation. They also have a marine tank that is amazing… You get to see that too. The talks here are always very good and worth the money.

Text me if you are coming to either talk (booking is essential for the Save Our Seas talk) and I will book for you and send you directions. (Well actually Clare will!)


Tony Lindeque
076 817 1099

Diving is addictive!

Dive gear maintenance: Cylinders

Cylinders are made of either steel or aluminium (aluminum to the Yanks), and both are prone to corrosion. Nothing rusts quicker than a damp cylinder. Most people will fill the cylinder with air after a dive, and then store it.

The air we breathe
The air we breathe

When you get home rinse the cylinder well, several times. The plastic boot collects salt and sand but it does not come off easily so drilling a few large drain holes in the plastic at the bottom of the boot makes rinsing easy and the boot does not need to come off so often.

The net protects the cylinder from nicks but once in a while loosen the net and clean away any rust that has formed on scratches (with a scouring pad) and paint the spot. Cylinders require an annual viz, this is a visual inspection for dings, dents, corrosion and general condition. The inside is inspected, for rust, pitting and discoloration. Every four years the cylinder is subjected to a hydro test. This involves filling it with water and pumping it up to a specific pressure, way above the normal operating pressure, and the difference in size is measured to ensure it is structurally sound. The stamp from the hydro inspection is prone to rust and difficult to keep rust-free so as soon as it is returned from inspection you should paint it. If you don’t have any paint, use your (or someone else’s!) clear nail varnish.

The colour of your cylinder is also important. By law (in South Africa) it must be yellow with a grey neck. Compressor operators are not obliged to fill the cylinder if it is the wrong colour, and nor will they fill it for you if it is out of date (i.e. more than 12 months have passed since the last inspection). So painting it random colours will be a problem when trying to have it filled.

The air pumped into a dive cylinder goes through a drying process so there should not be moisture in your cylinder. If you have had a cylinder at depth that has been breathed empty then there is a strong likelihood it has water in it. Should you have moisture enter the cylinder it will rust, and it will do so very quickly. The cure? If it is light rust it can be cleaned with a wire brush (quite a special type of wire brush) attached to a drilling machine.  It can also be chemically cleaned or if really bad it can be ”rumbled”. This is a process whereby the servicing dive centre adds a few handfuls of stones and some water to the cylinder and it is placed on a pair of slow moving rollers that rolls it for some time cleaning off the interior rust. It is then washed, dried and inspected again.

It is not a requirement when servicing a cylinder, but having your pillar valve serviced at the same time is a good policy. If you have the training you can do it yourself but it is best left to the professionals. My cylinders have just had their annual service, a repaint and a pillar valve service. A few new tank nets to replace the badly worn ones and they are all set for a year of trouble free diving.

A long-term test of the compressor

Our compressor
Our compressor

It has been almost nine months since we acquired this little 70 litres/minute compressor. It is Mohnsam compressor unit made in Germany and powered by a 1.9 kW Honda engine. Very compact and well made, it is very portable and has one filling whip. During the time we’ve had it, it has run for a total of 45 hours and has had two services since the service we did when we bought it.

On each service the filter tower has been done, the compressor oil changed and the engine oil changed. The air filter in the motor is a sponge filter which has just been washed each time and the compressor intake has a paper filter element that has been blown clean. There is also a drive belt and a spark plug, but neither of these items have shown any wear and tear

The unit has been trouble free and has proven to be a money well spent. The convenience of being able to fill your own cylinders when you want and where you want to is very beneficial to me and my style of diving. I have filled my cylinders 145 times and this is a saving of around R6,500. I have used a little over 20 litres of fuel on the Honda engine that powers this unit.

When I took my cylinders for their annual visual inspection last month they were in good shape, verifying that this little compressor is pumping clean air, and that frequent drainage is maintaining excellent fill quality.

Dive gear maintenance: Regulators

People often say this is the most important part of your dive gear. It’s not – they are all equally important: take any one item out of the equation and see how lousy your dive is.

One of my regulators
One of my regulators

It is however a sensitive part of dive gear and needs more meticulous care.


If possible rinse and purge your second stages in water whilst connected to a cylinder. If you don’t have a cylinder handy, purge the regulators thoroughly before turning your air off. This helps to blow out sand and water. Remember to dry and fit the dust cap the minute you remove the regulator from the cylinder.

Do not submerge the first stage in water, hold it just above the bath and splash water on it to rinse off any salt or sand. Do not depress the purge buttons on your regulators while you are washing it, as this will allow water to enter the system.

I like to soak the regulators in warm water and rinse the inside of the mouth piece thoroughly whilst connected to a cylinder. Try and rub the inside of your mouth piece with your little finger and feel if its slimy: if it is it needs to be stripped and cleaned.

Water in the system

If for some reason your first stage is submerged without the dust cap, or if you run out of air at depth and water gets into it, it should go for a service as soon as possible as it will be possible for a service technician to strip, clean and re-assemble it. If you leave it for a while it will need a service kit and occasionally some parts will require replacement if they have become corroded.

Many people believe that a quick fix for a submerged first stage is to connect it to a cylinder, turn on the air and depress both purge buttons for several minutes. This is utter rubbish: while it may remove some of the moisture, the high volume of air will drop the temperature inside the pillar valve and first stage resulting in more moisture content than you started with. The big issue is that the second you open the cylinder the system is charged with the high pressure port then opened and all the water will go directly to your pressure gauge capillary tube and this will be the beginning of the end for your pressure gauge.

Clean air: all about compressor maintenance

Diving, in my opinion, is one of the most rewarding sports on the planet. Breathing underwater, interacting with the myriad of creatures you can and do always encounter and the total tranquilty below the surface cannot be achieved easily in any other sport. If it is an adrenaline rush you need, diving can give you this too. Having raced cars, bikes and go-karts I know what an adrenaline rush does for you, but believe me an encounter with a whale shark, a pod of dolphins, a tiger shark, hammerheads or a great white shark give you a rush unlike anything else, so diving gives you the best of everything.

As with any sport or recreational activity diving has a few inherent risks. Besides regular maintenance of your gear, the air you breathe underwater must be clean and pure. A cylinder filled with contaminated air will harm you quickly and quietly. Unless you test each and every cylinder you breathe from with a sophisticated analyser for air quality you have no idea of how good your air is.

Charcoal, used felt pads, new pads, and drying agent
Charcoal, used felt pads, new pads, and drying agent

All dive centres have a strict policy on compressor maintenance and filter changes or services but occasionally you will have a fill from an operator who is not that scrupulous. You may also have a fill from a privately owned dive compressor and again the same regulations regarding maintenance apply. If you are unsure, ask the compressor operator for his certification card and the compressor service records. This is your right, it is you that is going to breathe that air. A rule of thumb for me is that if the owner dives and breathes that air then it is most likely safe, but if the owner is seldom breathing from the cylinders he supplies then there may be a risk.

Components (felt pads etc) from inside the filter tower
Components (felt pads etc) from inside the filter tower

I often fill my own cylinders, for my students, divers and myself. I am a stickler for the quality of the air I want in my cylinders so I am careful of the places I will fill my cylinders and just as careful of the quality of the air I pump. Our compressor has a service interval of 15 hours and this is what is involved.

The filter tower is made up of a few components. Felt pads between the water separator, charcoal and drying agent. The filter tower also has a bleed valve and bleeding the moisture off every few minutes helps in reducing the moisture the filter must remove. The compressed air passes through the water separator, a felt pad, a drying agent, another felt pad, charcoal, and finally another felt pad before it enters the cylinder. This ensures dry clean air is pumped into the dive cylinder.

Water separator inside the bottom of the filter tower
Water separator inside the bottom of the filter tower

There are other considerations.

Air intake
Air intake

The intake of air to the compressor needs to be clean so a particle filter on the intake pipe is important as is the location of this filter This prevents bugs, sand , dust and paper entering the compressor. The compressor we have has a petrol engine and the exhaust fumes must be kept away from the intake so it is important to position the intake upwind of the motor.

The top of the filter tower
The top of the filter tower

The compressor runs on a synthetic oil that must be changed as often as the filter contents and the Honda engine also has service requirements. Spark plug change after 30 hours, air intake every 15 hours and an engine oil change every 15 hours. The whip or filling hose needs a cap to keep the threads clean and the opening free from contaminants.

A record of the fills done must be maintained and the correct procedure followed. This includes recording the last viz date, owners detail, ending pressure and blend if it is a Nitrox cylinder.

Finally, to operate a compressor requires a certification and in South Africa this must be a course approved by the department of manpower. The CMAS compressor operator course offered by False Bay Underwater Club fullfils these requirements.

CMAS Compressor Operator certification card
CMAS Compressor Operator certification card