UKRS FAQ

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uk.rec.scuba Frequently Asked Questions

Author: Alasdair Allan (aa@ukrecscuba.org.uk)
Contributions: Nigel Hewitt, Luke Cornish, John Brett, Keith Lawrence, Benjamin Panter
Last-Modified: 13-MAR-2003
Version: HTML v2.1.0

Welcome to uk.rec.scuba (UKRS). This newsgroup is for the discussion of all aspects of SCUBA diving in the United Kingdom (UK), including diving equipment, diving locations and forthcoming diving trips. The content may be of a technical nature and posting of hints, tips and advice is positively encouraged. The group forms part of the UK heirarcy and as such discussion is UK orientated, for general discussion of SCUBA topics you should look in the rec.scuba, rec.scuba.equipment and rec.scuba.locations newsgroups where you will find discussions that have a more international feel. Just so long as your idea of international means American...

Additions, comments and corrections are welcomed and should be mailed to the FAQ maintainer, Alasdair Allan (aa@ukrecscuba.org.uk).


Table of Contents
0. THE FAQ
0.1 Where can I obtain the latest copy of the FAQ?
0.2 Is there a ASCII or HTML version?
1. GENERAL
1.1 Is there a UKRS website?
1.2 Is there an archive for the group?
1.3 I've got a great GIF, I'll just...
1.4 Do I need training?
1.5 Is it dangerous?
2. TRAINING
2.1 How do I become a diver?
2.2 Which training agency is best?
2.3 Okay, so which training agency should I use?
2.4 What's the training like?
2.5 Where can I learn?
2.6 How much does it cost?
2.7 How long does it take?
2.8 I'm going somewhere warm, is it worth me taking a course before I go?
3. MEDICAL
3.1 I can't see without my glasses, can I dive?
3.2 Surely asthma doesn't stop me diving, does it?
3.3 I said I suffer from asthma, can I dive?
3.4 I'm registed as disabled, can I dive?
3.5 They say I'm too young, why does age matter?
4. UK SPECIFIC
4.1 What's it like diving in the UK?
4.2 I trained on holiday, can I dive in the UK?
4.3 I trained in the UK, can I dive on holiday?
4.4 Will you take me diving?
4.5 You guys do decompression diving? But thats suicide!
4.6 Okay, can I do a decompression dive?
5. EQUIPMENT
5.1 What's in those tanks on your backs?
5.2 So what is Nitrox then?
5.3 Is all that equipment expensive?
5.4 What equipment should I buy?
5.5 Whats all the fuss about Spare Air?
5.6 What is this A-clamp or DIN business all about?
5.7 Should I go for 300 bar or 232 bar bottles?
5.8 Independent or manifold twinset?
5.9 What computer should I buy?
5.10 Should I get a drysuit? Or a semi-dry?
5.11 Whats the fuss about auto-dump valves?
5.12 The difference between static and dynamic pressure?
5.13 What the heck is DIR? or the Hogarth Configuration?
5.14 How can I build an interface to connect my Aladin to my PC?
5.15 How about my Suunto?
5.16 Do you know where to find decompression/tide plotter/log software?
5.17 Is there any software for my PalmPilot or Psion?
5.18 But I'm running Linux!
5.19 How to I fit a new seal to my drysuit?
5.20 How do I work out how much weight I need?
5.21 How much does air weight anyway?
5.22 What the fuss about Nitrox and Oxygen Cleaning?
5.23 What is a DSMB (Delayed)?
6. MISC
6.1 What is a "stroke"?
7. PEOPLE
7.1 Is there a list of people that participate on UKRS?
7.2 Who is Keith Lawrence?
7.3 Who is Alasdair Allan?
7.4 Who is George Irvine?
7.5 Who is on the UKRS web team?
7.6 Who is what's their name...?
8. DISCLAIMER

0 THE FAQ

0.1 Where can I obtain the latest copy of the FAQ?

The latest version of this document can be obtained via the web (HTTP) at http://www.babilim.demon.co.uk/pages/ukrs/faq.html.


0.2 Is there an ASCII or HTML version?

You're reading the HTML version, the ASCII version can be found at http://www.babilim.demon.co.uk/pages/ukrs/faq.txt.


1 GENERAL

1.1 Is there a UKRS website?

The UKRS website can be found at http://www.ukrecscuba.org.uk/ and is maintained by Keith Lawerence (keithl@ukrecscuba.org.uk) and the rest of the UKRS web team (see section 7.5). The site has further information, including the formal charter for the group, and an extensive links section.


1.2 Is there an archive for the group?

No. However the group is archived at Google (http://groups.google.com), along with just about every other USENET group. Selected postings may be missing as some (many?) people object in principle to news group archiving and hence add an X-NoArchive: header line to their postings to prevent them being added to the archive.


1.3 I've got a great GIF, I'll just...

No! From the charter "The posting of binary files is not allowed on this group and should be reserved for binary specific newsgroups." See the web page ( http://www.ukrecscuba.org.uk/) for further details.


1.4 Do I need training?

Yes, very much so. Diving is a technical sport, you not only need practical training in how to operate your dive gear, you'll need some basic theory as to how your body is going to react to the stresses your going to put it under. Training is not optional, please don't dive without it.


1.5 Is it dangerous?

Every year people die while SCUBA diving. A record of incidents in the UK is compiled by the BSAC in the NDC Diving Incidents Reports. Reports from 1989 are avialable at http://www.chime.ucl.ac.uk/~rmhiajp/diving/ndcrephf.htm.

SCUBA diving can be dangerous, thats why you need training, and why when you have been trained you should make every effort to continue to practice your skills. To put things into perspective, though there are several deaths each year, given that there are many tens of thousands of active divers in the UK, making hundreds of thousands of dives each year, the headlines in the papers can be misleading. Like any adventure sport diving is as dangerous as you personally want to make it, you are probably at more risk driving to the dive site than actually diving.


2 TRAINING

2.1 How do I become a diver?

By taking a recognised training course that lead to your certification as a scuba diver. There are four main agencies offering training in the UK

The British Sub-Aqua Club (BSAC) http://www.bsac.com/
Professional Association of Diving Instructors (PADI) http://www.padi.com/
The Sub-Aqua Association (SAA) http://www.saa.org.uk/
The Scottish Sub-Aqua Club (SSAC) http://www.ssac.co.uk/


2.2 Which training agency is best?

Oh boy. Lets not start that arguement, suffice to say this is a matter of some debate between those of us who are affiliated to the different agencies.

The BSAC is the 'traditional' face of UK diving, mainly club based (although there are commercial schools) with training carried out by volunteer club members. The training scheme has been traditionally geared towards UK diving conditions. However the training scheme has recently been reviewed, and the resulting changes led to much (ongoing) debate amoungst BSAC members, with not everyone being entirely happy with the result.

PADI is an American based commercial organisation offering a standard level of training throughout the world, at present there is a limited club structure. The training is broken down into smaller modules than the BSAC/SAA training. This is the quickest way of getting in the water. The PADI entry level qualification PADI Open Water (OW) is probably not sufficient for diving in UK conditions. The next level up, PADI Advanced Open Water (AOW) is probably the minimum anyone would recommend for UK diving.

The SAA is club based training similar to BSAC but this time by a network of Independent Diving Clubs with the SAA providing an umbrella structure. SAA policy is also welcoming of divers trained under other recognised systems.

The SSAC is again club based training system similar to BSAC/SAA. They seem to keep their heads down, although my understanding is that their entry level qualification is to a much higher minimum standard than the other training agencies.


2.3 Okay, so which training agency should I use?

You ask some difficult questions don't you? If all you want to do is dive when you are abroad on holiday and are not interested in UK diving then the basic PADI course is the one for you. However, if you would like to dive in the UK then BSAC/SAA/SSAC may be a better long term investment of your time as you immediately acquire a bunch of people that you can go diving with...

However, its very important to note that the quality of training depends on the the instructor, and not on the agency that licensed them.


2.4 What's the training like?

First of all you do not have to be a super fit swimmer to learn to dive, you will have to show that you can swim a few lengths, duck dive and tread water but that's about all. Training is in three main parts, theory, pool work and open water diving. There is some classroom learning where you will be taught about the things that affect you like pressure and a little diving medicine, in the pool (or sheltered shallow water) you will be taught basic diving skills like using the equipment and clearing your mask, then finally you will be taken on "real" dives in a lake or at sea.


2.5 Where can I learn?

There are places to learn all over the country, all over the world in fact. For a geographical list the best UK one is on Greg Roach's site (http://www.subaqua.co.uk/).


2.6 How much does it cost?

A basic commercial course is around £200, but you get what you pay for, go on recommendations. If your going to invest in equipment start with only the basics of mask (£30), snorkel (don't pay more than £8) and fins (£25). For inital training both in the pool and in open water rent your equipment, this should be inclusive in the cost of the course. If you go via the club route training costs less, but your expected to aquire your own kit more quickly.


2.7 How long does it take?

Four or five days for a basic comercial course, longer if you learn in a club.


2.8 I'm going somewhere warm, is it worth me taking a course before I go?

You probably don't want to spend your holiday inside a classroom doing theory work so it might be a good idea to do this beforehand in the UK. Both PADI and BSAC run "referral courses" where you can do your theory and pool training in the UK and the open water part of the course abroad somewhere nice and warm.


3 MEDICAL

3.1 I can't see without my glasses, can I dive?

Yes! There are several options open to you. Most dive shops stock (or can easily get) a range of the 'standard' prescription lenses that just fit into a mask replacing the normal lens. More complex prescriptions (including bi-focals) can be made to order to either replace standard mask lenses or be bonded to the inside of a standard lens. Many divers wear their contact lenses, although this can cause problems if you loose one.

I've even heard of a case of a diver who gets the staff at Stoney Cove to look after her guide dog while she's diving.


3.2 I suffer from a medical condition, can I dive?

To learn to dive you will either have to undergo a medical or at least answer a medical questionnaire, there are a whole host of conditions (e.g. asthma) that would seem to preclude you from taking up diving. However, with all medical conditions there are 'shades of', just because you can't tick the correct box it doesn't mean that you can never dive. If you have such a medical condition then you must consult a doctor who understands diving medicine, the BSAC and SAA have a list of medical referees (doctors) who specialise in this. You will need to see one of these referees and ask them if you can dive, if they say 'OK' then you will get a medical certificate that says so. Do not be tempted to just lie to pass the medical, diving puts a special type of strain on the human body and you will not only endanger yourself but other people you will be diving with.


3.3 Surely asthma doesn't stop me diving, does it?

Asthma is a medical condition that may preclude you from diving (see 3.2). In general if your asthma is brought on by exercise then you stand a poor chance of passing the medical. However as always there are shades of grey, you should seek advice from a medical referee. No one will give you medical advice over the internet, if they do you certainly shouldn't listen to it. On the other hand some further information about this commonly asked question can be found at http://www.mtsinai.org/pulmonary/books/scuba/asthma.htm.


3.4 I'm registed as disabled, can I dive?

Disabilities do not necessarily preclude you from diving, most can be overcome. I've dived with people who are registered disabled. The best advice is to seek out a medical referee and an understanding club. A good source of information is the Scuba Trust, http://www.scubatrust.org.uk/.


3.5 They say I'm too young, why does age matter?

There are no definitive studies that demonstrate that diving as a child can be harmful to future development, and due to the ethical problems such studies would raise, there probably never will be any such trials carried out. There is however some circumstancial evidence which suggests that taking up SCUBA diving too young may cause later health problems, see http://www-personal.umich.edu/~lpt/kids.htm for details.


4 UK SPECIFIC

4.1 What's it like diving in the UK?

You remember those wonderful pictures of the on TV, of clear blue seas and divers in wet suits swimming though clourful coral forests surrounded by multi-coloured fish? Yes? Well, its nothing like that. Its colder, darker and the visibility is usually much less (although it can at times suprise you). Why do we do it then? It can be very rewarding, UK waters are some of the best in the world for wreck diving, the feeling of decending a shot line down onto the deck of an wreck, turning on your torch and startling a lobster out of its hole is hard to describe. You glide along the deck towards the wheel house shining your torch into passing portholes, stopping to look at some piece of wreckage. Its a very different sort of diving that you'll get abroad in warmer climes. You just have to try it...

The reduced visibility also means that we dive differently here in the UK than in warmer climates. In warm seas diving is mainly in escorted groups led by experienced divers, in the UK we normally dive as a two person team (known as a buddy pair), each diver being fully trained in navigation, rescue etc. That is why the UK based training agencies take longer to train a basic diver, there is more to learn.


4.2 I trained on holiday, can I dive in the UK?

Maybe! Due to the differences is UK conditions when compared to holiday destinations you are probably not prepared for what you will encounter. If you have gained a recognised diving qualification abroad you can go diving in the UK, but don't expect to go out on the dive boats to the wrecks straight away, you will have to become familiar with UK conditions and do some shallow familiarisation dives and possibly a bit of training first.


4.3 I trained in the UK, can I dive on holiday?

Yes. UK training, and more importantly experience diving in UK waters, is recoginsed world wide. I remember the first time I dived abroad, in Australia as it happens, I entered the dive shop (a PADI centre) and with some amount of trepidation put my BSAC qualification record book down on the counter. No problems, in fact after another couple of BSAC trained divers turned up, the owner said something along the lines of "BSAC divers? You'll be swimming in formation with your eyes closed then?" I've seen other British divers, not necessarily BSAC people, recieve similar receptions.


4.4 Will you take me diving?

Could do! UKRS started out as a discussion forum, but back in 1999 some of us got bored with just talking about diving. The first official UKRS dive weekend was arranged by Keith Lawrence and held on the 8th and 9th of May 1999 in Portland.

Since then we've run over 60 trips. The up-coming 2003 season will push us past 85. More information can be found on the UKRS web pages, see http://www.ukrecscuba.org.uk/ukrsdives/ for more details.


4.5 You guys do decompression diving? But thats suicide!

Decompression diving is quite common in the UK. You'll find lots of people on UKRS that commonly carry out decompression dives, you'll find many people that use nitrox as bottom, travel or decompression gas. You'll probably even find some people using trimix. The peculiar legal system in the US means that decompression is regarded as "...being considered akin to wandering down the middle of the M4 at 6.30PM on a Friday evening singing `Flower of Scotland' and waving a bunch of petunias around your head" (Jason Sheppard, 1997). Lets just say that the UK attitude is somewhat different...


4.6 Okay, can I do a decompression dive?

Erm, maybe. If you have the correct training, and if your carrying the correct equipment then the answer is yes. If you don't have the correct training, or you are inexperienced, or you don't have the correct kit. The no, please, don't try doing decompression dives. Your asking to get yourself bent. Decompression diving isn't for everyone, your boyancy has to be spot on, you need to be able to plan your dive and then actually stick to the plan, you must carry an alternative air source (AAS) such as a pony clylinder or (better yet?) a set of independent or manifold twin cylinders.


5 EQUIPMENT

5.1 What's in those tanks on your backs?

Most commonly the answer is air. Cleaned, filtered and compressed to 200 or 300 times atmospheric pressure, but still air. Despite press reports to the contratory, the use of pure O2 is restricted to decompression gas only.


5.2 So what is Nitrox then?

Normal air is roughly 20% Oxygen, 80% Nitrogen, a Nitrox mixture (normally called a mix) alters this percentage. For ordinary diving mixes of 32% O2, 68% N2 through to 50% O2, 50% N2 (for deco) are common. When talking about Nitrox mixes the normal abbreviation used is something like EAN32, EAN stands for Enriched Air Nitrox, the number 32 stands for the O2% in the mix.


5.3 Is all that equipment expensive?

Whilst you are training the equipment should be provided for you, when you are qualified you can rent equipment from many places. Most regular UK divers have their own equipment, start looking at £500 for a full set of second hand gear, I doubt whether many UK divers of more than two years experience have less than £1,000 worth of equipment.


5.4 What equipment should I buy?

Hard to say, what sort of diving are you thinking of doing? What sort of training have you had, what sort of training are you thinking of doing in the future? Do you think you'll start using Nitrox withing the next couple of years?

My best advice is not to buy anything straight away. Go diving, rent some gear, see what feels comfortable. Above all, talk to your fellow divers.


5.5 Whats all the fuss about Spare Air?

Oh boy, time to break out the asbestos suit. Spare Air has brought about alot of debate on rec.scuba and rec.scuba.equipment, fortunately the on-going flame wars have touched UKRS only lightly.

A Spare Air is a "bailout bottle" available in sizes as small as 1.2 cu ft, and as large as 3 cu ft (The cubic foot being the, somewhat quaint, way the Americans size their cyniders). The bottle has integral regulator that must (for older models) be switched on before use. Bailout bottles can cost between £120-200. A Spare Air should not be mistaken for the emergency bottle often found on UK made Stab Jackets (such as the AP Valves models), which in theory can be used (after proper training, and only in an emergency!) to inflate the Stab Jacket at depth and bring you to the surface.

So why does the Spare Air come in for so much flack from the USENET community? Well, its the generally held belief that the Spare Air doesn't hold enough gas to be an effective bail out option for the sort of diving normally undertaken in the UK. The arguments can get somewhat heated at times...


5.6 What is this A-clamp or DIN business all about?

DIN is pretty much accepted by most people as being the more secure system, the O ring is captured and is less likely to extrude than with an A clamp system, which would lead to a gas leak.


5.7 Should I go for 300 bar or 232 bar bottles?

It depends! Its very hard to find anyone that will fill 300 bar bottles, and bearing in mind that the gas laws go non- linear about 220 bar you aren't really gaining as much extra gas as you might think (even if you can find someone to give you a fill that actually reaches 300 bar). In practice it might be simpler to buy a 12l rather than a 10l, or a 15l instead of a 12l. Or even starting thinking about a twinset if you need more gas than your currently carrying.

If your a nitrox diver you almost certainly don't want to consider 300 bar cylinders, due to the non-linear nature of the gas laws above 220 bar, as it makes gas mixing more of a lottery than a science. See my article on the gas laws, http://www.babilim.demon.co.uk/pages/gas_laws/, for a more detailed explanation.


5.8 Independent or manifold twinset?

If you want to follow DIR (see section 5.13) you want a set of manifold twins, with a wing and metal backpack. However, many people in the UK dive on independents. At times the arguments between the two factions can become heated.


5.9 What computer should I buy?

This is another hot topic, with as many answers are there are people. In general however people seem to fall into two main camps. People are either pro- or anti- air integrated computers. My personal position on this is very clear (have a look at the Google archives and it'll be obvious). As one of the partisans, and someone that can't resist posting on the subject every time it comes, up I probably can't be trusted to give an unbiased view.

In general however, there are two main "brands" of dive computer on sale in the UK these being Uwatec (Aladin) and Suunto. Both have there ups and downs. A good idea is to get a computer similar to that used by your dive buddy, as different makes may (will) have different ascent rates and decompression algorithims. From my own experience I'd advice anyone against buying the basic no decompression model (e.g. Aladin Sport) as decompression diving is so common in the UK that using a computer which won't report your current deco obligation may undely complicate things for both yourself and your buddy.

Just a reminder however, dive computers are no substitue for good dive planning, a set of tables and knowing how to use them. Computers can and do fail. You have been warned...


5.10 Should I get a drysuit? Or a semi-dry?

Some people seem to get by in the with a semi-dry, but the majority of people (including me) who dive regularly in the UK use a drysuit.


5.11 Whats the fuss about auto-dump valves?

Some people love them (I do), some people think they're the worst invention since the last invention they didn't like. An auto-dump, usually set on the upper arm unlike a manual cuff dump, does just what it says. It controls the amount of air in your suit automatically dumping excess so that the air in the suit stays at ambient pressure.


5.12 The difference between static and dynamic pressure?

Moving an object through the water requires more force than moving it through air. This force shows as an increase in pressure on the side that is forcing the water away. This is usually not significant to divers except when we jump in from a jetty or the back of a boat and hit the water at some speed.

However the term 'dynamic pressure' is used as an excuse to explain why a watch that is apparantly rated to 50 meters leaks in a swimming pool and the manufacturer then crys out on the warrantee claiming missuse. (Read the small-print: 50m = can be worn in the rain, 100m = can be worn swimming, 200m = can be worn snorkeling)


5.13 What the heck is DIR? or the Hogarth Configuration?

DIR, also sometimes known (incorrectly) as the Hogarth Configuration stands for "Doing It Right". The basic concept is that for each piece of kit you carry and procedure you follow there is one way of doing things, the right way. The system originated with the WKPP cave diving group, http://www.wkpp.org/, and there are many web sites (for instance http://www.gasdiving.co.uk/) that set out to explain it far better than I could do here.


5.14 How can I build an interface to connect my Aladin to my PC?

This is actually quite easy to acomplish with only modest skill at electronics. If you can solder two bits of wire together without melting your fingers then you can build the Aladin interface for about £5. You can find further information, and detailed plans on several web pages listed in the Dinving Software and Dive Computers secrtion of the links pages on the UKRS web pages, see http://www.ukrecscuba.org.uk/links/links04.html#Diving_software_and_dive_computers for a full list.


5.15 How about my Suunto?

The Suunto interface is a bit more challenging, but still quite within the reach of the amateur if you have access to PCB etching equipment. Again information about building the interface can be found in the UKRS links section.


5.16 Do you know where to find decompression/tide plotter/log software?

Software? Again, look in the UKRS links section.


5.17 Is there any software for my Palm or Psion?

Yup, again you can find information about how to connect an Aladin dive computer to your Palm and Psion in the UKRS links section.


5.18 But I'm running Linux!

This doesn't present major problems, see http://pakuro.is.sci.toho-u.ac.jp/aladin/index-e.html for details of how to connect your Aladin to your Linux box.


5.19 How do I fit a new seal to my drysuit?

Place a washing up liquid bottle filled with water up the sleeve, place the seal over the suit (and bottle) so that it fits in place exactly. Use several rubber bands, placed ontop of the seal to holid it in place just above the end of the seelve. Mark on the suit with a pencil or chalk where the seal comes upto and roll the seal back, so that both glueing edges are exposed, and you can see the bottle underneath (Check that the seal fits it place when you roll it back). Place some paper under the now turned back edge to protect the rest of the seal from glue overspill, and apply glue to seal and suit. Take some care with this and be sure to glue right up to the fold in the seal so the glue will extend just beyond the suit when the seal is rolled down. Glue up to the line you marked on the sleeve. Let it touch dry, and repeat. Roll the seal down over the suit, and it will fit exactly (you've already checked it!). Use a roller (or can) to press the materials together. Let the glue cure for a bit before removing the bottle - empty water first.

The latex only curls when the glue is wet, so if your quick you can apply the glue before the latex curls. Once it's touch dry you can straighten the seal out if neccessary. The paper under the seal helps you with speed as you don't need to be as careful. As the glue is contact adhesive, you don't need to complete the whole process before if dries, it will still glue when touch dry (as long as you don't leave the glue for hours).


5.20 How do I work out how much weight I need?

At the start of dive, with all cylinders full, and all ditchable equipment present you should be able to stay comfortably on the surface with head out of water. At maximum depth you should be able to attain neutral bouyancy, and at the end of the dive with all cylinders on reserve and all ditchable gear gone you should be able to hold your 3 or 6m stop comfortably.

Taking them in reverse order, the last point is the one to start with, and most important in setting your weighting.

The second point splits into two parts: (a) Loss of bouyancy from compression - typically wearing a neoprene suit. Membrane or crushed neoprene drysuits don't suffer from this problem. (b) Weight of gas. Air weighs ~1.2g/litre, and you know the volume and pressure of your cylinders, so you can work out the weight of gas you are carrying.

The first point is about safety and comfort. The head requires from 4lbs (face only) to ~18kg (entire head/neck) lift to bring it out of the water. If you have a liftbag/DSMB, this can be used in conjuction with wings/suit to achieve this lift in an emergency.

Finally, ditchable equipment is anything you might want/have to leave behind. An example being any porthole removing tools. For obvious reasons, this should be kept to a minimum. This also includes stage cylinders, which is why you should not use negatively bouyant stage cylinders (e.g. steel 10s).

If you now work out the total amount of bouyancy compensation you need during a dive (having weighted yourself correctly in the first place), it works out to a pretty small number (far less than the 80-100 lbs lift superwing stuff).


5.21 How much does air weight anyway?

The weight of air can be easily calculated

Temperature Weight
oC kg/m3 kg/l
0 1.293 0.001293
10 1.247 0.001247
20 1.205 0.001205
30 1.165 0.001165

Air in a cylinder = Pressure (P) * water capacity (Wc)

So the weight (at 10C) = ( 0.001247 * P * Wc ) i.e. in a set of twin 12's pumped to 232 bar and then breathed down to 50bar we would loose the following weight 0.001247 * (232-50) * 24 = 5.44 kg

A script is available which will calculate the bouyancy of your cylinder, both full and empty, written by Greg Roach it can be found at http://www.subaqua.co.uk/cgi-bin/cylinder-buoyancy.cgi.


5.23 Whats the fuss about Nitrox and Oxygen Cleaning?

When divers start to increase the oxygen percentage in their breathing gas to reduce the amount of decompression they need there are more complications than just the fact that oxygen becomes toxic at depth.

Pressurised oxygen can easily convert the barely flammable into a very combustible mix (eg: add saltpetre (oxidant) to charcoal and you convert black barbecue fuel into gunpowder). Add high pressure oxygen to rubber O-rings and.... well you get the message.

Once you go above 40% oxygen the effects accelerate as the inert gas fraction falls steeply so we need to change to low flammability materials and especially lubricants. This is called oxygen service and involves using suitable materials for the job. With tanks you always use Oxygen service materials even if you are only using sub 40% mixes as, in the UK, they are normally made by pumping a measure of pure oxygen into the tank and then filling with clean compressed air. The tank valves and seals get a dose of 100% O2 and need to be the right stuff.

Once that has been done the equipment needs to be protected from further contamination by materials that could become inflammable, that is oils and greases. There is an arbitrary standard that calls for a cleaning procedure every year to remove any contamination and in the days of oily compressors this may have been a good practice but it is now being called into question. That said: if you suspect contamination get it cleaned.


5.23 What is a DSMB (Delayed)?

A Delayed Surface Marker Bouy (DSMB), as opposed to a Surface Marker Bouy (SMB) or a "safety sausage" more commonly used in the States, is an essential piece of UK diving kit. In the UK it is common practice not to return to the shot line at the end of a dive. Assents are usually done using a DSMB which has been stowed through the dive and only inflated at the end, usually at the bottom.

Practice using a DSMB, get somebody to show you how. There are far to many cases of divers being dragged upwards when they deploy the DSMB incorrectly. So a DSMB is an essential bit of kit, but it must be used properly.

Some information about DSMB storage can be found on the UKRS web site at http://www.ukrecscuba.org.uk/ukdiver/dsmb/.


6 MISC

6.1 What is a "stroke"?

A "stroke" is a slang term used by divers that follow DIR (see 5.13) to refer to a diver that isn't following DIR. In general divers that dive strictly by the DIR method regards other methods of kit setup as "dumb".


7 PEOPLE

7.1 Is there a list of people that participate on UKRS?

Recently Jason Poynting started to maintain a UKRS Who's Who list, see http://www.scuba-addict.co.uk/who/.


7.2 Who is Keith Lawrence?

Keith Lawrence (keithl@ukrecscuba.org.uk) is the father of UKRS and was one of the proposers of the group. He maintains the group website and due to his numerous postings to the group acts as a sort of unoffical referee. Keith is also somewhat infamous for arranging the first official UKRS dive weekend, and apparently for snoring quite loudly.


7.3 Who is Alasdair Allan?

Who me? My name is Alasdair Allan (aa@ukrecscuba.org.uk) and I accidently volunteered to maintain the FAQ you've just been reading. If you disagree with anything I've said tell me, I'm open to suggestions and corrections.


7.4 Who is George Irvine?

George M Irvine III is the project director for the WKPP (http://www.wkpp.org/) the people that developed DIR/Hogarth (see 5.13). Funnily enough being an American he doesn't hang out on UKRS, but people keep on asking who he is anyway.


7.5 Who is on the UKRS Web Team?

The UKRS website, FAQ and other web presence is maintained by the UKRS web team, which consists of (in strict alphabetical order) Alasdair Allan, Gordon Henderson, Nigel Hewitt and Keith Lawrence.


7.6 Who is what's their name...?

Erm, I don't know. Or, maybe I do, I haven't been paying much attention. If you think someone (you perhaps?) should be listed here tell me...


8 DISCLAIMER

I disclaim all liability for material included in this document. While every care has been taken to keep the material in this FAQ correct, I take no responsibility for any liability arising from material that proves to be factually incorrect or misleading. I also disclaim any liability for actions taken as a result of explicit or implicit information and/or advice contained in this document, or any resulting physical or financial consequences of these actions. SCUBA diving is a dangerous sport and this document is no substitute for proper training. All trade marks are recognised.

Anyway, I've got an overdraft, there isn't any point in sueing me...

Copyright © 1999-2003 Alasdair Allan

Copyright is reserved. I grant to you such licences as are required for you to read, copy and store this document for non-commercial purposes. No further or other licence explicit or implied is granted.


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