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* A number of FAQ’s are answered by ASSET Guidance Notes.
The HSE also publish Diving Information Sheets which can be downloaded at http://www.hse.gov.uk/pubns/diveindx.htm
For advice and guidance to questions not answered here, ASSET members can contact the ASSET Technical Coordinator at techspert@aol.com
When using this facility, please state your full name and ASSET membership number(s).
Note:  Any references to “the Law” or health and safety, relate to the UK, unless otherwise stated.


Q. Do you need a certificate of competence to O2 clean cylinders and regulators but not to do O2 fills?

A. the law is not specific about requiring certification. It does however require "competence", as a general requirement, to do anything at work. With no specific definition in health and safety law, it is often left to industry organisations and ultimately the courts to define what competence is or should be.
So to answer your question: you're not required to have a certificate to do anything but you are required to be competent!
From the individual’s point of view, how can they demonstrate competence? Firstly, they need to show that they have had adequately training. This is where ASSET training and certification comes in. We set out and deliver, what we believe to be, the best training available and make efforts to get the industry and, more importantly, the HSE on side. We believe that we have the confidence of the HSE because they send all their inspectors on our courses (which they wouldn’t do if they thought our courses were inadequate)!
The law further loosely defines competence as "both trained and experienced". You can only gain experience over time. In our industry, we seldom have the opportunity to gain field experience under supervision, leaving the newly qualified technician working alone so it's really important to be thorough and avoid errors, especially whilst gaining initial experience!

CYLINDER MARKING (stamping, colours and labels)

Q. We recently had a cylinder for filling that was stamped for a visual Inspection but which had the letter “V” obliterated to convert it from a visual inspection to a Hydraulic test so we refused to fill it as a suspicious alteration. When contacted, the test station said that they had obliterated the “V”, when the customer changed their mind, after they had completed the required visual inspection and asked for a hydraulic test to be carried out. Is this correct practice?

A. No. if this became acceptable practice; there would be nothing to prevent individuals from obliterating the letter “V” thus converting every visual inspection mark into a hydraulic test!
Good practice, whenever there is an error or a change required in stamp marking is to obliterate all of the original marks and completely replace them.

Q. I’m told that if a Scuba cylinder is overdue for a visual inspection it must have a hydraulic test instead. Is this correct?

A. There is nothing in the standards which explains what to do if a visual is late. Bearing in mind that a late visual stamp can't be used to post-date a hydraulic test, the label should be punched out to indicate when the next hydraulic test is due. Therefore, by the book, if a visual is late e.g. 6 months, the label should be punched to show that only 2 years remain until the hydraulic test is due.
However, a custom has developed in the industry that if a visual is late, the test station insists on carrying out a hydraulic test. This is custom and practice, it is most definitely not in the standards.
The argument for this practice is that if a label becomes detached, the filler is left with only the (late) visual inspection date, stamped on the cylinder, to indicate when the next hydraulic test is due. This would give a false indication of when the next hydro is due.
Certainly, if a visual inspection is as much as 6 months overdue, it would be prudent to carry out a full inspection and hydraulic test, both as a precaution and to prevent the above confusion.

Q. I have recently had a cylinder hydro tested by a local test station.  When I collected the cylinder I noticed that the test mark had been suffixed with a "V" for a visual test.  When I pointed this out to the test station they merely blanked out the V with three horizontal dashes, leaving the rest of the stamp in place.

I recall being told, on the DITC, that incorrect marks should be completely obliterated with a series of X's and the cylinder re-stamped.

A. You are correct. What they've done could be interpreted as an unauthorised attempt to turn a visual mark into a hydro mark. The Test Station should obliterate the complete mark and re-stamp it.

Q. Can you confirm that there is a legal requirement to paint coloured quarters on cylinder shoulders?

The reason for this question is there is a test station that re-paints cylinders and does not add the shoulder colours.

A. With regard to cylinder colours:
EN 1089-3 only requires a colour code on the shoulder and, so long as the shoulder is coloured then, the body colour has no meaning. However, if the shoulder is not correctly coloured, the body colour implies the contents. For example, a Yellow cylinder with Black/White quartering on the shoulder indicates that it contains O2/N2 but an all Yellow cylinder would imply that it contains a Toxic and/or Corrosive Gas.
However, our understanding of the regulations is that only labelling is a legal requirement, therefore, there is no need to impose colours on amateur clients. However, there are numerous standards and guidance notes that both colours (EN 1089-3) and labels (EN ISO 7225) should be applied, therefore, it would be wise for those at work to both label and colour their cylinders.
ASSET recommends that all cylinders should be both coloured and labelled.
Please not that due to variations in national legislation, in individual EU Countries, the requirement may vary. If in doubt, cylinders should be both labelled and coloured

Q. Where can I find guidance, information and templates for cylinder labels?

A. ASSET can provide artwork for Air, O2, Mixed Gasses, O2 Cleaning and Next Test Due. The artwork takes into account HSE guidance 2005 on diving cylinder labels and complies with EN ISO 7225:2011.

The HSE advice reduces the number required for a possible 6 to 3 labels i.e. Breathing Air, Oxygen and one label for nitrox/heliox/trimix)

The artwork comes in JPEG format (others can be provided)

The artwork is free of charge to ASSET members. For none members, the price is £25 per label or £80.00 for the set.


Q. How many turns can be allowed on a Not Go Gauge when inspecting cylinder neck and valve stem threads.

A. The "by the book" answer is that there should be no turns allowed on a Not Go gauge (if you think about it, that's why it's called a Not Go gauge!). However, in many industries, particularly where maintenance activities are concerned, it is common to allow something for reasonable wear and tear.

In the past, (mid 1980’s) the general advice given (and widely accepted) in the UK concerned only the G3/4" thread. That advice was that up to 4 turns on the Not Go gauge could be allowed in the cylinder neck thread, providing that the cylinder thread had an adequate number of full threads and the Not Go gauge does not go on the valve thread.

However, over the past 20 years or so, M25, G5/8" and 3/4" NPSM threads have become widely used additionally ASSET's membership has become Worldwide, therefore, it has been necessary to revise and rationalise this advice.

To keep matters simple, we believe a reasonable rule of thumb to be as follows: Providing the technician is satisfied that the threads on both male and female threads are physically sound and of full form and that the male threads have been gauged and the Not Go gauge does not go then 1 (one) turn on the Not Go gauge might be allowed in the female thread for every four good turns engaged. In effect this means approx 1T on a 200 bar Din outlet, 2T an M25 and 3T on a G3/4" and so on.

For 3/4 NPSM threads, there is further guidance in CGA 6.1 2006 clause 5.9 Threads and Valving as follows:

Cylinder threads should be examined whenever the valve is removed from the cylinder. Cylinders have a specified number of full threads of proper form as required in the applicable thread standards. Cylinders shall be rejected if the required number of effective threads is materially reduced so that a gas tight seal cannot be obtained by reasonable valving methods. Thread defects include threads that are galled, worn, corroded, broken, cracked, nicked and double threaded (by forcing an incorrect valve into the threads) should be rejected.

This guidance should be applied with caution and is at the discretion of the individual technician who must take into account the circumstances as they present themselves.

Q. Is there any British Standard that confirms engineering practice of allowing 2 threads on a 25x2 no go plug thread gauge (4 threads on G3/4)
The only reference I can find is the notes taken during our course and CP2 8.15 note attached to point 2.
During my days as a turner any threads manufactured where the no go gauge entered at all were scrapped. Just want to get things straight in my mind before I start scrapping things I should have passed :-)

A. There is no such standard, however, see also the answer above.

Q. I have been asked to inspect and test a number of cylinders for some guys that have recently bought up a dive centre here in Cyprus. The majority are Luxfer and Catalina Aluminium, (several failures already for excessive pitting)
I also have 2 15L Heiser steels, with a G3/4" neck thread, however there is no O-ring groove on either cylinder.  I don't want to try and hydro them as I'm sure the O-ring will blow out as there is nowhere for it to sit and seal.  The word ARIA appears at the 200/300 working and test pressure figures, I've seen the same on Faber's for the European market.
I wondered if you could provide me with some advice, it appears that Heiser are now part of an American company called Worthington, but nothing about scuba cylinders appears on their website.

A. These cylinders are manufactured to an Italian spec (the clue is Aria which means Air in Italian!), they are not legal in the UK, but who knows in Cyprus?
These cylinder types were manufactured to mate up to a curiously Italian valve arrangement where the O-ring seal is in the flange of the valve! You would need a compatible valve to use them (and a suitable adaptor to test them). They won't seal against a conventional (EN 144-1) valve because there is nowhere for the O ring to go!
You may not be able to get replacement valves because, like the rest of Europe the Italians have moved over to EN Standards.
 By the way, the Catalina cylinders will most likely be American DOT standard containing 3/4" NPSM neck threads; if so do not put G3/4" (3/4" BSP-F) valves in them!

Q. I have 20 cylinders to test made up of 10-12-15 ltr. On 14 of the cylinders, the go gauge won’t go past the neck end of the thread it comes to a dead end. It passes through the neck on the others, which are the same make. I read my notes to say that as long as the gauge goes are far as the valve thread its passable?? Am I right in thinking this or should I fail them do you think.

A. You are right, as long as you're satisfied the neck area is sound, gauges satisfactorily and you have sufficient good threads in the cylinder neck to accommodate the length of the valve stem they should be ok.


Q. We have received some inquiries about the correct order of inspection or testing stamp marking on cylinders.

 A. BS EN ISO 13769:2006 gives the order of stamping as # YY/MM - Where # is the inspector's mark and the year and month is separated by a forward slash. 
Although not required by the standard, in order to prevent confusion over the reversal of the month and year after 2002 (previous common British practice was MM#YY), we continue to recommend that until 2013 that the year is stamped in full, i.e. # YYYY/MM.
There is an anomaly in the standards. None of them make provision to differentiate between a visual inspection only and a full inspection and test. Prior to these EN and ISO Standards, it was common practice in the UK to stamp the letter “V” to indicate a visual inspection only. The HSE have asked us to continue to this practice.

Q. I hydro tested four cylinders today and three of them failed with readings of 10, 11, and 12%, I was concerned at this and so retested them only to get near enough the same results, I then tested one of my new ones and the percentage was 0%, so at least I know that what I was doing was correct and that the hydro itself seems to be working ok.

The only difference was that when I was testing the failed cylinders the water in the burette was constantly creeping up but the pressure gauge seems to be holding. Could you give me a reason for this and whether it’s usual to get three cylinders fail like these three did.

A. Firstly, a creeping burette will invalidate the test. The cause must be found and corrected then the cylinders must be re-tested.

A creeping burette, with no movement of the pressure gauge, is suspicious. Either the water inlet valve is leaking into the rig or the pressure gauge is dropping but, so little, you’re not noticing it.

Secondly, if the cylinders are genuinely expanding a drop in the pressure would be expected, but this may not be by very much.

Thirdly, it's unusual but not impossible to have three fail on the trot.

I recommend that you choose one of the “failed” ones and retest it. Make sure the test system is absolutely leak tight. If it then fails, it is a dodgy cylinder. If it passes, you must re-test the other two also.

Q. Can you give me further advice on how to treat an Aluminium Cylinder that came in with dents/gouge on the outside, the size of :- The Largest being 2mm Wide .75 mm Deep,  5mm Long. There are others and these are two to three inches away from each other, about 4 or 5. These are smaller about 3 mm long 2.5 mm in width and .75 mm deep.

Because they are separate from each other and I calculate that the minimum body thickness is intact according to Standard requirements and the Drawing the Manufacturer emailed me and because it’s not corrosion am I right in understanding that as long as the Minimum wall thickness allowed is intact the cylinder is fit for purpose and can be returned to service.

A. There are three things to consider.

  1. The physical dimensions of the defect, these are clearly set out in EN 1802. (There is a précis of these in the both the ASSET DITC and CTC Pt 1Handbooks).
  1. The age and cumulative condition of the cylinder


  1. The conditions of service

On the basis of individual measurement, if your calculations show that each defect is within limits and you have at least minimum wall thickness, you are correct in saying that the cylinder (from what I understand from your description) can be returned to service.

Before you do, you should consider if the defects are very close or line up in an almost straight line which may cause some cumulative weakness. Then consider the conditions of service, is it harsh or arduous? Finally do you believe that the cylinder is safe "for another period of use"?

If you're satisfied, return it to service, if not you should scrap it.

Q. I'd like to ask about a cylinder that I failed. It was one of a batch that a regular customer (dive shop) gave to me - Faber, serial No 27488, Manufacture's date 27-1-76.
No specification. An 8 thread G3/4 reserve Valve held open with a piece of wire, coated inside with red lead paint, cracking, with rust bubbling the red lead.
I've cut the neck off of it, because it failed several inspections.
 I've copied the worksheet, and the failure sheet, and I just want your backing, before I tell the customer the bad news.

 A. The "red lead" inside the cylinder isn't. It’s probably a factory applied epoxy coating, intended to provide protection. As you can see, it doesn't! This process was used, most notably by Rothmions", until the 80's when they saw sense and stopped applying such coatings.
Your decision to scrap is probably the correct one because, having done a few, that coating can be difficult if not impossible to remove. The condition you describe indicates moisture penetration and corrosion underneath the coating, which must be removed to allow proper inspection of the surface condition.
The difficulty and cost of refurbishment is probably more than the cost of replacement.
If the working pressure is 200bar or higher, there should be an 11 thread G3/4 valve in it.

IDEST bulletin on cylinder valve maintenance
Q. In the IDEST Bulletin for January they have made recommendations on the frequency of cylinder valve servicing:

“DfT and UKAS have expressed concern that some technicians fully strip and service the cylinder valve at every inspection while others appear to do so only if it appears necessary.  We have discussed this matter often and at the two members' symposia held at Luxfer, there was a unanimous vote for all to undertake a full service of the cylinder valve at each inspection/test.  So, from now on, when you have you cylinder tested, the valve will need to be serviced at the same time.  This will add on a cost, but what price safety”.

A. I question the statement "what price safety"; a valve that is not in need of refurbishment is no safer after it has been refurbished!
Whilst IDEST test stations may have "voted" for this, it is not in line with the Standard. I paraphrase: EN14189 requires that the valve be cleaned and inspected (externally) and the airways inspected. If necessary the valve should be refurbished.
 Additionally, the manufacturer may state a maximum period after which time the valve should be refurbished. This may be less than the 2.5 years between inspections.

The whole purpose of this standard is to allow the technician discretion and to be able to discriminate between valves which have had heavy or light use or those valves which have recently been replaced and do not need refurbishment. Therefore, allowing the technician, based upon his findings to act accordingly. Putting an arbitrary "must service at every inspection" removes the technician’s discretion.

 However, EN 14189 requires that, after refurbishment, the valve must be stamped with the date of refurbishment. This raises the problem of stamping a chrome plated scuba valve, which has a relatively small surface area, every 2.5 years. This would quickly cover the surface in stamp marks.

An agreement has been made with HSE that testers of Scuba or BA valves need not stamp the valve so long as the valve is refurbished at every inspection or test.

For large none chromed valves in industrial gas cylinders :

    • Comply with the requirements of EN14189.
    • Check and comply with the manufacturer's requirements.
    • If in doubt refurbish the valve
    • Stamp the valve to show the date of refurbishment

Q.I have received a small cylinder that has half of the ID numbers stamped right on the shoulder so half of them are missing and there are a few suspicious marks on the top. Although I have not inspected inside yet, do you think this would be a failure?  Picture sent.

A.I see what you mean, this is badly stamped in manufacture and should have been rejected by the shop that supplied them.

You will recall that the rejection limits call for cylinders whose makings
are illegible to be scrapped.

It’s obviously manufactured to BS 5045/1/CM/S, however, If you can't make out the other info that you need to test it, then you have no other choice but to fail it.

However, if you genuinely can't make out the all the technical info (I can't
make much out from the photos), this needs taking up with the supplier and the manufacturer, if this is the first test, the owner should ask for
replacements and if they get no joy they should contact  trading standards.

Q. I have been told that emergency inflation and lift-bag cylinders do not need testing because they are “self filled”. Is this true?

 A. This is one of those diving myths that is completely untrue. All such pressure vessels must be tested. The inspection and testing periods are the same as any other Scuba cylinder.

Q. What are the testing periods for gas cylinders?

A. Cylinders used for permanent gases – a visual inspection and hydraulic test every10 years.
Scuba Cylinders – a visual inspection every 2.5 years with a hydraulic test every five years.
BA Cylinders – a visual inspection and hydraulic test every five years.
For other types refer to EN 1802 and EN 1968

Q. I’ve been told by other air gunners that my cylinder that I use to charge my air rifle only needs testing every five years but my local dive shop tells me that it must be treated as a Scuba cylinder and be tested every 2.5 years. Who is right?

 A. The deciding factor is not what the cylinder is used for but the type of valve that is fitted. The HSE have confirmed the following:
If the valve fitted is normally used with scuba equipment then a visual inspection is required every 2.5 years with a hydraulic test every 5 years.
If the valve fitted is designed specifically for charging air weapons i.e. has a built in gauge and bleed screw will need a visual inspection and hydraulic test  every 5 years.

I was testing six 8 litre cylinders for a customer who used to service fire extinguishers. Four of them had what I believe to be suspicious marks at the bottom of the cylinder, which to me look like cracks. I determined that I would fail these. I filled in paperwork and informed another inspector who said he would take a look. He said he thought it was tool markings from the manufacturer and he then went ahead and passed all 4 of the cylinders, because “the proof test confirmed to him that the cylinders were safe”.

From what I have learnt from your course, going by the rejection criterion, for suspicious marks “reject all if investigation does not confirm acceptable cause”. I strongly believe that cylinder should not been returned to service.  But because my colleague dismissed my decision I’m concerned that I will be overruled again in the future.
I have taken copies of documents that I used to fail the cylinders, for my record.  

Q1. Was I correct in my understanding of the rejection criteria to have reasonable doubt to fail these cylinders?

Q2. Does my colleague have the right to dismiss my decision? 

You don’t say what your colleague’s qualifications are. Is he qualified to act as a competent or approved person?

A1. Firstly, a proof test cannot be used to override the result of a visual inspection. There are numerous factors that might cause a cylinder to fail a visual inspection that a hydraulic test would not detect. Therefore in this action, your colleague is mistaken or misinformed.

A2. Secondly, you are correct in your understanding that if you have detected a “suspicious mark” with no acceptable cause, you are right to reject the cylinder.

A3. Ultimately, the question is: are these actually suspicious marks or are they something to do with the manufacturing process? If you are certain of your diagnosis, stick to it.

A4. If you are signing the test form and certificate as the competent person you are responsible for that decision and therefore your colleague has no right to overrule your decision. If he is adamant that he is correct, have him take responsibility by signing the work sheets and certificates

Q. Can you provide some guidance on testing standards for “J Bottle” used for a storage bank?

A. The standards for testing these are exactly the same - EN 1802 or EN 1968. The procedures are the same as you learned in the ASSET CTC course and are in the course manual.

The only real practical issue is size and therefore handling and drying will need some adaptation. Unless your insurance company says otherwise, "bank" cylinders are treated like BA cylinders (because they are filled from a compressor) and are usually tested every 5 years.

The most practical method for testing such larger cylinders is the "Proof Method". By disconnecting the hose from the jacket tester, extending it and connecting directly to the cylinder to be tested you have created a proof test rig. There is a proof test procedure in the current CTC course.


Q. I am having great trouble finding torque settings on the drawings that SITA provided. Do valves in steel cylinders get torqued to 140Nm and in Aluminium to 130 Nm or are they different? Also had some tools made now and wondered if you only used the cylindrical tool with the half inch hole for torqueing up?

A. You won't find torque values in cylinder drawings.

EN 1802 and EN 1968 refer the technician to EN 13341 for torque values for current gas cylinder valve threads. A list of suitable torque values can be found in both the ASSET DITC and CTC Pt 1 Manuals.


Q. I am now testing BA cylinders and what I need is more info on HOT cylinders i.e. drawings if pos they seem to be made by IWKA I also have some that are stamped on the shoulder of the cylinder as opposed to the brass collar. Your manual says do not stamp the shoulder. Isthere any further information on this?

A. IWKA is no longer trading. Colleagues in the trade may be able to assist. We have accumulated some drawings for older cylinders which may help.

HOT cylinders date from the 60's and 70's. The HOT Standard 1966 Amendment is clear about the need for an overall zinc coating 0.005" thick if used underwater.

I enquired some years ago about the issue of stamping on the shoulder.

I was advised by the technical dept of Chesterfield Tube Company (CTCO) not to stamp the shoulder, unless there is a clear indication that the manufacturer had stamped there. Additionally, if the cylinder has been stamped on the shoulder but there are no manufacturer’s marks there, the cylinder should be withdrawn from service.

In addition, there's the obvious common sense issue - "why would a manufacturer fit a neck ring to take the stamp marking, if the metal is thick enough to stamp the shoulder"?

Part of the problem is that testing standards do not highlight the unique service requirements that are part of the original design specification which may lead the uninformed tester to miss this requirement.

Many testers will not have a copy of HOT to refer to.

Where HOT cylinders are concerned

If a HOT has a neck ring fitted, the cylinder will need a Zinc coating, if it is to be used underwater.
The Zinc coating must be 0.005" overall and be checked instrumentally.
Do not stamp an HOT on the shoulder unless the manufacturer also did.
If it’s been stamped on the shoulder by anyone other than the manufacturer and there are no original manufacturer's marks on the shoulder, fail it as if it were stamped on the parallel.
Do not stamp through the Zinc coating.
If it's Zinc coated, there's only one place you can stamp it that’s on the neck ring!


Q. Where the best place is to buy the following:

Endoscope or Boroscope
Ultrasonic thickness gauge
The gauge for measuring the thickness of zinc?
Biox and the detergent Stewart uses? (could you tell me the name of the detergent please)
Last but not least any advice as to where should get Master Gauge calibrated also thread gauges (calibration and buying) and torque wrench calibrated?

A. It's always worthwhile doing an eBay search
We’ve seen a suitable U/S thickness gauge is on eBay type TM8811 for $130 + £19 p&p
For a boroscope try www.fibrescope.net about 400 $Canadian also a choice on eBay. Also digital scopes are getting cheaper and more usable – make sure it has a 45 degree mirror and can focus from 1cm to infinity.

Coating thickness gauge - only required for the old HOT standard cylinders used in the UK. Only tackle HOT if you’re sure it will pay for the cost of thickness gauge otherwise it’s cheaper to refuse them. There was an Elcometer 355T on Ebay for £100 (a good make)

I get all my gauges etc calibrated at same place in Southport, but you must be able to find somewhere that does them nearer to home. Try a search for “Metrology”, “Calibration Services”, “Instrumentation” and “pressure gauges” in Yell.com

For a list of suppliers click on Workshops, then click on Contacts.


Q. I've been doing a bit of servicing and am having a bit of a problem with 02 cleaning of cylinders,
I'm filling them with Biox leaving them over night washing them through in the morning but I'm getting a black residue around the top of the neck.  Can you advise? Thanks.

A. The residue is probably caused by the Biox foaming and therefore including air at the top of the neck.

You can prove this by filling it, plugging the neck with a valve then inverting the cylinder. The usual fix is to fill it absolutely full then fit a valve and close it. A small amount of gas and therefore pressure is produced, so open the valve very slowly to release it before removing the valve.

Note: chemical cleaning agents, including Biox, can react with the steel to produce a dark oxide coating on the steel. Providing the cylinder is thoroughly rinsed after cleaning this darkening is ok.

Q.I need some advice please on the drying of the cylinders after hydro and shot blasting. I seem to have 50% of my cylinders flash rust when drying. I have a leister air dryer and this is on a setup very much the same as yours in the work shop.

I read that drying too quickly is one cause, so I tried a lower heat (I use
around 150 deg's temp) but this still didn’t work. I've left the cylinders to
drain longer before starting the drying. I’ve tried blowing compressed air after a kettle of hot water. I've steamed and purged but nothing seems to work. So any advice would be welcomed.

A. One of the main causes of this phenomenon is the quality of rinse water; a second is the speed of drying.

If the local water is “hard” or has high mineral or metallic content, flash rust may occur. The best cure is to use de-ionised or distilled water for the rinse.

You have the speed of drying reversed. The faster the cylinder is dried the less likely you will get “flash rust”. Steaming followed by blowing with air is usually the fastest method. Put de-ionised water in the steamer.

In America you can buy an anti rust wash for cylinders called compound “O”. I believe it contains Sodium Chlorite (not chlorate). However, when I enquired (some time ago) about a similar product in the UK the supplier could not tell me that it was ok to use in breathing cylinders, so I didn't try it.

Note: Light “flash rust” is not normally a problem in air cylinders but is unacceptable in O2 and Nitrox cylinders

Q. I have been trying to dry a cylinder after a hydro test and keep getting rust stains inside it when originally it was in pristine condition. I have steamed the inside for 8 minutes and then blown dry with an air gun both lying down and vertically. The rust stains still appear. Can you tell me why please and if I am doing anything wrong. If there is another way I would appreciate your advice.
I have set up a steam cleaning method as yours worked perfectly on the course, thanks again in advance.

See the above answer.

Q. I have a question that hopefully Stewart can help me with. Most dive centres and filling stations will not fill a Nitrox cylinder if the date of service/O2 cleaning is more than a year old. I know from what Stewart said on the course there is no set government regulation stating this, however it is still very good practice.
I am not at the moment working for a company that has an approved workshop. However, as both an ASSET trained Nitrox technician and cylinder testing technician, can I set up a clean area and oxygen clean cylinders and mark them as Nitrox clean, without stamping them as have been visually or hydraulically tested?

 A. Technically, there is no such thing as an "O2 Cleaning Period". If something is O2 clean, no matter how long since it was last cleaned, it doesn't need cleaning. If there was such a period, the gas companies would have to regularly retrieve thousands of cylinders from the field just to clean them thus causing havoc.

However, in scuba diving, we do not have the same control over gas fills and usage of cylinders as the gas industry and therefore, although not a statutory requirement, more regular cleaning, of scuba cylinders, is a good (and recommended) practice.

The one year period (which we and HSE originally recommended) came from America (where scuba cylinders must be annually inspected) in Nitrox diving manuals. This period was simply adopted, without questioning its validity, by those teaching Nitrox in the UK.

Had Nitrox diving been invented in the UK (using the same logic used in the USA) the cleaning period in accordance with BS 5430 (now obsolete) would have been every two years!

Since 2002, when EN 1802 and EN 1968 came in, the "adopted" USA one year cleaning period became unworkable.

Therefore, the HSE provided some guidance which stated that the O2 cleaning period should be extended from twelve to fifteen months, in order to fit evenly into the current testing period.

Note that this is the maximum recommended period. If contamination is suspected or detected, the cylinder should be cleaned regardless of how recently cleaned.

Q. What kind of O2 cleaning do you recommend for cylinders? Everybody seems to have a different opinion.

The reason why there are so many apparent methods is that most people don't understand that the standard for O2 cleanliness is about the inspection method not the cleaning method. When you attend an ASSET Nitrox Technician and Blender’s course, you will learn how to carry out an O2 inspection correctly.

The technique used for O2 cleaning depends entirely on the item to be cleaned. For example the method for a cylinder is different than for a regulator. These techniques are taught on the ASSET Nitrox Technician and Blender’s course.

With regard to cleaning products, the key is effectiveness and efficiency. Household cleaning products are definitely not suitable. There are bespoke O2 cleaning products on the market like Biox. If not managed properly these can work out expensive, often resulting in the use of cheaper and less effective products.

ASSET Courses are designed to teach diving professionals how to carry out all the required tasks to a high standard but also economically. I highly recommend you attend the full suite of ASSET courses. Our ex students will tell you that they pay for the course fees with the savings they make from what they learn on our courses.


Q. Has the situation changed regarding the testing (or rather not testing) DOT cylinders?

A. As far as I'm aware there has been no change in the legality of DOT SCUBA Cylinders in the UK.
The general rule is simple: if the cylinder is not made to a suitable standard e.g., BS, EN, CE, Epsilon or ISO or, in the UK, is on the obsolete “approved list”, they are illegal to fill.
The UK obsolete approved list can be downloaded at: www.hse.gov.uk/cdg/stdobso.htm


Q. Must I always use an ultra-sonic cleaner to clean regulator components?

 A. There is no general requirement to use an ultra-sonic cleaner. However, an ultra-sonic cleaner is quicker and more effective than manual methods.

Additionally, it is difficult to achieve “Oxygen cleanliness” without one.

Q. I’ve been speaking to a scuba technician who has done the ASSET course as well as most of the manufacturer service courses. This guy is adamant that it is a legal requirement for a technician to do the manufacturer service course to be able to service that make of regulator.

My understanding, and as discussed with you at the course, of the legal requirement is that a trained and competent technician can service regulators and that the manufacturers service course is not a legal requirement.

Can you confirm this for me?

Additionally, the technician called up a manufacturer to ask them where would an ASSET technician stand, if an accident happen as a result of regulator failure post service by a technician who had not done the Scubapro servicing course. They said that the technician would “not have a leg to stand on legally”.

Do you know if this is true?

A1. I don't know where our member got his information but there is no legal requirement, in the UK, to attend manufacturers' courses.
A2. With regard to this manufacturer's comments; if not completely wrong, they are simplistic and misleading. The law require that the technician is “competent”. Although, in the overall scheme of things, attendance on manufacturers’ course is desirable, it doesn’t automatically confer competence.
A generally accepted definition of competence is “trained and experienced”. The training part is not defined in law and would, of course need to be adequate but it does not automatically follow that a manufacturer’s course is adequate and, more importantly, sufficient , just because the manufacturer decided on its contents.
It is always possible to be convicted, by a court, for an error that led to an injury or fatality, despite having attended a manufacturer’s course.
In order to establish the level of competence, a prosecutor, might ask if the individual had attended the manufacturer’s course. However, competence does not depend upon this and therefore, adequate training might be demonstrated by another route, as in other industries, such as ASSET qualifications or an employer’s in house training scheme.
It could be argued that, compared with a manufacturer’s course (the majority of which last less than 8 hours) by attending a 10 day ASSET Technician’s course and passing the required exams to become ASSET certified, the technician has demonstrated a responsible attitude to the need for training and their desire to expand their experience and competence far beyond what the average manufacturer’s course delivers.
The experience component of competence is more problematic, especially for the self employed or the individual working alone. The HSE often cite 5 years as being reasonable experience. This is a real problem in an industry where the majority of newly qualified technicians have no opportunity to gain experience working alongside an experienced technician. 
There is no easy answer to the problem of experience other than to say, in the technician’s first few years he must be careful, vigilant, work by the book and double check everything.
Regardless of training and experience, it is essential that the technician has access to manufacturer’s workshop manuals and genuine spare parts for the equipment in question. It is also essential that the manufacturer’s settings and set-up procedures are followed.
Manufacturers or their distributors often operate a closed shop, where training information and components are concerned. Members have reported that they have been told “they are breaking the law” or “what they are doing is illegal” and that “without completing the manufacturer’s course, warrantees are void”.  In the first two instances they are wrong and in the latter they could find themselves in breach of EU competition law.
There is already a precedent - in the EU, motor manufacturers have been forced to provide the necessary technical information so that third party workshops can offer servicing to motorists without compromising manufacturer’s warrantees.
I hope this is of assistance. If you have any further concerns, you should consult your legal representative for a definitive legal opinion.


Q.I need some advice on air purity.

Having successfully tested for oil (no trace), CO (no trace) & CO2 (within
limits), I’ve got issues with the content of water vapour.

I’m using an Air-Care Breathing Purity Kit which utilises Kitigawa detection tubes. I have taken numerous water vapour tests with differing results each time. Is there a method that I should be adopting, or is the current high air humidity playing a major role in the results?

The latest tests are from a cylinder that was filled to about 130 bar in an
air conditioned room with surrounding humidity of 34%. I replaced the self packed filter with one supplied from Coltri to enable me to eliminate the possibility of incorrect packing on my part.
I conducted 2 tests from this fill, the first was about 1 hour after filling; this was conducted outside of the air conditioned room and gave a reading of around 110mg/m3. Several hours later I conducted a further test on this fill, this time in the air conditioned room with lower ambient humidity, the reading for this was then 70 mg/m3.

Is there a special procedure for testing water vapour as I have followed
both the instructions for the test kit & those instructions supplied with
the kitigawa detection tubes (only difference being the length of purge
before connecting test tube, 30 seconds as opposed to 10 minutes). Could it possibly be a fault with the compressor, if so what may this be.

I really appreciate the time you take to reply.

A. Your test method is sound and assuming your test unit is correctly calibrated the results you are receiving appear to be valid. Even taking into account the fact that colourimetric tubes can vary in accuracy by as much as 20% these readings are high.
Having fitted a new cartridge to the compressor, you should initially get dry air, even if there's something wrong with the separators or auto dumps that is preventing removal of condensate.
I would be inclined to press the supplier hard on this issue because it just shouldn't happen.
If you get the run around, you can get an independent laboratory test from Aquatron in Glasgow. You will then be able to go to Trading Standards to get something done.

Q. With an HP compressor, used for diving quality air, what are the requirements for testing the filter tower assembly?  I would assume that it would follow the requirements for a land based, fixed, pressure vessel, but am not sure.
Similarly, is there any statutory requirement to service/test the interstage relief valves or the filter tower relief valve?
Your guidance would be appreciated.

A. My understanding is: Test the filter housing every 5 years or replace it, depending on manufacturer’s recommendation. For example, Coltri require the replacement of their filter housing after X thousand hours.
There is no specific statutory requirement to service or test safety valves, however, the PSSR Regulations require that the compressor is maintained in a safe condition and there is a “written scheme of examination”. Follow the manufacturer’s recommendations for these, as you should for any other item.

Q. Could I ask Stewart’s advice on the installation of our compressor. Our premises consist of one room, 450 sq ft in size, with extremely high eaves. As the compressor is to be located in the same room we have had to build an enclosure around the compressor to dampen the noise levels.
I have followed the advice from the manual and ensured that the compressor is situated 1metre from the sides & back of the room to ensure ventilation. The room measures approx 11ft x 8ft with a ceiling height of approx 8ft. Even though the compressor has enough room around all sides, I’m a little concerned that the heat generated from the compressor in such a confined space would cause problems with the running and life expectancy of the compressor. The other issue I have is the air intake, would it be feasible to put an extension to the existing air intake & out through the ceiling (approx 8ft) into the open shop.
I would really appreciate your help and advice.

 A. You can't simply enclose a compressor with the recommended distance all round without ensuring adequate air flow into and out of the space. In other words, if you enclose the compressor, you'll need to put louvers, preferably in the outside wall to ensure a flow of fresh cooling air in and exhaust the hot air produced out. If you fail to do this, the compressor will overheat. Premature wear or even catastrophic failure could result.
These things don't happen immediately, all will seem to be well, until one day..!

With regard to the air intake, any significant length of pipe run should be of larger bore than the connector to minimise air resistance. Check your manual or with your compressor supplier/manufacturer for the maximum length at standard bore. 

Restriction of the inlet airflow can cause significant overheating in the same way that a blocked inlet filter does.

 Q2. Many thanks for your advice. Would installing air conditioning in the room solve the problem, for both cooling the compressor & giving an adequate fresh air supply to the air intake?

A2. I can't say. It depends upon the ambient temperature, the volume of the space the heat output from the compressor and the power of the air conditioner. Fresh air is usually cheapest and best. Even if I had the data, I'd need a refrigeration engineer to work out the size of the air con.

Besides one day the air con will break down or run out of gas without you noticing, and then..!

PS An air con won't provide fresh air to the intake, it only cools the air. The air intake should be piped to outside.


Q. I have a question to ask about fitting of neck seals as per the system in your manual. I have the rings but it says two sided tape to hold the suit and neck seal in place. The question is: do I use carpet tape or is it too strong and is there something else that is more fitting for the job and when taking the tape off is there any simple tricks of the trade. Apart from this I have been very pleased with my new job and the foundation you gave me with which to go forward.

A. Carpet tape will be too strong to hold the seal to the ring, but may be good to hold the disc to the suit. For the neck seal use ordinary office quality double sided tape. I'm glad the job is going well and your time with us has provided you with valuable skills.

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