Home Scuba Diving Gear Proposed changes to UK cylinder testing

Proposed changes to UK cylinder testing



The UK recreational and technical diving industry is continuing to lobby against a forced change to a proposed ISO cylinder testing standard. Rosemary Lunn reports on the situation

Historically, the UK cylinder testing regime for scuba cylinders used to be every two years (visual) and every four years (hydraulic). The cylinder is also visually tested when it is hydraulically tested.

This changed in September 2002, when IDEST (Inspectorate for Diving Equipment Servicing and Testing) was one of the parties that advocated that the hydraulic test period should be increased to a five-year period in the UK. Therefore, the visual inspection period was increased to two-and-a-half years. In other words, the test cycle time was extended!

Now the UK is under pressure to amend this test cycle and bring in an annual cylinder visual test. While we do not know what the new test specifications are going to be, it could be a retrograde step, and may not be as rigorous as the current 30-month British visual.

What is equally maddening to the UK diving industry is that there is no evidence that this change is necessary, nor that it will proportionally increase safety. In fact, many diving professionals and agencies worry that it will make diving less safe because a certain amount of cylinder filling will go ‘underground’ as divers look to save money on testing.

There is already anecdotal evidence on social media that divers will buy a personal compressor to avoid cylinder testing. This is a typical comment:

Buy your own compressor. £1,500 outlay but no more testing! (You can do your own visual if you want). I bought mine six years ago, perfect air fills every time, 240 bar, no half fills, no dodgy air, or waiting for dive shops to open, and I average 50p per fill costs, including twice yearly servicing the compressor. It’s a no-brainer for me.” 

cylinder testing 1

The fear is that this new annual standard will put the divers at risk because there will be less adherence to the current inspection and testing regime. Divers will simply not get their cylinders tested. No one wants to be around a cylinder when it fails, and it is possible that when a cylinder is not inspected for a number of years that it will fail at some point, be it at a dive site, on a dive boat, or in a car when it is being transported.

The proposed ISO annual test is an international standard and it is being applied to every cylinder across the board – from 0.5-litre to 120-litre – in every industry, from aviation and brewing through to cryogenics and diving. This new standard is being pushed by America and Australia – two countries where quite a lot of diving is done on aluminium diving cylinders, where there has been issues with the cylinder necks cracking.

So, let’s compare the UK IDEST visual test process against the USA process.


  • The cylinder is logged in on a job sheet.
  • The boot and any stickers on the cylinder are removed.
  • The cylinder is externally assessed for damage and corrosion.
  • The cylinder is checked to ensure it is empty. If it is not, any gas is released.
  • The valve is removed using a special jig to ensure that it is not damaged.
  • The stem threads (the part that is screwed into the cylinder) and the outlet threads (where you screw your DIN regulator into the valve) are cleaned.
  • Once cleaned, both the stem and the outlet threads are checked with a GO gauge. If the GO gauge does not go all the way, then the threads are inspected to find out why this could not happen.
  • The stem and outlet threads are then checked with a NOT GO gauge. This should not go on more than two turns maximum on the threads. If it does, there is a fault with the threads and they are duly inspected.
  • In the case that the valve passes the GO / NOT GO gauge test, it is then dismantled and put into an ultrasonic cleaner to clean all the parts.
  • The cylinder is placed on a bench and internally inspected using either a drop light or a Boroscope. If a drop light is used, then a dentist’s mirror is utilised to check the inside of the shoulder for damage, corrosion, or anything abnormal.
  • The valve is washed in fresh water, dried and reassembled with new O-rings and white Teflon washers.
  • The valve is then screwed into the cylinder and made ‘hand tight’. It is then torqued to the correct tension.
  • The cylinder is stamped with the IDEST centre’s unique stamp, including whether it has been visually or hydro-statically serviced. It is stickered to show when it is next due for a service.

In the USA, cylinders are visually inspected only. While the threads are closely looked at using a magnification device, they are not physically checked with GO / NOT GO gauges, nor is the valve always serviced at this time. It may be serviced. It may not be serviced. Unlike the UK, there are no set standards for cylinder inspection, other than a hydrostatic test must be conducted every five years.

cylinder testing 2

In other words, in a typical USA visual service, the valve is whipped off, a technician takes a look and puts the valve back in. It is a basic inspection and does not remotely compare with the current, safer IDEST visual inspection.

In February, a BSI (British Standards Institute) meeting was held in Pretoria, South Africa, to deal with 130 amendments to standards. Only 58 standards were covered, and a follow-up meeting is scheduled for late-April 2017.

The British Sub Aqua Club (BSAC) sponsored Gavin Anthony, a forensic scientist specialising in the testing of diving equipment, to attend this meeting. Gavin Anthony was the only scuba specialist in the room. He advocated against this standard, asking for the evidence that shows annual visual testing will make diving safer. There has been a lot of talk, but no solid evidence has been forthcoming.

The UK voted against the standard change, but was outvoted. However, the final content of the standard is not yet fixed and IDEST is still pursuing a proposed amendment to the recommended interval for internal visual inspections.

In the meantime, IDEST has not seen any evidence that this change is necessary, nor that it would proportionately increase safety and so, with the support of SITA and the UK recreational and technical diving industry, is against an increase in the frequency of inspection for diving cylinders.

IDEST has got data proving that the 30-month visual inspection is satisfactory. They have been monitoring why cylinders fail. Their data confirms that on a small percentage of cylinders fail because of internal and external rusting. However, 75 percent of failures are caused by thread issues. Given that 75 percent of failures are due to thread wear / damage, what is the logic of increasing the frequency of removal and refitting?

Since 2012, thousands of cylinders have been tested in the UK. In that time, there have been approximately six cylinder accidents. One cylinder exploded. It had suffered massive corrosion and had not been tested for six years.

The reason that the UK recreational and technical diving industry has been safe up until now is that thanks to IDEST, we have a thorough, periodic internal inspection regime that encompasses thread gauging.

For instance, it picks up on the issue of mismatched valves and cylinders. This occurs when an untrained person screws together a valve with one size thread (say M25) into cylinder with another size thread (say G3/4). It is possible that when the cylinder is filled that the valve may not fully come out and air leaks from the cylinder. Unfortunately, last year, a member of staff in a dive shop in Europe was killed when a valve blew out of the cylinder he was filling. It hit him in the face, and he died three hours later.

The use of GO and NOT GO gauges also ensures that where cylinders and valves fail the thread gauge tests, they are taken off the market and destroyed. If the use of thread gauges is not part of a visual inspection, it will cause issues.

cylinder testing 3


The adoption of the ISO standard is automatically undertaken by the countries who signed up to the Vienna Agreement in 1991, and this includes the UK. Consequently, this would apply whether or not the UK is in or out of the EU because the decision to comply with the Vienna Agreement is one made at governmental ministerial level.

In the meantime, the whole of the UK’s recreational and technical diving agencies, along with SITA and IDEST, continue to advocate on behalf of UK divers and explore alternatives to the proposed testing changes. One possible route is via a risk assessment.

Not all pressured cylinders are treated the same way in the USA. Diving cylinders are classed as ‘sport and recreation’. They are not classed as ‘commercial cylinders’. Therefore, BSAC has been discussing the idea of introducing a risk assessment alternative for domestic cylinder use with the HSE. However, divers may have to prepare for an increase in cylinder inspection frequency if this is not successful.

It is currently anticipated that, if implemented, the cylinder testing changes could come in as early as October 2017.


IDEST – A potted history

IDEST was founded in 1985 by Mike Todd. Before this time (in the UK), there was no standard for servicing cylinders and regulators. Divers, therefore, had no guarantee as to the technician’s skill or expertise, nor to what level the equipment was serviced to. For instance, one technician could visually test a cylinder by taking off the valve, looking inside it, and then replace the valve, while another would service the cylinder valve before replacing it.

Today, IDEST centres work to set standards. IDEST ensures that test stations and their technicians adhere to CP11:2011 Code of Practice, thus ensuring high-quality service and testing, thereby keeping scuba customers – and the people who fill their cylinders – safe. IDEST centres are tri-annually inspected, and there is an appeals process for customers who feel that their equipment has not been correctly serviced.

IDEST itself is accredited by UKAS to ISO / IEC 17024. (UKAS is the UK’s Accreditation Service and it is recognised by the British Government to assess the competence of organisations that provide certification, testing, inspection and calibration services.) IDEST is therefore also (annually) inspected and checked by the Government to ensure that it also adheres to the highest standards at all times.


Photographs by IDEST, and Rosemary E Lunn/The Underwater Marketing Company

Our gear content is sponsored by Mike’s Dive Store, the UK’s premier dive retailer. For all your diving needs visit them in-store or online for your diving, freediving, snorkelling and servicing.

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