BS 8478 – Breathing Gases for Diving and Hyperbaric Applications

This standard is virtually impossible to achieve using air produced by standard breathing air compressors and the low levels of contaminants required cannot be effectively measured by conventional methods; it makes a laboratory test the only reliable method.

The HSE is well aware of the practical problems that this standards poses for recreational diving operations. A European version of this Standard is being developed. No doubt, when the EN standard is published, further HSE guidance will follow. In the meantime, ASSET Members are advised to ensure that they are producing air, particularly for the production of Nitrox or Tri-mix, to the highest practicable standard.

Meeting the low oil level required will be the greatest challenge. Adding a high volume, low velocity secondary filter  (as recommended in the ASSET Nitrox Manual) that provides maximum "Dwell" of the air being filtered will go some way to achieving this. We also recommend that filters are replaced in good time and that any air purity test is carried out at the end of the filter's life not when it is new. This will ensure a "worst case" measurement.

Additionally, we recommend that, in addition to any quarterly "in house" testing that may be carried out, a laboratory test is carried out at least 6 monthly intervals. A relatively economical and practicable laboratory test is available from Aquatron in Glasgow. http:/www.airpurity.com/how_apa.htm

Please also read the following HSE guidance:

BS 8478 – Breathing Gases for Diving and Hyperbaric

British Standard 8478 specifies requirements for the composition and purity of breathing gases, other than compressed air, for diving and hyperbaric applications. It specifies reduced levels of contaminants compared with those required to meet the compressed air standard, BS EN 12021. HSE supports British Standards as a means to enhance safety and provide guidance to industry. In particular HSE endorses the need for increased gas purity, over and above the levels required in BS EN 12021, where equipment is exposed to oxygen levels greater than 21% and for gas mixes used at increased depths. Compliance with a British Standard is, however not a legal requirement but their observance provides a means of demonstrating that appropriate risk controls have been applied.  It is open to gas manufacturers/providers to produce gas to their own standard provided these also apply appropriate risk controls. Ultimately it will be up to the courts to decide if such other standards are sufficient.

HSE is aware that areas of the recreational diving industry have concerns with some aspects of BS 8478.  It is believed these concerns are based on whether the demanding purity criteria are justified for all gas mixes used in recreational diving, as well as the potential impact the standard could have on the continued use of Nitrox in the recreational sector.

BS 8478 is currently being considered as a basis for a new European standard. When this European standard is finalised it will supersede BS 8478 which will then be withdrawn. The process for developing the new standard is now underway within Europe and the resulting standard will almost certainly be different in some respects from the current BS 8478.

In the interim period before the European standard is finalised and published HSE expects the recreational diving industry to take all reasonably practicable steps to minimise the contaminants in the gases other than air which they provide, and where practicable to meet the contaminant criteria detailed in BS 8478. These steps should include robust systems of work to ensure that any impurities are maintained at the lowest levels practicable as well as periodic tests to ensure the contaminants are maintained at these low levels. BS 8478 currently requires testing at least every 6 months.

In the event of diving incidents where gases other than air have been used, the breathing gas composition and purity criteria in BS 8478 will continue to be referred to as part of the investigation process. Should these investigations lead to legal proceedings, and the gas provider did not follow the requirements in BS 8478, it will be up to a court to decide if the steps taken to ensure the purity of the breathing gas were sufficient.

Recreational diving gas providers may wish to take account of the views of their insurers when deciding their course of action.  

The process for developing the new European standard is now underway. Stakeholders within recreational diving are urged to actively participate in this process to ensure the new European standard both enhance safety and is workable for all sectors of the diving industry.

Cylinder Labelling 

Identification of Contents

Cylinder identification should always follow local standards, in Europe (including the UK) EN ISO 7225;2007 replaced BS EN 1089-2 as the standard for cylinder labelling. This is an international standard so all cylinders anywhere in the world should be labelled accordingly (unless there is a different local requirement)
These “precautionary labels” must contain an international hazard diamond together with the name and UN number of the gas or gas mixture. If this name is not a real name, e.g. Nitrox, then the chemical formula must be included e.g. N2/O2. If the mixture can vary, as with Nitrox, Heliox and Trimix, then the percentages of the mixture must be included on this or on a separate label. The label must also contain the filling company’s name and contact details. Additionally, in the UK, the HSE have asked the industry to include the Maximum Operating Depth

EN 1089-3 defines the colours that identify either the hazard or the specific gas. A combination of colours is used to identify a compound hazard or a gas mixture. In this Standard, only the shoulder colour is significant, therefore, the cylinder body colour could be used for visibility or personal identification. The shoulder colours of an Air or Nitrox cylinder should be Black and White; Heliox should be White and Brown and Trimix should be Black, White and Brown.

Note: The primary purpose of cylinder marking is to inform those attending accidents/emergencies what the cylinder contains.