Britain’s standard for safety in tunnelling was first published in 1982. Notably, ‘health’ was omitted from its title (and the rest of the document) and the whole thing reflected how tunnelling was undertaken at the time; the 56-page document had a great deal to say about hand mining techniques and practice, as well as timbering, with far less ink devoted to the working environment and plant/equipment.
Further revisions to the document were published in 1991, 2001 and 2011, with occupational health first appearing in the 2001 edition. The 2011 edition saw the title updated to reflect the changing focus of the industry.
The basic structure of the document has not changed in its entire history – there are still 26 clauses – but the content has changed drastically, with BS6164:2019 weighing in at 217 pages compared to the original 56.
Mechanised tunnelling and more emphasis of occupational health hazards as well as plant and equipment are the biggest reasons for the increased page count.
The New Revision
Tunnelling technology is constantly evolving and with it the health and safety issues evolve also. Greater mechanisation, remote control and automation bring benefits in removing miners from the most hazardous aspects of tunnelling, however they also bring problems in terms of machinery control and safety. The increase in SCL work has brought greater exposure to dust and diesel particulates, and health has generally become a much more important topic.
The numerous changes in the revised standard have arisen due to a number of reasons. Some are simply rationalisations, while others have come from legislative changes in Europe, some from lessons learnt since the 2011 revision was published, and some from changes to tunnelling practice or advances in technology over the last decade, which allows for improvements to health and safety practice (and sometimes the creation of new hazards).
BS 6164:2019 addresses some major concerns. For example, the guidance on dust now makes it clear that extraction ventilation is the preferred technique for containing emissions. In addition, the control regime has been changed from an 8-hour average exposure to real time monitoring with control based on 15-minute short term limits. This recognises the large variation in dust levels which can occur over a working shift in tunnelling.
The use of lithium batteries has grown extensively over the past decade. Whilst battery power may be low emission in terms of a oxides of carbon and nitrogen, the batteries contain chemicals which are highly toxic if released in a fire. In addition, any fire will be difficult to extinguish without the use of specialist extinguishants.
Some key changes are:
- Legislative changes since 2011 include the classification of respirable crystalline silica as a human carcinogen, prompting more rigorous guidance on reducing emissions at source and dust control primarily through extraction ventilation. Another regulatory change that is likely to come in, during the lifetime of the standard, is a further reduction in exposure levels to oxides of nitrogen
- Under the title of “safety of permanent and temporary works” Clause 6.4 of the standard provides extensive guidance on how the design checking process for tunnel linings should be undertaken. It emphasises the need to provide equally robust checking of the primary lining whether it is permanent or temporary in nature. It requires the involvement of the client in the design check process and provides a framework for the resolution of disputes between designer and checker. It requires the check category to be proportional to the risk from failure and for the checker to certify three things – the design meets the design brief, is constructible and is safe. Guidance is given on the competence of the checker and on contractors acting as checkers.
- Clause 7 has been extensively rewritten, but with few technical changes, to reflect the revised clause title ‘Excavation and control of ground movement’. Soft ground and hard rock tunnelling is covered, as well as pipe and box jacking.
- The guidance on ground improvement techniques, including freezing and grouting, has been moved to Clause 9.
- The guidance on plant and equipment safety along with materials handling has been rationalized, and a general edit of this clause has been undertaken.
- Guidance on all methods of materials handling has been brought together in Clause 23
- Guidance on plant and equipment safety, including hired plant, is set out in Clause 24. The requirements for vehicle fire suppression and for the use of surface construction plant underground have been comprehensively addressed.
- A major change in tunnelling technology just starting to appear in UK tunnelling is the use of high pressure compressed air techniques for cutterhead interventions. Guidance on the technique is now included in the standard.
- Shafts are an often forgotten but vitally important aspect of tunnelling. The past decade has seen significant increases in shaft size and depth along with changes in construction methods. As a consequence, Clause 20 on shafts has been considerably extended to address these changes. A formal definition of when a shaft should be considered a confined space has been included.
- The basic use of electricity on tunnel sites has not changed. However, with ever larger tunnel boring machines being used, the power demand on-site has grown considerably. Consequently, clause 25 on electrical safety has been extensively revised to reflect current electrical power engineering practice.
Using the Standard
It is recommended that anyone plying their trade in the UK should read through BS6164 carefully for changes that might be relevant to them, as every clause has changed in some way. As with almost all BSI standards, BS 6164 is guidance rather than law. However, HSE was represented on the drafting committee and contributed to the text. BS 6164:2019 therefore takes account of HSE’s policy on tunnelling safety. Experience has shown that the courts place considerable emphasis on BSI documents because of the way they represent consensus between all sides of industry and the regulator on good practice.
BS 6164 depends heavily on a number of other document such as BS EN 16191:2014, Tunnelling machinery — Safety requirements; BS EN 12110:2014, Tunnelling machines — Air locks — Safety requirements; and the British Tunnelling Society Compressed Air Working Group’s ‘Guide to the work in compressed air regulations’. These are all currently being extensively revised. BS 6164 also refers to the International Tunnelling Association/ British Tunnelling Society Compressed Air Working Group Report 10, ‘Guidelines for good working practice in high pressure compressed air’.
BS 6164:2019 also acts as the default standard for other industry publications such as the Joint Code of Practice for Risk Management of Tunnel Works and the International Tunnel Insurance Group code.
The next review will be in 2024 and will almost certainly result in a further revision of the standard. With BS6164 there has been a comprehensive and thorough revision in each instance.
Indeed, the fact that the committee members do this on a voluntary basis and can only devote a limited amount of time to it means that the revision takes 3-5 years each time, and some information in the actual standard could be more up-to-date than it inevitably is.
As for what that edition might involve, Lamont concludes that a prediction he will make is that having been on the BS 6164 drafting committee since 1987, and having chaired three revisions of the standard to date, he will not be chairing a fourth.
