There are four CEN standards for tunneling machinery safety covered by CEN/TC 151 ‘Construction equipment and building material machines – Safety’. These are:
• EN 815:1996+A2:2008 – Safety of unshielded tunnel boring machines and rodless shaft boring machines for rock – Safety requirement
• EN 12110:2002+A1:2008 – Tunnelling machines – Air locks – Safety requirements.
• EN 12111:2002+A1:2009 – Tunnelling machines – Roadheaders, continuous miners and impact rippers – Safety requirements.
• EN 12336:2005+A1:2008 – Tunnelling machines – Shield machines, thrust boring machines, auger boring machines, lining erection equipment – Safety requirements.

All four were updated to reflect the essential safety requirements of the new Machinery Directive, with amendments published at the end of 2009. The further revisioning work undertaken by CEN/TC151/WG4 to address technological changes started on 8 October 2008 at the start of the 36 months required for standard development. Although standards EN 12110 and EN 12111 were revised according to normal procedure, the committee decided that there was now sufficient similarities between unshielded and shielded TBM design that standards EN 815 and EN 12336 should be combined, as well as revised, to form a single standard titled ‘Tunnelling machinery – Safety requirements’.

All the revised standards were intended for CEN enquiry in 2010 and, if they received positive votes by the European members of CEN, will be published in 2012.

Combined tunnelling machinery
It became obvious that, in the light of practical experience, plus the development of dual-mode or hybrid TBMs, that there was no advantage is continuing with two standards for hard-rock and soft-ground machines. Basic design points regarding safety are similar for both. The new standard is also intended to cover future technological developments, and, of the types of machine covered, also includes microtunnelling, reaming and shaft-boring machines. A microtunnelling machine is defined, not by size, but by whether it is remote-controlled allowing man-entry only for maintenance when not operating. All other machines allow man access.

The highest priority in this revision is safe working when accessing the cutterhead for maintenance, since no ‘maintenance-free’ solution is yet available. Where possible, including all cutterheads above 4.5m diameter, cutter replacement must be carried out from behind the cutterhead (e.g., using back loader cutters). Where this is not possible, interlocked doors or guards have to be provided to prevent cutterhead movement from the normal controls. A local control station also has to be established.

Segmental lining erection is also considered in the standard, especially in that the most productive work is still basically manual, despite attempt at automation. The common use of vacuum-assisted erectors has resulted in clear requirements for basic safety factors (SFs), with a minimum SF of 1.5 against pull off or sliding. If devices such as shear pins are not used, the minimum SF shall be 2.5.

The committee says one of the most difficult subjects for agreement in drawing up the new standard was defining minimum requirements for walkways and access openings in a basically confined space working environment. It was agreed that the geometrical limits for access on larger machines should be less restrictive whereas the old standards specified absolute minimum dimensions. The latter have been retained for smaller TBMs, based on the planned diameter inside tunnel support.

The minimum dimensions of walkways effectively determine the minimum dimensions for man access. There must also be consideration of the dimensions for emergency requirements such as stretcher carrying and breathing apparatus by rescue personnel, including maximum distances to ‘safe areas’.

Airlocks – EN 12110
The revision of the safety requirements of this standard had to take into consideration many factors such as human considerations, economics and feasibility. The scope of the standard only covers air locks attached to tunnelling machines and bulkheads for use in tunnels under pressure. More details of these and other hyperbaric equipment will be covered in another feature in T&TI later this year.

The German Federal Ministry of Economics and Labour strongly favoured a revision to address non-conformity with EU directives and to include state-of-the-art requirements. The committee’s drafting group consulted with experts in compressed air work and in requirements for pressure vessels for human occupancy (PVHOs), as well as medical experts.

There is no limit specified in the standard on pressure, hence depth, but it is applicable to 5-bar, or 50m water depth.

It was decided that vibration, noise and electromagnetic compatibility associated with airlocks were non-significant hazards, but the list of significant hazards has been updated.

The design features of pressure vessels and parts has now been harmonised with the European Pressure Equipment Directive 97/23/EC.

For fire protection, fire-fighting and emergency provisions at the equipment control stand are now mandatory. The committee says that requirements for electrical equipment including emergency power supply and lighting are now better structured, with higher levels of light intensity. Also there must be an emergency pressure controller inside the chamber.

Other provisions covered in the revised Standard include:
• More ergonomic chamber dimensions and seating for ‘large operators’ during decompression.
• Larger windows for surveillance.
• Only water heating systems allowed.
• Noise levels (80 db(A)) harmonised with the Machinery Directive.
• Air quality.
• Oxygen breathing system safety.
• Slight changes to provisions for materials and combined air-locks.

Other tunnelling machines – EN 12111
The standard covers roadheaders, continuous miners and impact rippers, the latter consisting of a hydraulic hammer mounted on a crawler chassis. Before this work, the last amendment was to meet the requirements of Directive 2006/42/EC.

Much depends on the application of such machines and the committees CEN/TCs 151 and 196 had agreed this standard only deals with machines used in non-gassy environments. Those needing explosion protection systems are dealt with by CEN/TC196, chiefly, but not exclusively, for mining applications.

The independent CN machinery consultant was highly critical of aspects of the draft amendment to the standard and required a full revision as quickly as possible. The text of the revised standard has now gone to CEN enquiry.

There are said to be no radical changes proposed for the revised standard, but there are a number of detailed changes.

The current standard actually excludes requirements for the hammer used in ‘impact rippers’ and there is no positive inclusion of the crawler carrier either. Therefore ‘impact rippers’ have been removed from the standard and replaced with (detachable) cutterheads and impact hammers as found on versatile carriers such as hydraulic excavators. Roadheaders and continuous miners remain covered.

The tandard now requires the machine manufacturer to provide a main switch box, for electric drive machines, on the trailing cable between the machine and the tunnel supply. The location defines division of responsibility between the supplier of electrical power and the machine manufacturer.

There are also more rigorous requirements for access to parts of the machine to allow safe operation and maintenance. As regards the latter, it is now a design principle that maintenance should be able to be carried out at ground level.

Dust is well known as a possible hazard with such open cutting machines, especially silica inhalation. Requirements have been established for machines and attachments to reduce dust production and to improve dust suppression. Other revised provisions of the standard include:
• Better lighting of machine and surrounds.
• With heavier machines of low centre-of-gravity, stability is no longer an issue.
• Remote operation, automatic profiling and guidance provisions included according to the state of the art.
• Fixed fire extinguishers.
• Fuel and other fluid storage harmonized with other crawler machinery (in construction).
• Provision for towing, lifting and transport included according to Directive 2006/4/EC.

Next stages
The revised standards are now under CEN enquiry, due to be completed this spring. There may still be suggestions for changes or modifications at this stage before final publication, but the Working Group states that the basic content should remain.

Member countries then vote on the drafts (usually abstaining if not interested in the topic) and submit comments to CEN.

In parallel the independent CEN machinery consultant assesses the draft and makes comments. All comments are then resolved by the CEN Working Group and the document goes for formal vote. If positive it is translated into the official languages and becomes a harmonized standard after publication in the Official Journal of the European Union. If all goes well, revisions will be published in 2012.

The Working Group feels the target to include and reflect the latest development in what is still a fast developing technology for mechanised tunnelling (including the use of compressed air) has been achieved. Wherever possible, foreseeable future development has been considered as well. As has already been the case with the present CEN tunnelling standards, the Working Group feels that the revised version may very well be considered as a guideline far outside the CEN area.

Non-circular TBM air-lock with 1.5m headroom for a ‘large operator’